[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, 3 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 4f4edc388c07..045a0868fc7b 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -618,9 +618,11 @@ void scsi_eh_prep_cmnd(struct scsi_cmnd *scmd, struct scsi_eh_save *ses,
         memcpy(ses->cmnd, scmd->cmnd, sizeof(scmd->cmnd));
         ses->data_direction = scmd->sc_data_direction;
         ses->sdb = scmd->sdb;
+        ses->next_rq = scmd->request->next_rq;
         ses->result = scmd->result;
 
         memset(&scmd->sdb, 0, sizeof(scmd->sdb));
+        scmd->request->next_rq = NULL;
 
         if (sense_bytes) {
                 scmd->sdb.length = min_t(unsigned, SCSI_SENSE_BUFFERSIZE,
@@ -673,6 +675,7 @@ void scsi_eh_restore_cmnd(struct scsi_cmnd* scmd, struct scsi_eh_save *ses)
         memcpy(scmd->cmnd, ses->cmnd, sizeof(scmd->cmnd));
         scmd->sc_data_direction = ses->data_direction;
         scmd->sdb = ses->sdb;
+        scmd->request->next_rq = ses->next_rq;
         scmd->result = ses->result;
 }
 EXPORT_SYMBOL(scsi_eh_restore_cmnd);