target/qla2xxx: Honor max_data_sg_nents I/O transfer limit

This patch adds an optional fabric driver provided SGL limit
that target-core will honor as it's own internal I/O maximum
transfer length limit, as exposed by EVPD=0xb0 block limits
parameters.

This is required for handling cases when host I/O transfer
length exceeds the requested EVPD block limits maximum
transfer length. The initial user of this logic is qla2xxx,
so that we can avoid having to reject I/Os from some legacy
FC hosts where EVPD=0xb0 parameters are not honored.

When se_cmd payload length exceeds the provided limit in
target_check_max_data_sg_nents() code, se_cmd->data_length +
se_cmd->prot_length are reset with se_cmd->residual_count
plus underflow bit for outgoing TFO response callbacks.
It also checks for existing CDB level underflow + overflow
and recalculates final residual_count as necessary.

Note this patch currently assumes 1:1 mapping of PAGE_SIZE
per struct scatterlist entry.

Reported-by: Craig Watson <craig.watson@vanguard-rugged.com>
Cc: Craig Watson <craig.watson@vanguard-rugged.com>
Tested-by: Himanshu Madhani <himanshu.madhani@qlogic.com>
Cc: Roland Dreier <roland@purestorage.com>
Cc: Arun Easi <arun.easi@qlogic.com>
Cc: Giridhar Malavali <giridhar.malavali@qlogic.com>
Cc: Andrew Vasquez <andrew.vasquez@qlogic.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/target/target_core_fabric.h b/include/target/target_core_fabric.h
index 69355feabd1d..7fb2557a760e 100644
--- a/include/target/target_core_fabric.h
+++ b/include/target/target_core_fabric.h
@@ -5,6 +5,19 @@ struct target_core_fabric_ops {
 	struct module *module;
 	const char *name;
 	size_t node_acl_size;
+	/*
+	 * Limits number of scatterlist entries per SCF_SCSI_DATA_CDB payload.
+	 * Setting this value tells target-core to enforce this limit, and
+	 * report as INQUIRY EVPD=b0 MAXIMUM TRANSFER LENGTH.
+	 *
+	 * target-core will currently reset se_cmd->data_length to this
+	 * maximum size, and set UNDERFLOW residual count if length exceeds
+	 * this limit.
+	 *
+	 * XXX: Not all initiator hosts honor this block-limit EVPD
+	 * XXX: Currently assumes single PAGE_SIZE per scatterlist entry
+	 */
+	u32 max_data_sg_nents;
 	char *(*get_fabric_name)(void);
 	char *(*tpg_get_wwn)(struct se_portal_group *);
 	u16 (*tpg_get_tag)(struct se_portal_group *);