ide-atapi,tape,floppy: allow ->pc_callback() to change rq->data_len

Impact: allow residual count implementation in ->pc_callback()

rq->data_len has two duties - carrying the number of input bytes on
issue and carrying residual count back to the issuer on completion.
ide-atapi completion callback ->pc_callback() is the right place to do
this but currently ide-atapi depends on rq->data_len carrying the
original request size after calling ->pc_callback() to complete the pc
request.

This patch makes ide_pc_intr(), ide_tape_issue_pc() and
ide_floppy_issue_pc() cache length to complete before calling
->pc_callback() so that it can modify rq->data_len as necessary.

Note: As using rq->data_len for two purposes can make cases like this
      incorrect in subtle ways, future changes will introduce separate
      field for residual count.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 10 insertions, 6 deletions

diff --git a/drivers/ide/ide-atapi.c b/drivers/ide/ide-atapi.c
index 5cefe12f5622..3df5442de710 100644
--- a/drivers/ide/ide-atapi.c
+++ b/drivers/ide/ide-atapi.c
@@ -409,6 +409,16 @@ static ide_startstop_t ide_pc_intr(ide_drive_t *drive)
                 if ((pc->flags & PC_FLAG_WAIT_FOR_DSC) && (stat & ATA_DSC) == 0)
                         dsc = 1;
 
+                /*
+                 * ->pc_callback() might change rq->data_len for
+                 * residual count, cache total length.
+                 */
+                if (!blk_special_request(rq) &&
+                    (drive->media == ide_tape && !rq->bio))
+                        done = ide_rq_bytes(rq);        /* FIXME */
+                else
+                        done = blk_rq_bytes(rq);
+
                 /* Command finished - Call the callback function */
                 uptodate = drive->pc_callback(drive, dsc);
 
@@ -417,7 +427,6 @@ static ide_startstop_t ide_pc_intr(ide_drive_t *drive)
 
                 if (blk_special_request(rq)) {
                         rq->errors = 0;
-                        done = blk_rq_bytes(rq);
                         error = 0;
                 } else {
 
@@ -426,11 +435,6 @@ static ide_startstop_t ide_pc_intr(ide_drive_t *drive)
                                         rq->errors = -EIO;
                         }
 
-                        if (drive->media == ide_tape && !rq->bio)
-                                done = ide_rq_bytes(rq); /* FIXME */
-                        else
-                                done = blk_rq_bytes(rq);
-
                         error = uptodate ? 0 : -EIO;
                 }