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Bottomley" , "Martin K. Petersen" Cc: linux-scsi@vger.kernel.org, Damien Le Moal , John Garry , Niklas Cassel Subject: [PATCH v4 05/10] scsi: scsi_debug: Report the residual of a write Date: Fri, 18 Sep 2026 08:29:16 +0200 Message-ID: <20260918062910.1709791-17-cassel@kernel.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260918062910.1709791-12-cassel@kernel.org> References: <20260918062910.1709791-12-cassel@kernel.org> Precedence: bulk X-Mailing-List: linux-scsi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4049; i=cassel@kernel.org; h=from:subject; bh=DO/ijweBuDVvHl0rRNw0MsftkaQk8zEsKsLBgwvRCqs=; b=owGbwMvMwCV2MsVw8cxjvkWMp9WSGLLW3LK/aR2+SEeL96vhIab1ZQevnCm+ncccuypTz7rg7 YknxfPOdpSyMIhxMciKKbL4/nDZX9ztPuW44h0bmDmsTCBDGLg4BWAia90Z/ped1vBifdn125Y3 efWs5Dumj75smM50Y13nrKY7vCcWV61m+J+nlPviaO7rydZRAcdXz7d269/MwvzDMlf9kcNqv+7 2u3wA X-Developer-Key: i=cassel@kernel.org; a=openpgp; fpr=5ADE635C0E631CBBD5BE065A352FE6582ED9B5DA Content-Transfer-Encoding: 8bit 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. It also needs a guard that the other two do not. sg_off counts what the command asked for rather than what was transferred: lbdof is not validated against the length of the buffer, and a range is counted in full even when do_device_access() copied less of it, so sg_off can exceed the buffer. The other two subtract the number of bytes that were copied, which the buffer bounds. Assisted-by: LLM Reviewed-by: Damien Le Moal Signed-off-by: Niklas Cassel --- 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 | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c index c68dba6dbbdd..170d5c944b61 100644 --- a/drivers/scsi/scsi_debug.c +++ b/drivers/scsi/scsi_debug.c @@ -5166,6 +5166,8 @@ 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) { @@ -5354,6 +5356,13 @@ 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); @@ -6210,6 +6219,8 @@ 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