Linux Virtualization - Jun 2020 - [PATCH AUTOSEL 5.4 059/266] scsi: vhost: Notify TCM about the maximum sg entries supported per command

From: Sudhakar Panneerselvam <sudhakar.panneerselvam at oracle.com>

[ Upstream commit 5ae6a6a915033bfee79e76e0c374d4f927909edc ]

vhost-scsi pre-allocates the maximum sg entries per command and if a
command requires more than VHOST_SCSI_PREALLOC_SGLS entries, then that
command is failed by it. This patch lets vhost communicate the max sg limit
when it registers vhost_scsi_ops with TCM. With this change, TCM would
report the max sg entries through "Block Limits" VPD page which will
be
typically queried by the SCSI initiator during device discovery. By knowing
this limit, the initiator could ensure the maximum transfer length is less
than or equal to what is reported by vhost-scsi.

Link:
https://lore.kernel.org/r/1590166317-953-1-git-send-email-sudhakar.panneerselvam
at oracle.com
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Jason Wang <jasowang at redhat.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Stefan Hajnoczi <stefanha at redhat.com>
Reviewed-by: Mike Christie <mchristi at redhat.com>
Signed-off-by: Sudhakar Panneerselvam <sudhakar.panneerselvam at
oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen at oracle.com>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/vhost/scsi.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index a9caf1bc3c3e..88ce114790d7 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -2290,6 +2290,7 @@ static struct configfs_attribute *vhost_scsi_wwn_attrs[] =
{
 static const struct target_core_fabric_ops vhost_scsi_ops = {
 	.module				= THIS_MODULE,
 	.fabric_name			= "vhost",
+	.max_data_sg_nents		= VHOST_SCSI_PREALLOC_SGLS,
 	.tpg_get_wwn			= vhost_scsi_get_fabric_wwn,
 	.tpg_get_tag			= vhost_scsi_get_tpgt,
 	.tpg_check_demo_mode		= vhost_scsi_check_true,
-- 
2.25.1