[SCSI] implement scsi_data_buffer

In preparation for bidi we abstract all IO members of scsi_cmnd,
that will need to duplicate, into a substructure.

- Group all IO members of scsi_cmnd into a scsi_data_buffer
  structure.
- Adjust accessors to new members.
- scsi_{alloc,free}_sgtable receive a scsi_data_buffer instead of
  scsi_cmnd. And work on it.
- Adjust scsi_init_io() and  scsi_release_buffers() for above
  change.
- Fix other parts of scsi_lib/scsi.c to members migration. Use
  accessors where appropriate.

- fix Documentation about scsi_cmnd in scsi_host.h

- scsi_error.c
  * Changed needed members of struct scsi_eh_save.
  * Careful considerations in scsi_eh_prep/restore_cmnd.

- sd.c and sr.c
  * sd and sr would adjust IO size to align on device's block
    size so code needs to change once we move to scsi_data_buff
    implementation.
  * Convert code to use scsi_for_each_sg
  * Use data accessors where appropriate.

- tgt: convert libsrp to use scsi_data_buffer

- isd200: This driver still bangs on scsi_cmnd IO members,
  so need changing

[jejb: rebased on top of sg_table patches fixed up conflicts
and used the synergy to eliminate use_sg and sg_count]

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 25 insertions, 38 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 69fd62183bab..d5e77e9b3a9c 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -440,7 +440,7 @@ EXPORT_SYMBOL_GPL(scsi_execute_async);
 static void scsi_init_cmd_errh(struct scsi_cmnd *cmd)
 {
         cmd->serial_number = 0;
-        cmd->resid = 0;
+        scsi_set_resid(cmd, 0);
         memset(cmd->sense_buffer, 0, SCSI_SENSE_BUFFERSIZE);
         if (cmd->cmd_len == 0)
                 cmd->cmd_len = COMMAND_SIZE(cmd->cmnd[0]);
@@ -746,25 +746,25 @@ static struct scatterlist *scsi_sg_alloc(unsigned int nents, gfp_t gfp_mask)
         return mempool_alloc(sgp->pool, gfp_mask);
 }
 
-static int scsi_alloc_sgtable(struct scsi_cmnd *cmd, gfp_t gfp_mask)
+static int scsi_alloc_sgtable(struct scsi_data_buffer *sdb, int nents,
+                              gfp_t gfp_mask)
 {
         int ret;
 
-        BUG_ON(!cmd->use_sg);
+        BUG_ON(!nents);
 
-        ret = __sg_alloc_table(&cmd->sg_table, cmd->use_sg,
-                               SCSI_MAX_SG_SEGMENTS, gfp_mask, scsi_sg_alloc);
+        ret = __sg_alloc_table(&sdb->table, nents, SCSI_MAX_SG_SEGMENTS,
+                               gfp_mask, scsi_sg_alloc);
         if (unlikely(ret))
-                __sg_free_table(&cmd->sg_table, SCSI_MAX_SG_SEGMENTS,
+                __sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS,
                                 scsi_sg_free);
 
-        cmd->request_buffer = cmd->sg_table.sgl;
         return ret;
 }
 
-static void scsi_free_sgtable(struct scsi_cmnd *cmd)
+static void scsi_free_sgtable(struct scsi_data_buffer *sdb)
 {
-        __sg_free_table(&cmd->sg_table, SCSI_MAX_SG_SEGMENTS, scsi_sg_free);
+        __sg_free_table(&sdb->table, SCSI_MAX_SG_SEGMENTS, scsi_sg_free);
 }
 
 /*
@@ -786,15 +786,10 @@ static void scsi_free_sgtable(struct scsi_cmnd *cmd)
  */
 void scsi_release_buffers(struct scsi_cmnd *cmd)
 {
-        if (cmd->use_sg)
-                scsi_free_sgtable(cmd);
+        if (cmd->sdb.table.nents)
+                scsi_free_sgtable(&cmd->sdb);
 
-        /*
-         * Zero these out.  They now point to freed memory, and it is
-         * dangerous to hang onto the pointers.
-         */
-        cmd->request_buffer = NULL;
-        cmd->request_bufflen = 0;
+        memset(&cmd->sdb, 0, sizeof(cmd->sdb));
 }
 EXPORT_SYMBOL(scsi_release_buffers);
 
@@ -829,7 +824,7 @@ EXPORT_SYMBOL(scsi_release_buffers);
 void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
 {
         int result = cmd->result;
-        int this_count = cmd->request_bufflen;
+        int this_count = scsi_bufflen(cmd);
         struct request_queue *q = cmd->device->request_queue;
         struct request *req = cmd->request;
         int clear_errors = 1;
@@ -837,8 +832,6 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
         int sense_valid = 0;
         int sense_deferred = 0;
 
-        scsi_release_buffers(cmd);
-
         if (result) {
                 sense_valid = scsi_command_normalize_sense(cmd, &sshdr);
                 if (sense_valid)
@@ -861,9 +854,11 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
                                 req->sense_len = len;
                         }
                 }
-                req->data_len = cmd->resid;
+                req->data_len = scsi_get_resid(cmd);
         }
 
+        scsi_release_buffers(cmd);
+
         /*
          * Next deal with any sectors which we were able to correctly
          * handle.
@@ -871,7 +866,6 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
         SCSI_LOG_HLCOMPLETE(1, printk("%ld sectors total, "
                                       "%d bytes done.\n",
                                       req->nr_sectors, good_bytes));
-        SCSI_LOG_HLCOMPLETE(1, printk("use_sg is %d\n", cmd->use_sg));
 
         if (clear_errors)
                 req->errors = 0;
@@ -1002,35 +996,30 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
 {
         struct request     *req = cmd->request;
         int                count;
-
-        /*
-         * We used to not use scatter-gather for single segment request,
-         * but now we do (it makes highmem I/O easier to support without
-         * kmapping pages)
-         */
-        cmd->use_sg = req->nr_phys_segments;
+        struct scsi_data_buffer *sdb = &cmd->sdb;
 
         /*
          * If sg table allocation fails, requeue request later.
          */
-        if (unlikely(scsi_alloc_sgtable(cmd, gfp_mask))) {
+        if (unlikely(scsi_alloc_sgtable(sdb, req->nr_phys_segments,
+                                        gfp_mask))) {
                 scsi_unprep_request(req);
                 return BLKPREP_DEFER;
         }
 
         req->buffer = NULL;
         if (blk_pc_request(req))
-                cmd->request_bufflen = req->data_len;
+                sdb->length = req->data_len;
         else
-                cmd->request_bufflen = req->nr_sectors << 9;
+                sdb->length = req->nr_sectors << 9;
 
         /* 
          * Next, walk the list, and fill in the addresses and sizes of
          * each segment.
          */
-        count = blk_rq_map_sg(req->q, req, cmd->request_buffer);
-        BUG_ON(count > cmd->use_sg);
-        cmd->use_sg = count;
+        count = blk_rq_map_sg(req->q, req, sdb->table.sgl);
+        BUG_ON(count > sdb->table.nents);
+        sdb->table.nents = count;
         return BLKPREP_OK;
 }
 EXPORT_SYMBOL(scsi_init_io);
@@ -1086,9 +1075,7 @@ int scsi_setup_blk_pc_cmnd(struct scsi_device *sdev, struct request *req)
                 BUG_ON(req->data_len);
                 BUG_ON(req->data);
 
-                cmd->request_bufflen = 0;
-                cmd->request_buffer = NULL;
-                cmd->use_sg = 0;
+                memset(&cmd->sdb, 0, sizeof(cmd->sdb));
                 req->buffer = NULL;
         }