Patch: lpfc: Modify Emulex lpfc LPFC_DEFAULT_SG_SEG_CNT to 128 for default larger sg_io capability

We have been seeing issues with qemu_kvm virtual guests where if they issue I/O to direct attached SCSI passthrough LUNS with large I/O sizes such as 512K the sg_io will fail with -EINVAL.

Simple reproducer is here.

strace -e ioctl sg_dd if=/dev/zero of=/dev/sdae bpt=0x400 count=0x400 blk_sgio=1
Assume default 'bs' (block size) of 512 bytes
ioctl(4, SG_IO, {'S', SG_DXFER_FROM_DEV, cmd[6]=[12, 00, 00, 00, 24, 00], mx_sb_len=64, iovec_count=0, dxfer_len=36, timeout=60000, flags=0, data[36]=["\0\0\5\2\37\270\0\2LIO-ORG block-15 "...], status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=0, info=0}) = 0
ioctl(4, SG_IO, {'S', SG_DXFER_TO_DEV, cmd[10]=[2a, 00, 00, 00, 00, 00, 00, 04, 00, 00], mx_sb_len=64, iovec_count=0, dxfer_len=524288, timeout=60000, flags=0, data[524288]=["\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...]}) = -1 EINVAL (Invalid argument) writing (SG_IO) on sg device, error: Invalid argument
sg_write failed, seek=0
Some error occurred, remaining block count=1024
1024+0 records in
0+0 records out

Qlogic defaults to 128 so has not been seeing this but lpfc does not. Would like to avoid having to set this in the module parameters to 128.

From: Laurence Oberman <[email protected]>
Date: Wed, 8 Feb 2017 14:49:05 -0500
Subject: [PATCH] Modified LPFC_DEFAULT_SG_SEG_CNT to 128 to match Qlogic. This
will allow larger sg_io passthrough for qemu_kvm guests that expect the larger setting for I/O large rthen 512k.

---
 drivers/scsi/lpfc/lpfc.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 8a20b4e..8f86d41 100644
@@ -42,7 +42,7 @@
 #define LPFC_MAX_NS_RETRY	3	/* Number of retry attempts to contact
 					   the NameServer  before giving up. */
 #define LPFC_CMD_PER_LUN	3	/* max outstanding cmds per lun */
-#define LPFC_DEFAULT_SG_SEG_CNT 64	/* sg element count per scsi cmnd */
+#define LPFC_DEFAULT_SG_SEG_CNT 128	/* sg element count per scsi cmnd */
 #define LPFC_DEFAULT_MENLO_SG_SEG_CNT 128	/* sg element count per scsi
 		cmnd for menlo needs nearly twice as for firmware
 		downloads using bsg */

1.8.3.1

----- Original Message -----

Replying to my own email

I was wondering if we could set it to 256 as the default. This seems to pass sg_io all the way to 0x800

bpt=0x200
Assume default 'bs' (block size) of 512 bytes
ioctl(4, SG_IO, {'S', SG_DXFER_FROM_DEV, cmd[6]=[12, 00, 00, 00, 24, 00], mx_sb_len=64, iovec_count=0, dxfer_len=36, timeout=60000, flags=0, data[36]=["\0\0\5\2\37\270\0\2LIO-ORG block-21 "...], status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=0, info=0}) = 0
ioctl(4, SG_IO, {'S', SG_DXFER_TO_DEV, cmd[10]=[2a, 00, 00, 00, 00, 00, 00, 02, 00, 00], mx_sb_len=64, iovec_count=0, dxfer_len=262144, timeout=60000, flags=0, data[262144]=["\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...], status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=30, info=0}) = 0 512+0 records in
512+0 records out
+++ exited with 0 +++

bpt=0x400
Assume default 'bs' (block size) of 512 bytes
ioctl(4, SG_IO, {'S', SG_DXFER_FROM_DEV, cmd[6]=[12, 00, 00, 00, 24, 00], mx_sb_len=64, iovec_count=0, dxfer_len=36, timeout=60000, flags=0, data[36]=["\0\0\5\2\37\270\0\2LIO-ORG block-21 "...], status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=0, info=0}) = 0
ioctl(4, SG_IO, {'S', SG_DXFER_TO_DEV, cmd[10]=[2a, 00, 00, 00, 00, 00, 00, 04, 00, 00], mx_sb_len=64, iovec_count=0, dxfer_len=524288, timeout=60000, flags=0, data[524288]=["\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...], status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=43, info=0}) = 0 1024+0 records in
1024+0 records out
+++ exited with 0 +++

bpt=0x800
Assume default 'bs' (block size) of 512 bytes
ioctl(4, SG_IO, {'S', SG_DXFER_FROM_DEV, cmd[6]=[12, 00, 00, 00, 24, 00], mx_sb_len=64, iovec_count=0, dxfer_len=36, timeout=60000, flags=0, data[36]=["\0\0\5\2\37\270\0\2LIO-ORG block-21 "...], status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=0, info=0}) = 0
ioctl(4, SG_IO, {'S', SG_DXFER_TO_DEV, cmd[10]=[2a, 00, 00, 00, 00, 00, 00, 08, 00, 00], mx_sb_len=64, iovec_count=0, dxfer_len=1048576, timeout=60000, flags=0, data[1048576]=["\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...], status=00, masked_status=00, sb[0]=[], host_status=0, driver_status=0, resid=0, duration=34, info=0}) = 0 2048+0 records in
2048+0 records out
+++ exited with 0 +++

Thanks
Laurence