[PATCH v3 1/6] scsi: scsi_debug: Report the residual of a write

[Niklas Cassel <cassel@kernel.org>]

A command transfers the number of logical blocks that it asks for,
bounded by the data buffer that the initiator provided. When the buffer
is larger than that, the bytes beyond are not transferred, and the
difference is a residual that the initiator is entitled to be told
about.

resp_read_dt0() reports it, as does resp_write_tape(), but the write
paths for a disk do not: scsi_get_resid() keeps the zero that
scsi_debug_queuecommand() initialised it with, so a write with an
oversized buffer completes with GOOD status and a residual of zero, as
though the whole buffer had been consumed. A READ of the same length
into the same buffer reports the residual correctly, so the two
directions disagree.

Report it in resp_write_dt0(), resp_write_scat() and
resp_atomic_write().

resp_write_scat() needs a different expression from the other two. Its
data-out buffer holds the parameter list header and the LBA range
descriptors as well as the data, and sg_off walks over all of it, from
the offset at which the data begins to the end of the last range that
was written, so what the command consumed is sg_off and not the number
of bytes that the last range transferred.

Assisted-by: LLM
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 drivers/scsi/scsi_debug.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 6941809dfdb7..641dd6f93791 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -5164,6 +5164,8 @@ static int resp_write_dt0(struct scsi_cmnd *scp, struct sdebug_dev_info *devip)
 			    "%s: write: cdb indicated=%u, IO sent=%d bytes\n",
 			    my_name, num * sdebug_sector_size, ret);
 
+	scsi_set_resid(scp, scsi_bufflen(scp) - ret);
+
 	if (unlikely((sdebug_opts & SDEBUG_OPT_RECOV_DIF_DIX) &&
 		     atomic_read(&sdeb_inject_pending))) {
 		if (sdebug_opts & SDEBUG_OPT_RECOVERED_ERR) {
@@ -5352,6 +5354,7 @@ static int resp_write_scat(struct scsi_cmnd *scp,
 		sg_off += num_by;
 		cum_lb += num;
 	}
+	scsi_set_resid(scp, scsi_bufflen(scp) - sg_off);
 	ret = 0;
 err_out_unlock:
 	sdeb_meta_write_unlock(sip);
@@ -6207,6 +6210,8 @@ static int resp_atomic_write(struct scsi_cmnd *scp,
 		return DID_ERROR << 16;
 	if (unlikely(ret != len * sdebug_sector_size))
 		return DID_ERROR << 16;
+
+	scsi_set_resid(scp, scsi_bufflen(scp) - ret);
 	return 0;
 }
 
-- 
2.55.0