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 <[email protected]>
Cc: Craig Watson <[email protected]>
Tested-by: Himanshu Madhani <[email protected]>
Cc: Roland Dreier <[email protected]>
Cc: Arun Easi <[email protected]>
Cc: Giridhar Malavali <[email protected]>
Cc: Andrew Vasquez <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Martin K. Petersen <[email protected]>
Signed-off-by: Nicholas Bellinger <[email protected]>

drivers/scsi/qla2xxx/tcm_qla2xxx.c

@@ -1808,6 +1808,11 @@ static const struct target_core_fabric_ops tcm_qla2xxx_ops = {
 	.module				= THIS_MODULE,
 	.name				= "qla2xxx",
 	.node_acl_size			= sizeof(struct tcm_qla2xxx_nacl),
+	/*
+	 * XXX: Limit assumes single page per scatter-gather-list entry.
+	 * Current maximum is ~4.9 MB per se_cmd->t_data_sg with PAGE_SIZE=4096
+	 */
+	.max_data_sg_nents		= 1200,
 	.get_fabric_name		= tcm_qla2xxx_get_fabric_name,
 	.tpg_get_wwn			= tcm_qla2xxx_get_fabric_wwn,
 	.tpg_get_tag			= tcm_qla2xxx_get_tag,