[SCSI] bidirectional command support

At the block level bidi request uses req->next_rq pointer for a second
bidi_read request.
At Scsi-midlayer a second scsi_data_buffer structure is used for the
bidi_read part. This bidi scsi_data_buffer is put on
request->next_rq->special. Struct scsi_cmnd is not changed.

- Define scsi_bidi_cmnd() to return true if it is a bidi request and a
  second sgtable was allocated.

- Define scsi_in()/scsi_out() to return the in or out scsi_data_buffer
  from this command This API is to isolate users from the mechanics of
  bidi.

- Define scsi_end_bidi_request() to do what scsi_end_request() does but
  for a bidi request. This is necessary because bidi commands are a bit
  tricky here. (See comments in body)

- scsi_release_buffers() will also release the bidi_read scsi_data_buffer

- scsi_io_completion() on bidi commands will now call
  scsi_end_bidi_request() and return.

- The previous work done in scsi_init_io() is now done in a new
  scsi_init_sgtable() (which is 99% identical to old scsi_init_io())
  The new scsi_init_io() will call the above twice if needed also for
  the bidi_read command. Only at this point is a command bidi.

- In scsi_error.c at scsi_eh_prep/restore_cmnd() make sure bidi-lld is not
  confused by a get-sense command that looks like bidi. This is done
  by puting NULL at request->next_rq, and restoring.

[jejb: update to sg_table and resolve conflicts
also update to blk-end-request and resolve conflicts]

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 91 insertions, 15 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index d5e77e9b3a9..681ed1b830f 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -64,6 +64,8 @@ static struct scsi_host_sg_pool scsi_sg_pools[] = {
 };
 #undef SP
 
+static struct kmem_cache *scsi_bidi_sdb_cache;
+
 static void scsi_run_queue(struct request_queue *q);
 
 /*
@@ -790,10 +792,38 @@ void scsi_release_buffers(struct scsi_cmnd *cmd)
                 scsi_free_sgtable(&cmd->sdb);
 
         memset(&cmd->sdb, 0, sizeof(cmd->sdb));
+
+        if (scsi_bidi_cmnd(cmd)) {
+                struct scsi_data_buffer *bidi_sdb =
+                        cmd->request->next_rq->special;
+                scsi_free_sgtable(bidi_sdb);
+                kmem_cache_free(scsi_bidi_sdb_cache, bidi_sdb);
+                cmd->request->next_rq->special = NULL;
+        }
 }
 EXPORT_SYMBOL(scsi_release_buffers);
 
 /*
+ * Bidi commands Must be complete as a whole, both sides at once.
+ * If part of the bytes were written and lld returned
+ * scsi_in()->resid and/or scsi_out()->resid this information will be left
+ * in req->data_len and req->next_rq->data_len. The upper-layer driver can
+ * decide what to do with this information.
+ */
+void scsi_end_bidi_request(struct scsi_cmnd *cmd)
+{
+        blk_end_bidi_request(cmd->request, 0, scsi_out(cmd)->resid,
+                                                        scsi_in(cmd)->resid);
+        scsi_release_buffers(cmd);
+
+        /*
+         * This will goose the queue request function at the end, so we don't
+         * need to worry about launching another command.
+         */
+        scsi_next_command(cmd);
+}
+
+/*
  * Function:    scsi_io_completion()
  *
  * Purpose:     Completion processing for block device I/O requests.
@@ -854,9 +884,15 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
                                 req->sense_len = len;
                         }
                 }
+                if (scsi_bidi_cmnd(cmd)) {
+                        /* will also release_buffers */
+                        scsi_end_bidi_request(cmd);
+                        return;
+                }
                 req->data_len = scsi_get_resid(cmd);
         }
 
+        BUG_ON(blk_bidi_rq(req)); /* bidi not support for !blk_pc_request yet */
         scsi_release_buffers(cmd);
 
         /*
@@ -982,28 +1018,16 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
         scsi_end_request(cmd, -EIO, this_count, !result);
 }
 
-/*
- * Function:    scsi_init_io()
- *
- * Purpose:     SCSI I/O initialize function.
- *
- * Arguments:   cmd   - Command descriptor we wish to initialize
- *
- * Returns:     0 on success
- *              BLKPREP_DEFER if the failure is retryable
- */
-int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
+static int scsi_init_sgtable(struct request *req, struct scsi_data_buffer *sdb,
+                             gfp_t gfp_mask)
 {
-        struct request     *req = cmd->request;
-        int                count;
-        struct scsi_data_buffer *sdb = &cmd->sdb;
+        int count;
 
         /*
          * If sg table allocation fails, requeue request later.
          */
         if (unlikely(scsi_alloc_sgtable(sdb, req->nr_phys_segments,
                                         gfp_mask))) {
-                scsi_unprep_request(req);
                 return BLKPREP_DEFER;
         }
 
@@ -1022,6 +1046,50 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
         sdb->table.nents = count;
         return BLKPREP_OK;
 }
+
+/*
+ * Function:    scsi_init_io()
+ *
+ * Purpose:     SCSI I/O initialize function.
+ *
+ * Arguments:   cmd   - Command descriptor we wish to initialize
+ *
+ * Returns:     0 on success
+ *              BLKPREP_DEFER if the failure is retryable
+ *              BLKPREP_KILL if the failure is fatal
+ */
+int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
+{
+        int error = scsi_init_sgtable(cmd->request, &cmd->sdb, gfp_mask);
+        if (error)
+                goto err_exit;
+
+        if (blk_bidi_rq(cmd->request)) {
+                struct scsi_data_buffer *bidi_sdb = kmem_cache_zalloc(
+                        scsi_bidi_sdb_cache, GFP_ATOMIC);
+                if (!bidi_sdb) {
+                        error = BLKPREP_DEFER;
+                        goto err_exit;
+                }
+
+                cmd->request->next_rq->special = bidi_sdb;
+                error = scsi_init_sgtable(cmd->request->next_rq, bidi_sdb,
+                                                                    GFP_ATOMIC);
+                if (error)
+                        goto err_exit;
+        }
+
+        return BLKPREP_OK ;
+
+err_exit:
+        scsi_release_buffers(cmd);
+        if (error == BLKPREP_KILL)
+                scsi_put_command(cmd);
+        else /* BLKPREP_DEFER */
+                scsi_unprep_request(cmd->request);
+
+        return error;
+}
 EXPORT_SYMBOL(scsi_init_io);
 
 static struct scsi_cmnd *scsi_get_cmd_from_req(struct scsi_device *sdev,
@@ -1639,6 +1707,14 @@ int __init scsi_init_queue(void)
                 return -ENOMEM;
         }
 
+        scsi_bidi_sdb_cache = kmem_cache_create("scsi_bidi_sdb",
+                                        sizeof(struct scsi_data_buffer),
+                                        0, 0, NULL);
+        if (!scsi_bidi_sdb_cache) {
+                printk(KERN_ERR "SCSI: can't init scsi bidi sdb cache\n");
+                return -ENOMEM;
+        }
+
         for (i = 0; i < SG_MEMPOOL_NR; i++) {
                 struct scsi_host_sg_pool *sgp = scsi_sg_pools + i;
                 int size = sgp->size * sizeof(struct scatterlist);