[PATCH v8 05/11] scsi: scsi_debug: Report the residual of a write

[Niklas Cassel <cassel@kernel.org>]

A write whose data buffer is larger than its transfer length leaves a
residual that the initiator is entitled to be told about. resp_read_dt0()
and resp_write_tape() report it, but the write paths for a disk do not,
so such a write completes with GOOD status and a residual of zero while
a READ of the same length into the same buffer reports it correctly.

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

resp_write_scat() differs twice over. Its data-out buffer also holds the
parameter list header and the LBA range descriptors, so what the command
consumed is sg_off rather than the bytes that the last range
transferred; and sg_off counts what was asked for rather than what was
transferred, so it can exceed the buffer and needs a guard. Two of its
exits also bypass the end of the loop: a command with no LBA range
descriptors or a buffer transfer length of zero transfers nothing, so
the whole buffer is residual, and an injected error ends the command
after a range has been written, where resp_write_dt0() reports the
residual before injecting it.

Assisted-by: LLM
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
Tested with:

  modprobe scsi_debug zbc=managed sector_size=512 physblk_exp=3 \
      zone_size_mb=8 dev_size_mb=128 zone_nr_conv=2

An eight logical block WRITE(16) with a 5000 byte buffer reports
resid=904, having transferred 4096. A READ(16) of the same length into
the same buffer reported that before this patch and the WRITE reported
0. A buffer of exactly 4096 bytes reports 0, as does a 512 byte buffer,
which is consumed in its entirety. WRITE ATOMIC (16) behaves like the
WRITE, on a device that is not zoned.

WRITE SCATTERED (16) with one LBA range descriptor of eight blocks and a
5632 byte buffer reports resid=1024, having consumed 512 bytes of
parameter list and 4096 bytes of data. The same command with a 1024 byte
buffer completes and reports resid=0: sg_off reaches 4608, past the end
of the buffer, and without the guard the residual would have been
reported as 4294963712.
---
 drivers/scsi/scsi_debug.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index b64ae3ad300d..9220758bb801 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -5162,6 +5162,8 @@ 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) {
@@ -5233,8 +5235,10 @@ static int resp_write_scat(struct scsi_cmnd *scp,
 					    "Unprotected WR to DIF device\n");
 		}
 	}
-	if ((num_lrd == 0) || (bt_len == 0))
+	if (num_lrd == 0 || bt_len == 0) {
+		scsi_set_resid(scp, scsi_bufflen(scp));
 		return 0;       /* T10 says these do-nothings are not errors */
+	}
 	if (lbdof == 0) {
 		if (sdebug_verbose)
 			sdev_printk(KERN_INFO, scp->device,
@@ -5327,6 +5331,9 @@ static int resp_write_scat(struct scsi_cmnd *scp,
 
 		if (unlikely((sdebug_opts & SDEBUG_OPT_RECOV_DIF_DIX) &&
 			     atomic_read(&sdeb_inject_pending))) {
+			if (scsi_bufflen(scp) > sg_off + num_by)
+				scsi_set_resid(scp, scsi_bufflen(scp) -
+					       (sg_off + num_by));
 			if (sdebug_opts & SDEBUG_OPT_RECOVERED_ERR) {
 				mk_sense_buffer(scp, RECOVERED_ERROR,
 					FAILURE_PREDICTION_THRESHOLD_EXCEEDED);
@@ -5350,6 +5357,13 @@ static int resp_write_scat(struct scsi_cmnd *scp,
 		sg_off += num_by;
 		cum_lb += num;
 	}
+	/*
+	 * sg_off counts what the command asked for, which can exceed the
+	 * buffer: lbdof is not validated against it, and a range is counted
+	 * in full even if do_device_access() copied less.
+	 */
+	if (scsi_bufflen(scp) > sg_off)
+		scsi_set_resid(scp, scsi_bufflen(scp) - sg_off);
 	ret = 0;
 err_out_unlock:
 	sdeb_meta_write_unlock(sip);
@@ -6206,6 +6220,8 @@ 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