On 2020-10-30 5:39 p.m., David Disseldorp wrote:
SBC-4 r15 5.3 COMPARE AND WRITE command states:
if the compare operation does not indicate a match, then terminate the
command with CHECK CONDITION status with the sense key set to
MISCOMPARE and the additional sense code set to MISCOMPARE DURING
VERIFY OPERATION. In the sense data (see 4.18 and SPC-5) the offset
from the start of the Data-Out Buffer to the first byte of data that
was not equal shall be reported in the INFORMATION field.
This change implements the missing logic to report the miscompare offset
in the sense data INFORMATION field.
Signed-off-by: David Disseldorp <ddiss@xxxxxxx>
Reviewed-by: Mike Christie <michael.christie@xxxxxxxxxx>
---
drivers/target/target_core_sbc.c | 34 ++++++++++++++++++--------
drivers/target/target_core_transport.c | 1 +
2 files changed, 25 insertions(+), 10 deletions(-)
diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
index 22d0cbba6ff3..0fa52a98d6cf 100644
--- a/drivers/target/target_core_sbc.c
+++ b/drivers/target/target_core_sbc.c
@@ -435,13 +435,13 @@ static sense_reason_t compare_and_write_post(struct se_cmd *cmd, bool success,
}
/*
- * compare @cmp_len bytes of @read_sgl with @cmp_sgl. On miscompare return
- * TCM_MISCOMPARE_VERIFY.
+ * compare @cmp_len bytes of @read_sgl with @cmp_sgl. On miscompare, fill
+ * @miscmp_off and return TCM_MISCOMPARE_VERIFY.
*/
static sense_reason_t
compare_and_write_do_cmp(struct scatterlist *read_sgl, unsigned int read_nents,
struct scatterlist *cmp_sgl, unsigned int cmp_nents,
- unsigned int cmp_len)
+ unsigned int cmp_len, unsigned int *miscmp_off)
{
unsigned char *buf = NULL;
struct scatterlist *sg;
@@ -467,17 +467,20 @@ compare_and_write_do_cmp(struct scatterlist *read_sgl, unsigned int read_nents,
*/
offset = 0;
for_each_sg(read_sgl, sg, read_nents, i) {
+ unsigned int i;
unsigned int len = min(sg->length, cmp_len);
unsigned char *addr = kmap_atomic(sg_page(sg));
- if (memcmp(addr, buf + offset, len)) {
- pr_warn("Detected MISCOMPARE for addr: %p buf: %p\n",
- addr, buf + offset);
- kunmap_atomic(addr);
+ for (i = 0; i < len && addr[i] == buf[offset + i]; i++)
+ ;
I believe the logic is correct (and scsi_debug doesn't set the INFO field
in its CAW, but should), but I wonder about performance.
If the probability of equality is high (e.g. like it is usually with
VERIFY(BytChk=1) ) and memcmp() is faster than that for-loop (which
could be optimized), then a better strategy might be to always do memcmp()
first and only if it fails go into the byte by byte for-loop to find the
offset of the first miscompare.
IMO this should only be considered, if there is going to be a "v4" of
this patchset.
Doug Gilbert
+ kunmap_atomic(addr);
+ if (i < len) {
+ *miscmp_off = offset + i;
+ pr_warn("Detected MISCOMPARE at offset %u\n",
+ *miscmp_off);
ret = TCM_MISCOMPARE_VERIFY;
goto out;
}
- kunmap_atomic(addr);
offset += len;
cmp_len -= len;
@@ -501,6 +504,7 @@ static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool succes
unsigned int len;
unsigned int block_size = dev->dev_attrib.block_size;
unsigned int compare_len = (cmd->t_task_nolb * block_size);
+ unsigned int miscmp_off = 0;
sense_reason_t ret = TCM_NO_SENSE;
int i;
@@ -532,8 +536,18 @@ static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool succes
cmd->t_bidi_data_nents,
cmd->t_data_sg,
cmd->t_data_nents,
- compare_len);
- if (ret)
+ compare_len,
+ &miscmp_off);
+ if (ret == TCM_MISCOMPARE_VERIFY) {
+ /*
+ * SBC-4 r15: 5.3 COMPARE AND WRITE command
+ * In the sense data (see 4.18 and SPC-5) the offset from the
+ * start of the Data-Out Buffer to the first byte of data that
+ * was not equal shall be reported in the INFORMATION field.
+ */
+ cmd->sense_info = miscmp_off;
+ goto out;
+ } else if (ret)
goto out;
if (sg_alloc_table(&write_tbl, cmd->t_data_nents, GFP_KERNEL) < 0) {
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index c6f45c12d564..693ed3fe4388 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -3196,6 +3196,7 @@ static const struct sense_detail sense_detail_table[] = {
.key = MISCOMPARE,
.asc = 0x1d, /* MISCOMPARE DURING VERIFY OPERATION */
.ascq = 0x00,
+ .add_sense_info = true,
},
[TCM_LOGICAL_BLOCK_GUARD_CHECK_FAILED] = {
.key = ABORTED_COMMAND,
