diff mbox series

[v3,4/4] scsi: target: return COMPARE AND WRITE miscompare offsets

Message ID 20201030213931.10720-5-ddiss@suse.de (mailing list archive)
State Superseded
Headers show
Series scsi: target: COMPARE AND WRITE miscompare sense | expand

Commit Message

David Disseldorp Oct. 30, 2020, 9:39 p.m. UTC 
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@suse.de>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
---
 drivers/target/target_core_sbc.c       | 34 ++++++++++++++++++--------
 drivers/target/target_core_transport.c |  1 +
 2 files changed, 25 insertions(+), 10 deletions(-)

Comments

Douglas Gilbert Oct. 31, 2020, 12:06 a.m. UTC | #1 
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@suse.de>
> Reviewed-by: Mike Christie <michael.christie@oracle.com>
> ---
>   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,
>
David Disseldorp Oct. 31, 2020, 10:38 a.m. UTC | #2 
On Fri, 30 Oct 2020 20:06:31 -0400, Douglas Gilbert wrote:

> 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.

While adding the INFO return to tgt I noticed that it had the same
memcmp-with-miscompare-for-loop logic that you describe. I'm only aware
of ESXi as a COMPARE AND WRITE consumer and I think probability of
equality is quite high (@Dirk: perhaps you can confirm?).

> IMO this should only be considered, if there is going to be a "v4" of
> this patchset.

I think this optimization wouldn't make the code much more complex, so
I'll do a re-spin with this change. Thanks for the feedback.

Cheers, David
diff mbox series

Patch

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++)
+			;
+		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,