[SCSI] iscsi: convert xmit path to iscsi chunks

Convert xmit to iscsi chunks.

from michaelc@cs.wisc.edu:

Bug fixes, more digest integration, sg chaining conversion and other
sg wrapper changes, coding style sync up, and removal of io fields,
like pdu_sent, that are not needed.

Signed-off-by: Olaf Kirch <olaf.kirch@oracle.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 526 insertions, 807 deletions

diff --git a/drivers/scsi/iscsi_tcp.c b/drivers/scsi/iscsi_tcp.c
index 9b418522c9bf..7212fe95a66d 100644
--- a/drivers/scsi/iscsi_tcp.c
+++ b/drivers/scsi/iscsi_tcp.c
@@ -68,56 +68,10 @@ static unsigned int iscsi_max_lun = 512;
 module_param_named(max_lun, iscsi_max_lun, uint, S_IRUGO);
 
 static int iscsi_tcp_hdr_recv_done(struct iscsi_tcp_conn *tcp_conn,
-                                   struct iscsi_chunk *chunk);
-
-static inline void
-iscsi_buf_init_iov(struct iscsi_buf *ibuf, char *vbuf, int size)
-{
-        ibuf->sg.page = virt_to_page(vbuf);
-        ibuf->sg.offset = offset_in_page(vbuf);
-        ibuf->sg.length = size;
-        ibuf->sent = 0;
-        ibuf->use_sendmsg = 1;
-}
-
-static inline void
-iscsi_buf_init_sg(struct iscsi_buf *ibuf, struct scatterlist *sg)
-{
-        ibuf->sg.page = sg->page;
-        ibuf->sg.offset = sg->offset;
-        ibuf->sg.length = sg->length;
-        /*
-         * Fastpath: sg element fits into single page
-         */
-        if (sg->length + sg->offset <= PAGE_SIZE && !PageSlab(sg->page))
-                ibuf->use_sendmsg = 0;
-        else
-                ibuf->use_sendmsg = 1;
-        ibuf->sent = 0;
-}
-
-static inline int
-iscsi_buf_left(struct iscsi_buf *ibuf)
-{
-        int rc;
-
-        rc = ibuf->sg.length - ibuf->sent;
-        BUG_ON(rc < 0);
-        return rc;
-}
-
-static inline void
-iscsi_hdr_digest(struct iscsi_conn *conn, struct iscsi_buf *buf,
-                 u8* crc)
-{
-        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
-
-        crypto_hash_digest(&tcp_conn->tx_hash, &buf->sg, buf->sg.length, crc);
-        buf->sg.length += ISCSI_DIGEST_SIZE;
-}
+                                   struct iscsi_segment *segment);
 
 /*
- * Scatterlist handling: inside the iscsi_chunk, we
+ * Scatterlist handling: inside the iscsi_segment, we
  * remember an index into the scatterlist, and set data/size
  * to the current scatterlist entry. For highmem pages, we
  * kmap as needed.
@@ -130,60 +84,72 @@ iscsi_hdr_digest(struct iscsi_conn *conn, struct iscsi_buf *buf,
  */
 
 /**
- * iscsi_tcp_chunk_init_sg - init indicated scatterlist entry
- * @chunk: the buffer object
- * @idx: index into scatterlist
+ * iscsi_tcp_segment_init_sg - init indicated scatterlist entry
+ * @segment: the buffer object
+ * @sg: scatterlist
  * @offset: byte offset into that sg entry
  *
- * This function sets up the chunk so that subsequent
+ * This function sets up the segment so that subsequent
  * data is copied to the indicated sg entry, at the given
  * offset.
  */
 static inline void
-iscsi_tcp_chunk_init_sg(struct iscsi_chunk *chunk,
-                        unsigned int idx, unsigned int offset)
+iscsi_tcp_segment_init_sg(struct iscsi_segment *segment,
+                          struct scatterlist *sg, unsigned int offset)
 {
-        struct scatterlist *sg;
-
-        BUG_ON(chunk->sg == NULL);
-
-        sg = &chunk->sg[idx];
-        chunk->sg_index = idx;
-        chunk->sg_offset = offset;
-        chunk->size = min(sg->length - offset, chunk->total_size);
-        chunk->data = NULL;
+        segment->sg = sg;
+        segment->sg_offset = offset;
+        segment->size = min(sg->length - offset,
+                            segment->total_size - segment->total_copied);
+        segment->data = NULL;
 }
 
 /**
- * iscsi_tcp_chunk_map - map the current S/G page
- * @chunk: iscsi chunk
+ * iscsi_tcp_segment_map - map the current S/G page
+ * @segment: iscsi_segment
+ * @recv: 1 if called from recv path
  *
  * We only need to possibly kmap data if scatter lists are being used,
  * because the iscsi passthrough and internal IO paths will never use high
  * mem pages.
  */
 static inline void
-iscsi_tcp_chunk_map(struct iscsi_chunk *chunk)
+iscsi_tcp_segment_map(struct iscsi_segment *segment, int recv)
 {
         struct scatterlist *sg;
 
-        if (chunk->data != NULL || !chunk->sg)
+        if (segment->data != NULL || !segment->sg)
                 return;
 
-        sg = &chunk->sg[chunk->sg_index];
-        BUG_ON(chunk->sg_mapped);
+        sg = segment->sg;
+        BUG_ON(segment->sg_mapped);
         BUG_ON(sg->length == 0);
-        chunk->sg_mapped = kmap_atomic(sg->page, KM_SOFTIRQ0);
-        chunk->data = chunk->sg_mapped + sg->offset + chunk->sg_offset;
+
+        /*
+         * If the page count is greater than one it is ok to send
+         * to the network layer's zero copy send path. If not we
+         * have to go the slow sendmsg path. We always map for the
+         * recv path.
+         */
+        if (page_count(sg_page(sg)) >= 1 && !recv)
+                return;
+
+        debug_tcp("iscsi_tcp_segment_map %s %p\n", recv ? "recv" : "xmit",
+                  segment);
+        segment->sg_mapped = kmap_atomic(sg_page(sg), KM_SOFTIRQ0);
+        segment->data = segment->sg_mapped + sg->offset + segment->sg_offset;
 }
 
 static inline void
-iscsi_tcp_chunk_unmap(struct iscsi_chunk *chunk)
+iscsi_tcp_segment_unmap(struct iscsi_segment *segment)
 {
-        if (chunk->sg_mapped) {
-                kunmap_atomic(chunk->sg_mapped, KM_SOFTIRQ0);
-                chunk->sg_mapped = NULL;
-                chunk->data = NULL;
+        debug_tcp("iscsi_tcp_segment_unmap %p\n", segment);
+
+        if (segment->sg_mapped) {
+                debug_tcp("iscsi_tcp_segment_unmap valid\n");
+                kunmap_atomic(segment->sg_mapped, KM_SOFTIRQ0);
+                segment->sg_mapped = NULL;
+                segment->data = NULL;
         }
 }
 
@@ -191,23 +157,24 @@ iscsi_tcp_chunk_unmap(struct iscsi_chunk *chunk)
  * Splice the digest buffer into the buffer
  */
 static inline void
-iscsi_tcp_chunk_splice_digest(struct iscsi_chunk *chunk, void *digest)
+iscsi_tcp_segment_splice_digest(struct iscsi_segment *segment, void *digest)
 {
-        chunk->data = digest;
-        chunk->digest_len = ISCSI_DIGEST_SIZE;
-        chunk->total_size += ISCSI_DIGEST_SIZE;
-        chunk->size = ISCSI_DIGEST_SIZE;
-        chunk->copied = 0;
-        chunk->sg = NULL;
-        chunk->sg_index = 0;
-        chunk->hash = NULL;
+        segment->data = digest;
+        segment->digest_len = ISCSI_DIGEST_SIZE;
+        segment->total_size += ISCSI_DIGEST_SIZE;
+        segment->size = ISCSI_DIGEST_SIZE;
+        segment->copied = 0;
+        segment->sg = NULL;
+        segment->hash = NULL;
 }
 
 /**
- * iscsi_tcp_chunk_done - check whether the chunk is complete
- * @chunk: iscsi chunk to check
+ * iscsi_tcp_segment_done - check whether the segment is complete
+ * @segment: iscsi segment to check
+ * @recv: set to one of this is called from the recv path
+ * @copied: number of bytes copied
  *
- * Check if we're done receiving this chunk. If the receive
+ * Check if we're done receiving this segment. If the receive
  * buffer is full but we expect more data, move on to the
  * next entry in the scatterlist.
  *
@@ -217,62 +184,145 @@ iscsi_tcp_chunk_splice_digest(struct iscsi_chunk *chunk, void *digest)
  * This function must be re-entrant.
  */
 static inline int
-iscsi_tcp_chunk_done(struct iscsi_chunk *chunk)
+iscsi_tcp_segment_done(struct iscsi_segment *segment, int recv, unsigned copied)
 {
         static unsigned char padbuf[ISCSI_PAD_LEN];
+        struct scatterlist sg;
         unsigned int pad;
 
-        if (chunk->copied < chunk->size) {
-                iscsi_tcp_chunk_map(chunk);
+        debug_tcp("copied %u %u size %u %s\n", segment->copied, copied,
+                  segment->size, recv ? "recv" : "xmit");
+        if (segment->hash && copied) {
+                /*
+                 * If a segment is kmapd we must unmap it before sending
+                 * to the crypto layer since that will try to kmap it again.
+                 */
+                iscsi_tcp_segment_unmap(segment);
+
+                if (!segment->data) {
+                        sg_init_table(&sg, 1);
+                        sg_set_page(&sg, sg_page(segment->sg), copied,
+                                    segment->copied + segment->sg_offset +
+                                                        segment->sg->offset);
+                } else
+                        sg_init_one(&sg, segment->data + segment->copied,
+                                    copied);
+                crypto_hash_update(segment->hash, &sg, copied);
+        }
+
+        segment->copied += copied;
+        if (segment->copied < segment->size) {
+                iscsi_tcp_segment_map(segment, recv);
                 return 0;
         }
 
-        chunk->total_copied += chunk->copied;
-        chunk->copied = 0;
-        chunk->size = 0;
+        segment->total_copied += segment->copied;
+        segment->copied = 0;
+        segment->size = 0;
 
         /* Unmap the current scatterlist page, if there is one. */
-        iscsi_tcp_chunk_unmap(chunk);
+        iscsi_tcp_segment_unmap(segment);
 
         /* Do we have more scatterlist entries? */
-        if (chunk->total_copied < chunk->total_size) {
+        debug_tcp("total copied %u total size %u\n", segment->total_copied,
+                   segment->total_size);
+        if (segment->total_copied < segment->total_size) {
                 /* Proceed to the next entry in the scatterlist. */
-                iscsi_tcp_chunk_init_sg(chunk, chunk->sg_index + 1, 0);
-                iscsi_tcp_chunk_map(chunk);
-                BUG_ON(chunk->size == 0);
+                iscsi_tcp_segment_init_sg(segment, sg_next(segment->sg),
+                                          0);
+                iscsi_tcp_segment_map(segment, recv);
+                BUG_ON(segment->size == 0);
                 return 0;
         }
 
         /* Do we need to handle padding? */
-        pad = iscsi_padding(chunk->total_copied);
+        pad = iscsi_padding(segment->total_copied);
         if (pad != 0) {
                 debug_tcp("consume %d pad bytes\n", pad);
-                chunk->total_size += pad;
-                chunk->size = pad;
-                chunk->data = padbuf;
+                segment->total_size += pad;
+                segment->size = pad;
+                segment->data = padbuf;
                 return 0;
         }
 
         /*
-         * Set us up for receiving the data digest. hdr digest
+         * Set us up for transferring the data digest. hdr digest
          * is completely handled in hdr done function.
          */
-        if (chunk->hash) {
-                if (chunk->digest_len == 0) {
-                        crypto_hash_final(chunk->hash, chunk->digest);
-                        iscsi_tcp_chunk_splice_digest(chunk,
-                                                      chunk->recv_digest);
-                        return 0;
-                }
+        if (segment->hash) {
+                crypto_hash_final(segment->hash, segment->digest);
+                iscsi_tcp_segment_splice_digest(segment,
+                                 recv ? segment->recv_digest : segment->digest);
+                return 0;
         }
 
         return 1;
 }
 
 /**
- * iscsi_tcp_chunk_recv - copy data to chunk
+ * iscsi_tcp_xmit_segment - transmit segment
  * @tcp_conn: the iSCSI TCP connection
- * @chunk: the buffer to copy to
+ * @segment: the buffer to transmnit
+ *
+ * This function transmits as much of the buffer as
+ * the network layer will accept, and returns the number of
+ * bytes transmitted.
+ *
+ * If CRC hashing is enabled, the function will compute the
+ * hash as it goes. When the entire segment has been transmitted,
+ * it will retrieve the hash value and send it as well.
+ */
+static int
+iscsi_tcp_xmit_segment(struct iscsi_tcp_conn *tcp_conn,
+                       struct iscsi_segment *segment)
+{
+        struct socket *sk = tcp_conn->sock;
+        unsigned int copied = 0;
+        int r = 0;
+
+        while (!iscsi_tcp_segment_done(segment, 0, r)) {
+                struct scatterlist *sg;
+                unsigned int offset, copy;
+                int flags = 0;
+
+                r = 0;
+                offset = segment->copied;
+                copy = segment->size - offset;
+
+                if (segment->total_copied + segment->size < segment->total_size)
+                        flags |= MSG_MORE;
+
+                /* Use sendpage if we can; else fall back to sendmsg */
+                if (!segment->data) {
+                        sg = segment->sg;
+                        offset += segment->sg_offset + sg->offset;
+                        r = tcp_conn->sendpage(sk, sg_page(sg), offset, copy,
+                                               flags);
+                } else {
+                        struct msghdr msg = { .msg_flags = flags };
+                        struct kvec iov = {
+                                .iov_base = segment->data + offset,
+                                .iov_len = copy
+                        };
+
+                        r = kernel_sendmsg(sk, &msg, &iov, 1, copy);
+                }
+
+                if (r < 0) {
+                        iscsi_tcp_segment_unmap(segment);
+                        if (copied || r == -EAGAIN)
+                                break;
+                        return r;
+                }
+                copied += r;
+        }
+        return copied;
+}
+
+/**
+ * iscsi_tcp_segment_recv - copy data to segment
+ * @tcp_conn: the iSCSI TCP connection
+ * @segment: the buffer to copy to
  * @ptr: data pointer
  * @len: amount of data available
  *
@@ -287,29 +337,24 @@ iscsi_tcp_chunk_done(struct iscsi_chunk *chunk)
  * just way we do for network layer checksums.
  */
 static int
-iscsi_tcp_chunk_recv(struct iscsi_tcp_conn *tcp_conn,
-                     struct iscsi_chunk *chunk, const void *ptr,
-                     unsigned int len)
+iscsi_tcp_segment_recv(struct iscsi_tcp_conn *tcp_conn,
+                       struct iscsi_segment *segment, const void *ptr,
+                       unsigned int len)
 {
-        struct scatterlist sg;
-        unsigned int copy, copied = 0;
-
-        while (!iscsi_tcp_chunk_done(chunk)) {
-                if (copied == len)
-                        goto out;
+        unsigned int copy = 0, copied = 0;
 
-                copy = min(len - copied, chunk->size - chunk->copied);
-                memcpy(chunk->data + chunk->copied, ptr + copied, copy);
-
-                if (chunk->hash) {
-                        sg_init_one(&sg, ptr + copied, copy);
-                        crypto_hash_update(chunk->hash, &sg, copy);
+        while (!iscsi_tcp_segment_done(segment, 1, copy)) {
+                if (copied == len) {
+                        debug_tcp("iscsi_tcp_segment_recv copied %d bytes\n",
+                                  len);
+                        break;
                 }
-                chunk->copied += copy;
+
+                copy = min(len - copied, segment->size - segment->copied);
+                debug_tcp("iscsi_tcp_segment_recv copying %d\n", copy);
+                memcpy(segment->data + segment->copied, ptr + copied, copy);
                 copied += copy;
         }
-
-out:
         return copied;
 }
 
@@ -325,12 +370,13 @@ iscsi_tcp_dgst_header(struct hash_desc *hash, const void *hdr, size_t hdrlen,
 
 static inline int
 iscsi_tcp_dgst_verify(struct iscsi_tcp_conn *tcp_conn,
-                      struct iscsi_chunk *chunk)
+                      struct iscsi_segment *segment)
 {
-        if (!chunk->digest_len)
+        if (!segment->digest_len)
                 return 1;
 
-        if (memcmp(chunk->recv_digest, chunk->digest, chunk->digest_len)) {
+        if (memcmp(segment->recv_digest, segment->digest,
+                   segment->digest_len)) {
                 debug_scsi("digest mismatch\n");
                 return 0;
         }
@@ -339,55 +385,59 @@ iscsi_tcp_dgst_verify(struct iscsi_tcp_conn *tcp_conn,
 }
 
 /*
- * Helper function to set up chunk buffer
+ * Helper function to set up segment buffer
  */
 static inline void
-__iscsi_chunk_init(struct iscsi_chunk *chunk, size_t size,
-                   iscsi_chunk_done_fn_t *done, struct hash_desc *hash)
+__iscsi_segment_init(struct iscsi_segment *segment, size_t size,
+                     iscsi_segment_done_fn_t *done, struct hash_desc *hash)
 {
-        memset(chunk, 0, sizeof(*chunk));
-        chunk->total_size = size;
-        chunk->done = done;
+        memset(segment, 0, sizeof(*segment));
+        segment->total_size = size;
+        segment->done = done;
 
         if (hash) {
-                chunk->hash = hash;
+                segment->hash = hash;
                 crypto_hash_init(hash);
         }
 }
 
 static inline void
-iscsi_chunk_init_linear(struct iscsi_chunk *chunk, void *data, size_t size,
-                        iscsi_chunk_done_fn_t *done, struct hash_desc *hash)
+iscsi_segment_init_linear(struct iscsi_segment *segment, void *data,
+                          size_t size, iscsi_segment_done_fn_t *done,
+                          struct hash_desc *hash)
 {
-        __iscsi_chunk_init(chunk, size, done, hash);
-        chunk->data = data;
-        chunk->size = size;
+        __iscsi_segment_init(segment, size, done, hash);
+        segment->data = data;
+        segment->size = size;
 }
 
 static inline int
-iscsi_chunk_seek_sg(struct iscsi_chunk *chunk,
-                    struct scatterlist *sg, unsigned int sg_count,
-                    unsigned int offset, size_t size,
-                    iscsi_chunk_done_fn_t *done, struct hash_desc *hash)
+iscsi_segment_seek_sg(struct iscsi_segment *segment,
+                      struct scatterlist *sg_list, unsigned int sg_count,
+                      unsigned int offset, size_t size,
+                      iscsi_segment_done_fn_t *done, struct hash_desc *hash)
 {
+        struct scatterlist *sg;
         unsigned int i;
 
-        __iscsi_chunk_init(chunk, size, done, hash);
-        for (i = 0; i < sg_count; ++i) {
-                if (offset < sg[i].length) {
-                        chunk->sg = sg;
-                        chunk->sg_count = sg_count;
-                        iscsi_tcp_chunk_init_sg(chunk, i, offset);
+        debug_scsi("iscsi_segment_seek_sg offset %u size %llu\n",
+                  offset, size);
+        __iscsi_segment_init(segment, size, done, hash);
+        for_each_sg(sg_list, sg, sg_count, i) {
+                debug_scsi("sg %d, len %u offset %u\n", i, sg->length,
+                           sg->offset);
+                if (offset < sg->length) {
+                        iscsi_tcp_segment_init_sg(segment, sg, offset);
                         return 0;
                 }
-                offset -= sg[i].length;
+                offset -= sg->length;
         }
 
         return ISCSI_ERR_DATA_OFFSET;
 }
 
 /**
- * iscsi_tcp_hdr_recv_prep - prep chunk for hdr reception
+ * iscsi_tcp_hdr_recv_prep - prep segment for hdr reception
  * @tcp_conn: iscsi connection to prep for
  *
  * This function always passes NULL for the hash argument, because when this
@@ -399,7 +449,7 @@ iscsi_tcp_hdr_recv_prep(struct iscsi_tcp_conn *tcp_conn)
 {
         debug_tcp("iscsi_tcp_hdr_recv_prep(%p%s)\n", tcp_conn,
                   tcp_conn->iscsi_conn->hdrdgst_en ? ", digest enabled" : "");
-        iscsi_chunk_init_linear(&tcp_conn->in.chunk,
+        iscsi_segment_init_linear(&tcp_conn->in.segment,
                                 tcp_conn->in.hdr_buf, sizeof(struct iscsi_hdr),
                                 iscsi_tcp_hdr_recv_done, NULL);
 }
@@ -409,12 +459,12 @@ iscsi_tcp_hdr_recv_prep(struct iscsi_tcp_conn *tcp_conn)
  */
 static int
 iscsi_tcp_data_recv_done(struct iscsi_tcp_conn *tcp_conn,
-                         struct iscsi_chunk *chunk)
+                         struct iscsi_segment *segment)
 {
         struct iscsi_conn *conn = tcp_conn->iscsi_conn;
         int rc = 0;
 
-        if (!iscsi_tcp_dgst_verify(tcp_conn, chunk))
+        if (!iscsi_tcp_dgst_verify(tcp_conn, segment))
                 return ISCSI_ERR_DATA_DGST;
 
         rc = iscsi_complete_pdu(conn, tcp_conn->in.hdr,
@@ -435,7 +485,7 @@ iscsi_tcp_data_recv_prep(struct iscsi_tcp_conn *tcp_conn)
         if (conn->datadgst_en)
                 rx_hash = &tcp_conn->rx_hash;
 
-        iscsi_chunk_init_linear(&tcp_conn->in.chunk,
+        iscsi_segment_init_linear(&tcp_conn->in.segment,
                                 conn->data, tcp_conn->in.datalen,
                                 iscsi_tcp_data_recv_done, rx_hash);
 }
@@ -448,7 +498,6 @@ iscsi_tcp_cleanup_ctask(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
 {
         struct iscsi_tcp_cmd_task *tcp_ctask = ctask->dd_data;
         struct iscsi_r2t_info *r2t;
-        struct scsi_cmnd *sc;
 
         /* flush ctask's r2t queues */
         while (__kfifo_get(tcp_ctask->r2tqueue, (void*)&r2t, sizeof(void*))) {
@@ -457,12 +506,12 @@ iscsi_tcp_cleanup_ctask(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
                 debug_scsi("iscsi_tcp_cleanup_ctask pending r2t dropped\n");
         }
 
-        sc = ctask->sc;
-        if (unlikely(!sc))
-                return;
-
-        tcp_ctask->xmstate = XMSTATE_IDLE;
-        tcp_ctask->r2t = NULL;
+        r2t = tcp_ctask->r2t;
+        if (r2t != NULL) {
+                __kfifo_put(tcp_ctask->r2tpool.queue, (void*)&r2t,
+                            sizeof(void*));
+                tcp_ctask->r2t = NULL;
+        }
 }
 
 /**
@@ -481,11 +530,6 @@ iscsi_data_rsp(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
         int datasn = be32_to_cpu(rhdr->datasn);
 
         iscsi_update_cmdsn(session, (struct iscsi_nopin*)rhdr);
-        /*
-         * setup Data-In byte counter (gets decremented..)
-         */
-        ctask->data_count = tcp_conn->in.datalen;
-
         if (tcp_conn->in.datalen == 0)
                 return 0;
 
@@ -543,9 +587,6 @@ iscsi_solicit_data_init(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask,
                         struct iscsi_r2t_info *r2t)
 {
         struct iscsi_data *hdr;
-        struct scsi_cmnd *sc = ctask->sc;
-        int i, sg_count = 0;
-        struct scatterlist *sg;
 
         hdr = &r2t->dtask.hdr;
         memset(hdr, 0, sizeof(struct iscsi_data));
@@ -569,34 +610,6 @@ iscsi_solicit_data_init(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask,
         conn->dataout_pdus_cnt++;
 
         r2t->sent = 0;
-
-        iscsi_buf_init_iov(&r2t->headbuf, (char*)hdr,
-                           sizeof(struct iscsi_hdr));
-
-        sg = scsi_sglist(sc);
-        r2t->sg = NULL;
-        for (i = 0; i < scsi_sg_count(sc); i++, sg += 1) {
-                /* FIXME: prefetch ? */
-                if (sg_count + sg->length > r2t->data_offset) {
-                        int page_offset;
-
-                        /* sg page found! */
-
-                        /* offset within this page */
-                        page_offset = r2t->data_offset - sg_count;
-
-                        /* fill in this buffer */
-                        iscsi_buf_init_sg(&r2t->sendbuf, sg);
-                        r2t->sendbuf.sg.offset += page_offset;
-                        r2t->sendbuf.sg.length -= page_offset;
-
-                        /* xmit logic will continue with next one */
-                        r2t->sg = sg + 1;
-                        break;
-                }
-                sg_count += sg->length;
-        }
-        BUG_ON(r2t->sg == NULL);
 }
 
 /**
@@ -670,7 +683,6 @@ iscsi_r2t_rsp(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
 
         tcp_ctask->exp_datasn = r2tsn + 1;
         __kfifo_put(tcp_ctask->r2tqueue, (void*)&r2t, sizeof(void*));
-        tcp_ctask->xmstate |= XMSTATE_SOL_HDR_INIT;
         conn->r2t_pdus_cnt++;
 
         iscsi_requeue_ctask(ctask);
@@ -684,13 +696,13 @@ iscsi_r2t_rsp(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
  */
 static int
 iscsi_tcp_process_data_in(struct iscsi_tcp_conn *tcp_conn,
-                          struct iscsi_chunk *chunk)
+                          struct iscsi_segment *segment)
 {
         struct iscsi_conn *conn = tcp_conn->iscsi_conn;
         struct iscsi_hdr *hdr = tcp_conn->in.hdr;
         int rc;
 
-        if (!iscsi_tcp_dgst_verify(tcp_conn, chunk))
+        if (!iscsi_tcp_dgst_verify(tcp_conn, segment))
                 return ISCSI_ERR_DATA_DGST;
 
         /* check for non-exceptional status */
@@ -762,7 +774,7 @@ iscsi_tcp_hdr_dissect(struct iscsi_conn *conn, struct iscsi_hdr *hdr)
                         /*
                          * Setup copy of Data-In into the Scsi_Cmnd
                          * Scatterlist case:
-                         * We set up the iscsi_chunk to point to the next
+                         * We set up the iscsi_segment to point to the next
                          * scatterlist entry to copy to. As we go along,
                          * we move on to the next scatterlist entry and
                          * update the digest per-entry.
@@ -774,13 +786,13 @@ iscsi_tcp_hdr_dissect(struct iscsi_conn *conn, struct iscsi_hdr *hdr)
                                   "datalen=%d)\n", tcp_conn,
                                   tcp_ctask->data_offset,
                                   tcp_conn->in.datalen);
-                        return iscsi_chunk_seek_sg(&tcp_conn->in.chunk,
-                                                scsi_sglist(ctask->sc),
-                                                scsi_sg_count(ctask->sc),
-                                                tcp_ctask->data_offset,
-                                                tcp_conn->in.datalen,
-                                                iscsi_tcp_process_data_in,
-                                                rx_hash);
+                        return iscsi_segment_seek_sg(&tcp_conn->in.segment,
+                                                     scsi_sglist(ctask->sc),
+                                                     scsi_sg_count(ctask->sc),
+                                                     tcp_ctask->data_offset,
+                                                     tcp_conn->in.datalen,
+                                                     iscsi_tcp_process_data_in,
+                                                     rx_hash);
                 }
                 /* fall through */
         case ISCSI_OP_SCSI_CMD_RSP:
@@ -846,17 +858,6 @@ iscsi_tcp_hdr_dissect(struct iscsi_conn *conn, struct iscsi_hdr *hdr)
         return rc;
 }
 
-static inline void
-partial_sg_digest_update(struct hash_desc *desc, struct scatterlist *sg,
-                         int offset, int length)
-{
-        struct scatterlist temp;
-
-        sg_init_table(&temp, 1);
-        sg_set_page(&temp, sg_page(sg), length, offset);
-        crypto_hash_update(desc, &temp, length);
-}
-
 /**
  * iscsi_tcp_hdr_recv_done - process PDU header
  *
@@ -866,7 +867,7 @@ partial_sg_digest_update(struct hash_desc *desc, struct scatterlist *sg,
  */
 static int
 iscsi_tcp_hdr_recv_done(struct iscsi_tcp_conn *tcp_conn,
-                        struct iscsi_chunk *chunk)
+                        struct iscsi_segment *segment)
 {
         struct iscsi_conn *conn = tcp_conn->iscsi_conn;
         struct iscsi_hdr *hdr;
@@ -876,7 +877,7 @@ iscsi_tcp_hdr_recv_done(struct iscsi_tcp_conn *tcp_conn,
          * may need to go back to the caller for more.
          */
         hdr = (struct iscsi_hdr *) tcp_conn->in.hdr_buf;
-        if (chunk->copied == sizeof(struct iscsi_hdr) && hdr->hlength) {
+        if (segment->copied == sizeof(struct iscsi_hdr) && hdr->hlength) {
                 /* Bump the header length - the caller will
                  * just loop around and get the AHS for us, and
                  * call again. */
@@ -886,8 +887,8 @@ iscsi_tcp_hdr_recv_done(struct iscsi_tcp_conn *tcp_conn,
                 if (sizeof(*hdr) + ahslen > sizeof(tcp_conn->in.hdr_buf))
                         return ISCSI_ERR_AHSLEN;
 
-                chunk->total_size += ahslen;
-                chunk->size += ahslen;
+                segment->total_size += ahslen;
+                segment->size += ahslen;
                 return 0;
         }
 
@@ -895,16 +896,16 @@ iscsi_tcp_hdr_recv_done(struct iscsi_tcp_conn *tcp_conn,
          * header digests; if so, set up the recv_digest buffer
          * and go back for more. */
         if (conn->hdrdgst_en) {
-                if (chunk->digest_len == 0) {
-                        iscsi_tcp_chunk_splice_digest(chunk,
-                                                      chunk->recv_digest);
+                if (segment->digest_len == 0) {
+                        iscsi_tcp_segment_splice_digest(segment,
+                                                        segment->recv_digest);
                         return 0;
                 }
                 iscsi_tcp_dgst_header(&tcp_conn->rx_hash, hdr,
-                                      chunk->total_copied - ISCSI_DIGEST_SIZE,
-                                      chunk->digest);
+                                      segment->total_copied - ISCSI_DIGEST_SIZE,
+                                      segment->digest);
 
-                if (!iscsi_tcp_dgst_verify(tcp_conn, chunk))
+                if (!iscsi_tcp_dgst_verify(tcp_conn, segment))
                         return ISCSI_ERR_HDR_DGST;
         }
 
@@ -925,7 +926,7 @@ iscsi_tcp_recv(read_descriptor_t *rd_desc, struct sk_buff *skb,
 {
         struct iscsi_conn *conn = rd_desc->arg.data;
         struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
-        struct iscsi_chunk *chunk = &tcp_conn->in.chunk;
+        struct iscsi_segment *segment = &tcp_conn->in.segment;
         struct skb_seq_state seq;
         unsigned int consumed = 0;
         int rc = 0;
@@ -943,27 +944,31 @@ iscsi_tcp_recv(read_descriptor_t *rd_desc, struct sk_buff *skb,
                 const u8 *ptr;
 
                 avail = skb_seq_read(consumed, &ptr, &seq);
-                if (avail == 0)
+                if (avail == 0) {
+                        debug_tcp("no more data avail. Consumed %d\n",
+                                  consumed);
                         break;
-                BUG_ON(chunk->copied >= chunk->size);
+                }
+                BUG_ON(segment->copied >= segment->size);
 
                 debug_tcp("skb %p ptr=%p avail=%u\n", skb, ptr, avail);
-                rc = iscsi_tcp_chunk_recv(tcp_conn, chunk, ptr, avail);
+                rc = iscsi_tcp_segment_recv(tcp_conn, segment, ptr, avail);
                 BUG_ON(rc == 0);
                 consumed += rc;
 
-                if (chunk->total_copied >= chunk->total_size) {
-                        rc = chunk->done(tcp_conn, chunk);
+                if (segment->total_copied >= segment->total_size) {
+                        debug_tcp("segment done\n");
+                        rc = segment->done(tcp_conn, segment);
                         if (rc != 0) {
                                 skb_abort_seq_read(&seq);
                                 goto error;
                         }
 
                         /* The done() functions sets up the
-                         * next chunk. */
+                         * next segment. */
                 }
         }
-
+        skb_abort_seq_read(&seq);
         conn->rxdata_octets += consumed;
         return consumed;
 
@@ -996,7 +1001,7 @@ iscsi_tcp_data_ready(struct sock *sk, int flag)
 
         /* If we had to (atomically) map a highmem page,
          * unmap it now. */
-        iscsi_tcp_chunk_unmap(&tcp_conn->in.chunk);
+        iscsi_tcp_segment_unmap(&tcp_conn->in.segment);
 }
 
 static void
@@ -1076,121 +1081,173 @@ iscsi_conn_restore_callbacks(struct iscsi_tcp_conn *tcp_conn)
 }
 
 /**
- * iscsi_send - generic send routine
- * @sk: kernel's socket
- * @buf: buffer to write from
- * @size: actual size to write
- * @flags: socket's flags
- */
-static inline int
-iscsi_send(struct iscsi_conn *conn, struct iscsi_buf *buf, int size, int flags)
+ * iscsi_xmit - TCP transmit
+ **/
+static int
+iscsi_xmit(struct iscsi_conn *conn)
 {
         struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
-        struct socket *sk = tcp_conn->sock;
-        int offset = buf->sg.offset + buf->sent, res;
+        struct iscsi_segment *segment = &tcp_conn->out.segment;
+        unsigned int consumed = 0;
+        int rc = 0;
 
-        /*
-         * if we got use_sg=0 or are sending something we kmallocd
-         * then we did not have to do kmap (kmap returns page_address)
-         *
-         * if we got use_sg > 0, but had to drop down, we do not
-         * set clustering so this should only happen for that
-         * slab case.
-         */
-        if (buf->use_sendmsg)
-                res = sock_no_sendpage(sk, buf->sg.page, offset, size, flags);
-        else
-                res = tcp_conn->sendpage(sk, buf->sg.page, offset, size, flags);
-
-        if (res >= 0) {
-                conn->txdata_octets += res;
-                buf->sent += res;
-                return res;
+        while (1) {
+                rc = iscsi_tcp_xmit_segment(tcp_conn, segment);
+                if (rc < 0)
+                        goto error;
+                if (rc == 0)
+                        break;
+
+                consumed += rc;
+
+                if (segment->total_copied >= segment->total_size) {
+                        if (segment->done != NULL) {
+                                rc = segment->done(tcp_conn, segment);
+                                if (rc < 0)
+                                        goto error;
+                        }
+                }
         }
 
-        tcp_conn->sendpage_failures_cnt++;
-        if (res == -EAGAIN)
-                res = -ENOBUFS;
-        else
-                iscsi_conn_failure(conn, ISCSI_ERR_CONN_FAILED);
-        return res;
+        debug_tcp("xmit %d bytes\n", consumed);
+
+        conn->txdata_octets += consumed;
+        return consumed;
+
+error:
+        /* Transmit error. We could initiate error recovery
+         * here. */
+        debug_tcp("Error sending PDU, errno=%d\n", rc);
+        iscsi_conn_failure(conn, ISCSI_ERR_CONN_FAILED);
+        return rc;
 }
 
 /**
- * iscsi_sendhdr - send PDU Header via tcp_sendpage()
- * @conn: iscsi connection
- * @buf: buffer to write from
- * @datalen: lenght of data to be sent after the header
- *
- * Notes:
- *      (Tx, Fast Path)
- **/
+ * iscsi_tcp_xmit_qlen - return the number of bytes queued for xmit
+ */
 static inline int
-iscsi_sendhdr(struct iscsi_conn *conn, struct iscsi_buf *buf, int datalen)
+iscsi_tcp_xmit_qlen(struct iscsi_conn *conn)
 {
-        int flags = 0; /* MSG_DONTWAIT; */
-        int res, size;
-
-        size = buf->sg.length - buf->sent;
-        BUG_ON(buf->sent + size > buf->sg.length);
-        if (buf->sent + size != buf->sg.length || datalen)
-                flags |= MSG_MORE;
-
-        res = iscsi_send(conn, buf, size, flags);
-        debug_tcp("sendhdr %d bytes, sent %d res %d\n", size, buf->sent, res);
-        if (res >= 0) {
-                if (size != res)
-                        return -EAGAIN;
-                return 0;
-        }
+        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
+        struct iscsi_segment *segment = &tcp_conn->out.segment;
 
-        return res;
+        return segment->total_copied - segment->total_size;
 }
 
-/**
- * iscsi_sendpage - send one page of iSCSI Data-Out.
- * @conn: iscsi connection
- * @buf: buffer to write from
- * @count: remaining data
- * @sent: number of bytes sent
- *
- * Notes:
- *      (Tx, Fast Path)
- **/
 static inline int
-iscsi_sendpage(struct iscsi_conn *conn, struct iscsi_buf *buf,
-               int *count, int *sent)
+iscsi_tcp_flush(struct iscsi_conn *conn)
 {
-        int flags = 0; /* MSG_DONTWAIT; */
-        int res, size;
-
-        size = buf->sg.length - buf->sent;
-        BUG_ON(buf->sent + size > buf->sg.length);
-        if (size > *count)
-                size = *count;
-        if (buf->sent + size != buf->sg.length || *count != size)
-                flags |= MSG_MORE;
-
-        res = iscsi_send(conn, buf, size, flags);
-        debug_tcp("sendpage: %d bytes, sent %d left %d sent %d res %d\n",
-                  size, buf->sent, *count, *sent, res);
-        if (res >= 0) {
-                *count -= res;
-                *sent += res;
-                if (size != res)
+        int rc;
+
+        while (iscsi_tcp_xmit_qlen(conn)) {
+                rc = iscsi_xmit(conn);
+                if (rc == 0)
                         return -EAGAIN;
-                return 0;
+                if (rc < 0)
+                        return rc;
         }
 
-        return res;
+        return 0;
 }
 
-static inline void
-iscsi_data_digest_init(struct iscsi_tcp_conn *tcp_conn,
-                      struct iscsi_tcp_cmd_task *tcp_ctask)
+/*
+ * This is called when we're done sending the header.
+ * Simply copy the data_segment to the send segment, and return.
+ */
+static int
+iscsi_tcp_send_hdr_done(struct iscsi_tcp_conn *tcp_conn,
+                        struct iscsi_segment *segment)
 {
-        crypto_hash_init(&tcp_conn->tx_hash);
-        tcp_ctask->digest_count = 4;
+        tcp_conn->out.segment = tcp_conn->out.data_segment;
+        debug_tcp("Header done. Next segment size %u total_size %u\n",
+                  tcp_conn->out.segment.size, tcp_conn->out.segment.total_size);
+        return 0;
+}
+
+static void
+iscsi_tcp_send_hdr_prep(struct iscsi_conn *conn, void *hdr, size_t hdrlen)
+{
+        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
+
+        debug_tcp("%s(%p%s)\n", __FUNCTION__, tcp_conn,
+                        conn->hdrdgst_en? ", digest enabled" : "");
+
+        /* Clear the data segment - needs to be filled in by the
+         * caller using iscsi_tcp_send_data_prep() */
+        memset(&tcp_conn->out.data_segment, 0, sizeof(struct iscsi_segment));
+
+        /* If header digest is enabled, compute the CRC and
+         * place the digest into the same buffer. We make
+         * sure that both iscsi_tcp_ctask and mtask have
+         * sufficient room.
+         */
+        if (conn->hdrdgst_en) {
+                iscsi_tcp_dgst_header(&tcp_conn->tx_hash, hdr, hdrlen,
+                                      hdr + hdrlen);
+                hdrlen += ISCSI_DIGEST_SIZE;
+        }
+
+        /* Remember header pointer for later, when we need
+         * to decide whether there's a payload to go along
+         * with the header. */
+        tcp_conn->out.hdr = hdr;
+
+        iscsi_segment_init_linear(&tcp_conn->out.segment, hdr, hdrlen,
+                                iscsi_tcp_send_hdr_done, NULL);
+}
+
+/*
+ * Prepare the send buffer for the payload data.
+ * Padding and checksumming will all be taken care
+ * of by the iscsi_segment routines.
+ */
+static int
+iscsi_tcp_send_data_prep(struct iscsi_conn *conn, struct scatterlist *sg,
+                         unsigned int count, unsigned int offset,
+                         unsigned int len)
+{
+        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
+        struct hash_desc *tx_hash = NULL;
+        unsigned int hdr_spec_len;
+
+        debug_tcp("%s(%p, offset=%d, datalen=%d%s)\n", __FUNCTION__,
+                        tcp_conn, offset, len,
+                        conn->datadgst_en? ", digest enabled" : "");
+
+        /* Make sure the datalen matches what the caller
+           said he would send. */
+        hdr_spec_len = ntoh24(tcp_conn->out.hdr->dlength);
+        WARN_ON(iscsi_padded(len) != iscsi_padded(hdr_spec_len));
+
+        if (conn->datadgst_en)
+                tx_hash = &tcp_conn->tx_hash;
+
+        return iscsi_segment_seek_sg(&tcp_conn->out.data_segment,
+                                   sg, count, offset, len,
+                                   NULL, tx_hash);
+}
+
+static void
+iscsi_tcp_send_linear_data_prepare(struct iscsi_conn *conn, void *data,
+                                   size_t len)
+{
+        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
+        struct hash_desc *tx_hash = NULL;
+        unsigned int hdr_spec_len;
+
+        debug_tcp("%s(%p, datalen=%d%s)\n", __FUNCTION__, tcp_conn, len,
+                  conn->datadgst_en? ", digest enabled" : "");
+
+        /* Make sure the datalen matches what the caller
+           said he would send. */
+        hdr_spec_len = ntoh24(tcp_conn->out.hdr->dlength);
+        WARN_ON(iscsi_padded(len) != iscsi_padded(hdr_spec_len));
+
+        if (conn->datadgst_en)
+                tx_hash = &tcp_conn->tx_hash;
+
+        iscsi_segment_init_linear(&tcp_conn->out.data_segment,
+                                data, len, NULL, tx_hash);
 }
 
 /**
@@ -1206,12 +1263,17 @@ iscsi_data_digest_init(struct iscsi_tcp_conn *tcp_conn,
  *
  *      Called under connection lock.
  **/
-static void
+static int
 iscsi_solicit_data_cont(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask,
-                        struct iscsi_r2t_info *r2t, int left)
+                        struct iscsi_r2t_info *r2t)
 {
         struct iscsi_data *hdr;
-        int new_offset;
+        int new_offset, left;
+
+        BUG_ON(r2t->data_length - r2t->sent < 0);
+        left = r2t->data_length - r2t->sent;
+        if (left == 0)
+                return 0;
 
         hdr = &r2t->dtask.hdr;
         memset(hdr, 0, sizeof(struct iscsi_data));
@@ -1232,43 +1294,46 @@ iscsi_solicit_data_cont(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask,
                 r2t->data_count = left;
                 hdr->flags = ISCSI_FLAG_CMD_FINAL;
         }
-        conn->dataout_pdus_cnt++;
-
-        iscsi_buf_init_iov(&r2t->headbuf, (char*)hdr,
-                           sizeof(struct iscsi_hdr));
-
-        if (iscsi_buf_left(&r2t->sendbuf))
-                return;
-
-        iscsi_buf_init_sg(&r2t->sendbuf, r2t->sg);
-        r2t->sg += 1;
-}
-
-static void iscsi_set_padding(struct iscsi_tcp_cmd_task *tcp_ctask,
-                              unsigned long len)
-{
-        tcp_ctask->pad_count = len & (ISCSI_PAD_LEN - 1);
-        if (!tcp_ctask->pad_count)
-                return;
 
-        tcp_ctask->pad_count = ISCSI_PAD_LEN - tcp_ctask->pad_count;
-        debug_scsi("write padding %d bytes\n", tcp_ctask->pad_count);
-        tcp_ctask->xmstate |= XMSTATE_W_PAD;
+        conn->dataout_pdus_cnt++;
+        return 1;
 }
 
 /**
- * iscsi_tcp_cmd_init - Initialize iSCSI SCSI_READ or SCSI_WRITE commands
+ * iscsi_tcp_ctask - Initialize iSCSI SCSI_READ or SCSI_WRITE commands
  * @conn: iscsi connection
  * @ctask: scsi command task
  * @sc: scsi command
  **/
-static void
-iscsi_tcp_cmd_init(struct iscsi_cmd_task *ctask)
+static int
+iscsi_tcp_ctask_init(struct iscsi_cmd_task *ctask)
 {
         struct iscsi_tcp_cmd_task *tcp_ctask = ctask->dd_data;
+        struct iscsi_conn *conn = ctask->conn;
+        struct scsi_cmnd *sc = ctask->sc;
+        int err;
 
         BUG_ON(__kfifo_len(tcp_ctask->r2tqueue));
-        tcp_ctask->xmstate = XMSTATE_CMD_HDR_INIT;
+        tcp_ctask->sent = 0;
+        tcp_ctask->exp_datasn = 0;
+
+        /* Prepare PDU, optionally w/ immediate data */
+        debug_scsi("ctask deq [cid %d itt 0x%x imm %d unsol %d]\n",
+                    conn->id, ctask->itt, ctask->imm_count,
+                    ctask->unsol_count);
+        iscsi_tcp_send_hdr_prep(conn, ctask->hdr, ctask->hdr_len);
+
+        if (!ctask->imm_count)
+                return 0;
+
+        /* If we have immediate data, attach a payload */
+        err = iscsi_tcp_send_data_prep(conn, scsi_sglist(sc), scsi_sg_count(sc),
+                                       0, ctask->imm_count);
+        if (err)
+                return err;
+        tcp_ctask->sent += ctask->imm_count;
+        ctask->imm_count = 0;
+        return 0;
 }
 
 /**
@@ -1280,71 +1345,17 @@ iscsi_tcp_cmd_init(struct iscsi_cmd_task *ctask)
  *      The function can return -EAGAIN in which case caller must
  *      call it again later, or recover. '0' return code means successful
  *      xmit.
- *
- *      Management xmit state machine consists of these states:
- *              XMSTATE_IMM_HDR_INIT    - calculate digest of PDU Header
- *              XMSTATE_IMM_HDR         - PDU Header xmit in progress
- *              XMSTATE_IMM_DATA        - PDU Data xmit in progress
- *              XMSTATE_IDLE            - management PDU is done
  **/
 static int
 iscsi_tcp_mtask_xmit(struct iscsi_conn *conn, struct iscsi_mgmt_task *mtask)
 {
-        struct iscsi_tcp_mgmt_task *tcp_mtask = mtask->dd_data;
         int rc;
 
-        debug_scsi("mtask deq [cid %d state %x itt 0x%x]\n",
-                conn->id, tcp_mtask->xmstate, mtask->itt);
-
-        if (tcp_mtask->xmstate & XMSTATE_IMM_HDR_INIT) {
-                iscsi_buf_init_iov(&tcp_mtask->headbuf, (char*)mtask->hdr,
-                                   sizeof(struct iscsi_hdr));
-
-                if (mtask->data_count) {
-                        tcp_mtask->xmstate |= XMSTATE_IMM_DATA;
-                        iscsi_buf_init_iov(&tcp_mtask->sendbuf,
-                                           (char*)mtask->data,
-                                           mtask->data_count);
-                }
-
-                if (conn->c_stage != ISCSI_CONN_INITIAL_STAGE &&
-                    conn->stop_stage != STOP_CONN_RECOVER &&
-                    conn->hdrdgst_en)
-                        iscsi_hdr_digest(conn, &tcp_mtask->headbuf,
-                                        (u8*)tcp_mtask->hdrext);
-
-                tcp_mtask->sent = 0;
-                tcp_mtask->xmstate &= ~XMSTATE_IMM_HDR_INIT;
-                tcp_mtask->xmstate |= XMSTATE_IMM_HDR;
-        }
-
-        if (tcp_mtask->xmstate & XMSTATE_IMM_HDR) {
-                rc = iscsi_sendhdr(conn, &tcp_mtask->headbuf,
-                                   mtask->data_count);
-                if (rc)
-                        return rc;
-                tcp_mtask->xmstate &= ~XMSTATE_IMM_HDR;
-        }
-
-        if (tcp_mtask->xmstate & XMSTATE_IMM_DATA) {
-                BUG_ON(!mtask->data_count);
-                tcp_mtask->xmstate &= ~XMSTATE_IMM_DATA;
-                /* FIXME: implement.
-                 * Virtual buffer could be spreaded across multiple pages...
-                 */
-                do {
-                        int rc;
-
-                        rc = iscsi_sendpage(conn, &tcp_mtask->sendbuf,
-                                        &mtask->data_count, &tcp_mtask->sent);
-                        if (rc) {
-                                tcp_mtask->xmstate |= XMSTATE_IMM_DATA;
-                                return rc;
-                        }
-                } while (mtask->data_count);
-        }
+        /* Flush any pending data first. */
+        rc = iscsi_tcp_flush(conn);
+        if (rc < 0)
+                return rc;
 
-        BUG_ON(tcp_mtask->xmstate != XMSTATE_IDLE);
         if (mtask->hdr->itt == RESERVED_ITT) {
                 struct iscsi_session *session = conn->session;
 
@@ -1352,411 +1363,112 @@ iscsi_tcp_mtask_xmit(struct iscsi_conn *conn, struct iscsi_mgmt_task *mtask)
                 iscsi_free_mgmt_task(conn, mtask);
                 spin_unlock_bh(&session->lock);
         }
+
         return 0;
 }
 
+/*
+ * iscsi_tcp_ctask_xmit - xmit normal PDU task
+ * @conn: iscsi connection
+ * @ctask: iscsi command task
+ *
+ * We're expected to return 0 when everything was transmitted succesfully,
+ * -EAGAIN if there's still data in the queue, or != 0 for any other kind
+ * of error.
+ */
 static int
-iscsi_send_cmd_hdr(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
+iscsi_tcp_ctask_xmit(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
 {
-        struct scsi_cmnd *sc = ctask->sc;
         struct iscsi_tcp_cmd_task *tcp_ctask = ctask->dd_data;
+        struct scsi_cmnd *sc = ctask->sc;
         int rc = 0;
 
-        if (tcp_ctask->xmstate & XMSTATE_CMD_HDR_INIT) {
-                tcp_ctask->sent = 0;
-                tcp_ctask->sg_count = 0;
-                tcp_ctask->exp_datasn = 0;
-
-                if (sc->sc_data_direction == DMA_TO_DEVICE) {
-                        struct scatterlist *sg = scsi_sglist(sc);
-
-                        iscsi_buf_init_sg(&tcp_ctask->sendbuf, sg);
-                        tcp_ctask->sg = sg + 1;
-                        tcp_ctask->bad_sg = sg + scsi_sg_count(sc);
-
-                        debug_scsi("cmd [itt 0x%x total %d imm_data %d "
-                                   "unsol count %d, unsol offset %d]\n",
-                                   ctask->itt, scsi_bufflen(sc),
-                                   ctask->imm_count, ctask->unsol_count,
-                                   ctask->unsol_offset);
-                }
-
-                iscsi_buf_init_iov(&tcp_ctask->headbuf, (char*)ctask->hdr,
-                                  ctask->hdr_len);
-
-                if (conn->hdrdgst_en)
-                        iscsi_hdr_digest(conn, &tcp_ctask->headbuf,
-                                         iscsi_next_hdr(ctask));
-                tcp_ctask->xmstate &= ~XMSTATE_CMD_HDR_INIT;
-                tcp_ctask->xmstate |= XMSTATE_CMD_HDR_XMIT;
-        }
-
-        if (tcp_ctask->xmstate & XMSTATE_CMD_HDR_XMIT) {
-                rc = iscsi_sendhdr(conn, &tcp_ctask->headbuf, ctask->imm_count);
-                if (rc)
-                        return rc;
-                tcp_ctask->xmstate &= ~XMSTATE_CMD_HDR_XMIT;
-
-                if (sc->sc_data_direction != DMA_TO_DEVICE)
-                        return 0;
-
-                if (ctask->imm_count) {
-                        tcp_ctask->xmstate |= XMSTATE_IMM_DATA;
-                        iscsi_set_padding(tcp_ctask, ctask->imm_count);
-
-                        if (ctask->conn->datadgst_en) {
-                                iscsi_data_digest_init(ctask->conn->dd_data,
-                                                       tcp_ctask);
-                                tcp_ctask->immdigest = 0;
-                        }
-                }
-
-                if (ctask->unsol_count)
-                        tcp_ctask->xmstate |=
-                                        XMSTATE_UNS_HDR | XMSTATE_UNS_INIT;
-        }
-        return rc;
-}
-
-static int
-iscsi_send_padding(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
-{
-        struct iscsi_tcp_cmd_task *tcp_ctask = ctask->dd_data;
-        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
-        int sent = 0, rc;
-
-        if (tcp_ctask->xmstate & XMSTATE_W_PAD) {
-                iscsi_buf_init_iov(&tcp_ctask->sendbuf, (char*)&tcp_ctask->pad,
-                                   tcp_ctask->pad_count);
-                if (conn->datadgst_en)
-                        crypto_hash_update(&tcp_conn->tx_hash,
-                                           &tcp_ctask->sendbuf.sg,
-                                           tcp_ctask->sendbuf.sg.length);
-        } else if (!(tcp_ctask->xmstate & XMSTATE_W_RESEND_PAD))
-                return 0;
-
-        tcp_ctask->xmstate &= ~XMSTATE_W_PAD;
-        tcp_ctask->xmstate &= ~XMSTATE_W_RESEND_PAD;
-        debug_scsi("sending %d pad bytes for itt 0x%x\n",
-                   tcp_ctask->pad_count, ctask->itt);
-        rc = iscsi_sendpage(conn, &tcp_ctask->sendbuf, &tcp_ctask->pad_count,
-                           &sent);
-        if (rc) {
-                debug_scsi("padding send failed %d\n", rc);
-                tcp_ctask->xmstate |= XMSTATE_W_RESEND_PAD;
-        }
-        return rc;
-}
-
-static int
-iscsi_send_digest(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask,
-                        struct iscsi_buf *buf, uint32_t *digest)
-{
-        struct iscsi_tcp_cmd_task *tcp_ctask;
-        struct iscsi_tcp_conn *tcp_conn;
-        int rc, sent = 0;
-
-        if (!conn->datadgst_en)
-                return 0;
-
-        tcp_ctask = ctask->dd_data;
-        tcp_conn = conn->dd_data;
-
-        if (!(tcp_ctask->xmstate & XMSTATE_W_RESEND_DATA_DIGEST)) {
-                crypto_hash_final(&tcp_conn->tx_hash, (u8*)digest);
-                iscsi_buf_init_iov(buf, (char*)digest, 4);
-        }
-        tcp_ctask->xmstate &= ~XMSTATE_W_RESEND_DATA_DIGEST;
-
-        rc = iscsi_sendpage(conn, buf, &tcp_ctask->digest_count, &sent);
-        if (!rc)
-                debug_scsi("sent digest 0x%x for itt 0x%x\n", *digest,
-                          ctask->itt);
-        else {
-                debug_scsi("sending digest 0x%x failed for itt 0x%x!\n",
-                          *digest, ctask->itt);
-                tcp_ctask->xmstate |= XMSTATE_W_RESEND_DATA_DIGEST;
-        }
-        return rc;
-}
-
-static int
-iscsi_send_data(struct iscsi_cmd_task *ctask, struct iscsi_buf *sendbuf,
-                struct scatterlist **sg, int *sent, int *count,
-                struct iscsi_buf *digestbuf, uint32_t *digest)
-{
-        struct iscsi_tcp_cmd_task *tcp_ctask = ctask->dd_data;
-        struct iscsi_conn *conn = ctask->conn;
-        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
-        int rc, buf_sent, offset;
-
-        while (*count) {
-                buf_sent = 0;
-                offset = sendbuf->sent;
-
-                rc = iscsi_sendpage(conn, sendbuf, count, &buf_sent);
-                *sent = *sent + buf_sent;
-                if (buf_sent && conn->datadgst_en)
-                        partial_sg_digest_update(&tcp_conn->tx_hash,
-                                &sendbuf->sg, sendbuf->sg.offset + offset,
-                                buf_sent);
-                if (!iscsi_buf_left(sendbuf) && *sg != tcp_ctask->bad_sg) {
-                        iscsi_buf_init_sg(sendbuf, *sg);
-                        *sg = *sg + 1;
-                }
-
-                if (rc)
-                        return rc;
-        }
-
-        rc = iscsi_send_padding(conn, ctask);
-        if (rc)
+flush:
+        /* Flush any pending data first. */
+        rc = iscsi_tcp_flush(conn);
+        if (rc < 0)
                 return rc;
 
-        return iscsi_send_digest(conn, ctask, digestbuf, digest);
-}
-
-static int
-iscsi_send_unsol_hdr(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
-{
-        struct iscsi_tcp_cmd_task *tcp_ctask = ctask->dd_data;
-        struct iscsi_data_task *dtask;
-        int rc;
-
-        tcp_ctask->xmstate |= XMSTATE_UNS_DATA;
-        if (tcp_ctask->xmstate & XMSTATE_UNS_INIT) {
-                dtask = &tcp_ctask->unsol_dtask;
-
-                iscsi_prep_unsolicit_data_pdu(ctask, &dtask->hdr);
-                iscsi_buf_init_iov(&tcp_ctask->headbuf, (char*)&dtask->hdr,
-                                   sizeof(struct iscsi_hdr));
-                if (conn->hdrdgst_en)
-                        iscsi_hdr_digest(conn, &tcp_ctask->headbuf,
-                                        (u8*)dtask->hdrext);
-
-                tcp_ctask->xmstate &= ~XMSTATE_UNS_INIT;
-                iscsi_set_padding(tcp_ctask, ctask->data_count);
-        }
-
-        rc = iscsi_sendhdr(conn, &tcp_ctask->headbuf, ctask->data_count);
-        if (rc) {
-                tcp_ctask->xmstate &= ~XMSTATE_UNS_DATA;
-                tcp_ctask->xmstate |= XMSTATE_UNS_HDR;
-                return rc;
-        }
+        /* Are we done already? */
+        if (sc->sc_data_direction != DMA_TO_DEVICE)
+                return 0;
 
-        if (conn->datadgst_en) {
-                dtask = &tcp_ctask->unsol_dtask;
-                iscsi_data_digest_init(ctask->conn->dd_data, tcp_ctask);
-                dtask->digest = 0;
-        }
+        if (ctask->unsol_count != 0) {
+                struct iscsi_data *hdr = &tcp_ctask->unsol_dtask.hdr;
 
-        debug_scsi("uns dout [itt 0x%x dlen %d sent %d]\n",
-                   ctask->itt, ctask->unsol_count, tcp_ctask->sent);
-        return 0;
-}
+                /* Prepare a header for the unsolicited PDU.
+                 * The amount of data we want to send will be
+                 * in ctask->data_count.
+                 * FIXME: return the data count instead.
+                 */
+                iscsi_prep_unsolicit_data_pdu(ctask, hdr);
 
-static int
-iscsi_send_unsol_pdu(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
-{
-        struct iscsi_tcp_cmd_task *tcp_ctask = ctask->dd_data;
-        int rc;
+                debug_tcp("unsol dout [itt 0x%x doff %d dlen %d]\n",
+                                ctask->itt, tcp_ctask->sent, ctask->data_count);
 
-        if (tcp_ctask->xmstate & XMSTATE_UNS_HDR) {
-                BUG_ON(!ctask->unsol_count);
-                tcp_ctask->xmstate &= ~XMSTATE_UNS_HDR;
-send_hdr:
-                rc = iscsi_send_unsol_hdr(conn, ctask);
+                iscsi_tcp_send_hdr_prep(conn, hdr, sizeof(*hdr));
+                rc = iscsi_tcp_send_data_prep(conn, scsi_sglist(sc),
+                                              scsi_sg_count(sc),
+                                              tcp_ctask->sent,
+                                              ctask->data_count);
                 if (rc)
-                        return rc;
-        }
-
-        if (tcp_ctask->xmstate & XMSTATE_UNS_DATA) {
-                struct iscsi_data_task *dtask = &tcp_ctask->unsol_dtask;
-                int start = tcp_ctask->sent;
+                        goto fail;
+                tcp_ctask->sent += ctask->data_count;
+                ctask->unsol_count -= ctask->data_count;
+                goto flush;
+        } else {
+                struct iscsi_session *session = conn->session;
+                struct iscsi_r2t_info *r2t;
 
-                rc = iscsi_send_data(ctask, &tcp_ctask->sendbuf, &tcp_ctask->sg,
-                                     &tcp_ctask->sent, &ctask->data_count,
-                                     &dtask->digestbuf, &dtask->digest);
-                ctask->unsol_count -= tcp_ctask->sent - start;
-                if (rc)
-                        return rc;
-                tcp_ctask->xmstate &= ~XMSTATE_UNS_DATA;
-                /*
-                 * Done with the Data-Out. Next, check if we need
-                 * to send another unsolicited Data-Out.
+                /* All unsolicited PDUs sent. Check for solicited PDUs.
                  */
-                if (ctask->unsol_count) {
-                        debug_scsi("sending more uns\n");
-                        tcp_ctask->xmstate |= XMSTATE_UNS_INIT;
-                        goto send_hdr;
+                spin_lock_bh(&session->lock);
+                r2t = tcp_ctask->r2t;
+                if (r2t != NULL) {
+                        /* Continue with this R2T? */
+                        if (!iscsi_solicit_data_cont(conn, ctask, r2t)) {
+                                debug_scsi("  done with r2t %p\n", r2t);
+
+                                __kfifo_put(tcp_ctask->r2tpool.queue,
+                                            (void*)&r2t, sizeof(void*));
+                                tcp_ctask->r2t = r2t = NULL;
+                        }
                 }
-        }
-        return 0;
-}
 
-static int iscsi_send_sol_pdu(struct iscsi_conn *conn,
-                              struct iscsi_cmd_task *ctask)
-{
-        struct iscsi_tcp_cmd_task *tcp_ctask = ctask->dd_data;
-        struct iscsi_session *session = conn->session;
-        struct iscsi_r2t_info *r2t;
-        struct iscsi_data_task *dtask;
-        int left, rc;
-
-        if (tcp_ctask->xmstate & XMSTATE_SOL_HDR_INIT) {
-                if (!tcp_ctask->r2t) {
-                        spin_lock_bh(&session->lock);
+                if (r2t == NULL) {
                         __kfifo_get(tcp_ctask->r2tqueue, (void*)&tcp_ctask->r2t,
                                     sizeof(void*));
-                        spin_unlock_bh(&session->lock);
+                        r2t = tcp_ctask->r2t;
                 }
-send_hdr:
-                r2t = tcp_ctask->r2t;
-                dtask = &r2t->dtask;
-
-                if (conn->hdrdgst_en)
-                        iscsi_hdr_digest(conn, &r2t->headbuf,
-                                        (u8*)dtask->hdrext);
-                tcp_ctask->xmstate &= ~XMSTATE_SOL_HDR_INIT;
-                tcp_ctask->xmstate |= XMSTATE_SOL_HDR;
-        }
-
-        if (tcp_ctask->xmstate & XMSTATE_SOL_HDR) {
-                r2t = tcp_ctask->r2t;
-                dtask = &r2t->dtask;
-
-                rc = iscsi_sendhdr(conn, &r2t->headbuf, r2t->data_count);
-                if (rc)
-                        return rc;
-                tcp_ctask->xmstate &= ~XMSTATE_SOL_HDR;
-                tcp_ctask->xmstate |= XMSTATE_SOL_DATA;
+                spin_unlock_bh(&session->lock);
 
-                if (conn->datadgst_en) {
-                        iscsi_data_digest_init(conn->dd_data, tcp_ctask);
-                        dtask->digest = 0;
+                /* Waiting for more R2Ts to arrive. */
+                if (r2t == NULL) {
+                        debug_tcp("no R2Ts yet\n");
+                        return 0;
                 }
 
-                iscsi_set_padding(tcp_ctask, r2t->data_count);
-                debug_scsi("sol dout [dsn %d itt 0x%x dlen %d sent %d]\n",
-                        r2t->solicit_datasn - 1, ctask->itt, r2t->data_count,
-                        r2t->sent);
-        }
+                debug_scsi("sol dout %p [dsn %d itt 0x%x doff %d dlen %d]\n",
+                        r2t, r2t->solicit_datasn - 1, ctask->itt,
+                        r2t->data_offset + r2t->sent, r2t->data_count);
 
-        if (tcp_ctask->xmstate & XMSTATE_SOL_DATA) {
-                r2t = tcp_ctask->r2t;
-                dtask = &r2t->dtask;
+                iscsi_tcp_send_hdr_prep(conn, &r2t->dtask.hdr,
+                                        sizeof(struct iscsi_hdr));
 
-                rc = iscsi_send_data(ctask, &r2t->sendbuf, &r2t->sg,
-                                     &r2t->sent, &r2t->data_count,
-                                     &dtask->digestbuf, &dtask->digest);
+                rc = iscsi_tcp_send_data_prep(conn, scsi_sglist(sc),
+                                              scsi_sg_count(sc),
+                                              r2t->data_offset + r2t->sent,
+                                              r2t->data_count);
                 if (rc)
-                        return rc;
-                tcp_ctask->xmstate &= ~XMSTATE_SOL_DATA;
-
-                /*
-                 * Done with this Data-Out. Next, check if we have
-                 * to send another Data-Out for this R2T.
-                 */
-                BUG_ON(r2t->data_length - r2t->sent < 0);
-                left = r2t->data_length - r2t->sent;
-                if (left) {
-                        iscsi_solicit_data_cont(conn, ctask, r2t, left);
-                        goto send_hdr;
-                }
-
-                /*
-                 * Done with this R2T. Check if there are more
-                 * outstanding R2Ts ready to be processed.
-                 */
-                spin_lock_bh(&session->lock);
-                tcp_ctask->r2t = NULL;
-                __kfifo_put(tcp_ctask->r2tpool.queue, (void*)&r2t,
-                            sizeof(void*));
-                if (__kfifo_get(tcp_ctask->r2tqueue, (void*)&r2t,
-                                sizeof(void*))) {
-                        tcp_ctask->r2t = r2t;
-                        spin_unlock_bh(&session->lock);
-                        goto send_hdr;
-                }
-                spin_unlock_bh(&session->lock);
+                        goto fail;
+                tcp_ctask->sent += r2t->data_count;
+                r2t->sent += r2t->data_count;
+                goto flush;
         }
         return 0;
-}
-
-/**
- * iscsi_tcp_ctask_xmit - xmit normal PDU task
- * @conn: iscsi connection
- * @ctask: iscsi command task
- *
- * Notes:
- *      The function can return -EAGAIN in which case caller must
- *      call it again later, or recover. '0' return code means successful
- *      xmit.
- *      The function is devided to logical helpers (above) for the different
- *      xmit stages.
- *
- *iscsi_send_cmd_hdr()
- *      XMSTATE_CMD_HDR_INIT - prepare Header and Data buffers Calculate
- *                             Header Digest
- *      XMSTATE_CMD_HDR_XMIT - Transmit header in progress
- *
- *iscsi_send_padding
- *      XMSTATE_W_PAD        - Prepare and send pading
- *      XMSTATE_W_RESEND_PAD - retry send pading
- *
- *iscsi_send_digest
- *      XMSTATE_W_RESEND_DATA_DIGEST - Finalize and send Data Digest
- *      XMSTATE_W_RESEND_DATA_DIGEST - retry sending digest
- *
- *iscsi_send_unsol_hdr
- *      XMSTATE_UNS_INIT     - prepare un-solicit data header and digest
- *      XMSTATE_UNS_HDR      - send un-solicit header
- *
- *iscsi_send_unsol_pdu
- *      XMSTATE_UNS_DATA     - send un-solicit data in progress
- *
- *iscsi_send_sol_pdu
- *      XMSTATE_SOL_HDR_INIT - solicit data header and digest initialize
- *      XMSTATE_SOL_HDR      - send solicit header
- *      XMSTATE_SOL_DATA     - send solicit data
- *
- *iscsi_tcp_ctask_xmit
- *      XMSTATE_IMM_DATA     - xmit managment data (??)
- **/
-static int
-iscsi_tcp_ctask_xmit(struct iscsi_conn *conn, struct iscsi_cmd_task *ctask)
-{
-        struct iscsi_tcp_cmd_task *tcp_ctask = ctask->dd_data;
-        int rc = 0;
-
-        debug_scsi("ctask deq [cid %d xmstate %x itt 0x%x]\n",
-                conn->id, tcp_ctask->xmstate, ctask->itt);
-
-        rc = iscsi_send_cmd_hdr(conn, ctask);
-        if (rc)
-                return rc;
-        if (ctask->sc->sc_data_direction != DMA_TO_DEVICE)
-                return 0;
-
-        if (tcp_ctask->xmstate & XMSTATE_IMM_DATA) {
-                rc = iscsi_send_data(ctask, &tcp_ctask->sendbuf, &tcp_ctask->sg,
-                                     &tcp_ctask->sent, &ctask->imm_count,
-                                     &tcp_ctask->immbuf, &tcp_ctask->immdigest);
-                if (rc)
-                        return rc;
-                tcp_ctask->xmstate &= ~XMSTATE_IMM_DATA;
-        }
-
-        rc = iscsi_send_unsol_pdu(conn, ctask);
-        if (rc)
-                return rc;
-
-        rc = iscsi_send_sol_pdu(conn, ctask);
-        if (rc)
-                return rc;
-
-        return rc;
+fail:
+        iscsi_conn_failure(conn, rc);
+        return -EIO;
 }
 
 static struct iscsi_cls_conn *
@@ -1970,10 +1682,17 @@ free_socket:
 
 /* called with host lock */
 static void
-iscsi_tcp_mgmt_init(struct iscsi_conn *conn, struct iscsi_mgmt_task *mtask)
+iscsi_tcp_mtask_init(struct iscsi_conn *conn, struct iscsi_mgmt_task *mtask)
 {
-        struct iscsi_tcp_mgmt_task *tcp_mtask = mtask->dd_data;
-        tcp_mtask->xmstate = XMSTATE_IMM_HDR_INIT;
+        debug_scsi("mtask deq [cid %d itt 0x%x]\n", conn->id, mtask->itt);
+
+        /* Prepare PDU, optionally w/ immediate data */
+        iscsi_tcp_send_hdr_prep(conn, mtask->hdr, sizeof(*mtask->hdr));
+
+        /* If we have immediate data, attach a payload */
+        if (mtask->data_count)
+                iscsi_tcp_send_linear_data_prepare(conn, mtask->data,
+                                                   mtask->data_count);
 }
 
 static int
@@ -2177,7 +1896,7 @@ iscsi_tcp_session_create(struct iscsi_transport *iscsit,
                 struct iscsi_mgmt_task *mtask = session->mgmt_cmds[cmd_i];
                 struct iscsi_tcp_mgmt_task *tcp_mtask = mtask->dd_data;
 
-                mtask->hdr = &tcp_mtask->hdr;
+                mtask->hdr = (struct iscsi_hdr *) &tcp_mtask->hdr;
         }
 
         if (iscsi_r2tpool_alloc(class_to_transport_session(cls_session)))
@@ -2274,8 +1993,8 @@ static struct iscsi_transport iscsi_tcp_transport = {
         /* IO */
         .send_pdu               = iscsi_conn_send_pdu,
         .get_stats              = iscsi_conn_get_stats,
-        .init_cmd_task          = iscsi_tcp_cmd_init,
-        .init_mgmt_task         = iscsi_tcp_mgmt_init,
+        .init_cmd_task          = iscsi_tcp_ctask_init,
+        .init_mgmt_task         = iscsi_tcp_mtask_init,
         .xmit_cmd_task          = iscsi_tcp_ctask_xmit,
         .xmit_mgmt_task         = iscsi_tcp_mtask_xmit,
         .cleanup_cmd_task       = iscsi_tcp_cleanup_ctask,