sd: add missing scenario for sd_config_write_same

From: Tom Yan <[email protected]>

Example:

[root@localhost ~]# sg_opcodes /dev/sdb > /dev/null Report supported operation codes: Illegal request, invalid opcode

[root@localhost ~]# sg_vpd -p bl /dev/sdb | grep 'write same'
Maximum write same length: 0x0 blocks

[root@localhost ~]# cat /sys/block/sdb/queue/write_same_max_bytes 33553920

index d749da7..1179ec1 100644
@@ -807,6 +807,8 @@ static void sd_config_write_same(struct scsi_disk *sdkp)
 	if (sdkp->max_ws_blocks > SD_MAX_WS10_BLOCKS)
 		sdkp->max_ws_blocks = min_not_zero(sdkp->max_ws_blocks,
 						   (u32)SD_MAX_WS16_BLOCKS);
+	else if (sdkp->max_ws_blocks == 0 && sdkp->device->no_report_opcodes)
+		sdkp->device->no_write_same = 1;
 	else if (sdkp->ws16 || sdkp->ws10 || sdkp->device->no_report_opcodes)
 		sdkp->max_ws_blocks = min_not_zero(sdkp->max_ws_blocks,
 						   (u32)SD_MAX_WS10_BLOCKS);

2.7.1

Tom,

tom> [root@localhost ~]# sg_opcodes /dev/sdb > /dev/null Report tom> supported operation codes: Illegal request, invalid opcode

tom> [root@localhost ~]# sg_vpd -p bl /dev/sdb | grep 'write same' tom> Maximum write same length: 0x0 blocks

"A MAXIMUM WRITE SAME LENGTH field set to zero indicates that the device server does not report a limit on the number of logical blocks that it allows to be unmapped or written in a single WRITE SAME command."

I.e. that parameter says nothing about whether WRITE SAME is supported or not.

tom> [root@localhost ~]# cat /sys/block/sdb/queue/write_same_max_bytes tom> 33553920

That's correct behavior. Unless otherwise noted we default to issuing 32 MB WRITE SAME commands and will subsequently turn it off if the drive returns a failure.

WRITE SAME support on storage devices predates RSOC, most of the common VPD pages, etc. So there is no reliable value we can key off of to determine whether a drive supports the command. And because a block count of 0 is interpreted as "the entire device" we can't issue a non-destructive WRITE SAME to determine whether device supports it or not. Consequently we are stuck with assuming it works unless RSOC is supported or the device sits behind a SATL.

Do you have a particular drive that is causing problems? We could quirk it or add additional heuristics in addition to the ATA Information VPD.

Martin K. Petersen	Oracle Linux Engineering

Fair enough.

Nah so far the device never showed any problems. It's actually a SATA/USB adapter with UAS support. In fact it is seemingly coherent to the heuristics:

[tom@localhost ~]$ sudo sg_vpd /dev/sdb
Supported VPD pages VPD page:
Supported VPD pages [sv]
Unit serial number [sn]
Device identification [di]
Block limits (SBC) [bl]

[tom@localhost ~]$ sudo sg_vpd -p bl /dev/sdb Block limits VPD page (SBC):
Write same non-zero (WSNZ): 0
Maximum compare and write length: 0 blocks Optimal transfer length granularity: 1 blocks Maximum transfer length: 65535 blocks
Optimal transfer length: 65535 blocks
Maximum prefetch length: 65535 blocks
Maximum unmap LBA count: 0
Maximum unmap block descriptor count: 0 Optimal unmap granularity: 0
Unmap granularity alignment valid: 0
Unmap granularity alignment: 0
Maximum write same length: 0x0 blocks
Maximum atomic transfer length: 0
Atomic alignment: 0
Atomic transfer length granularity: 0
Maximum atomic transfer length with atomic boundary: 0 Maximum atomic boundary size: 0

Since you've mentioned it, why do we disable write same for all devices with a ATA Information VPD?

Tom> Since you've mentioned it, why do we disable write same for all Tom> devices with a ATA Information VPD?

Generally speaking, SAS controllers that properly translate SCSI WRITE SAME to ATA ditto also support modern features such as the REPORT SUPPORTED OPERATION CODES command.

For the SAS controllers that do not support RSOC we check for the ATA Information VPD page to determine whether we are talking to a SAS or SATA device. If it's a SATA device we skip WRITE SAME because in most cases either the controller's SATL or the drive itself will fail miserably.

Martin K. Petersen	Oracle Linux Engineering