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>

2 files changed, 60 insertions, 4 deletions

diff --git a/drivers/target/target_core_spc.c b/drivers/target/target_core_spc.c
index a07d455e0dd5..0e0456f6a282 100644
--- a/drivers/target/target_core_spc.c
+++ b/drivers/target/target_core_spc.c
@@ -477,8 +477,8 @@ static sense_reason_t
 spc_emulate_evpd_b0(struct se_cmd *cmd, unsigned char *buf)
 {
         struct se_device *dev = cmd->se_dev;
-        int have_tp = 0;
-        int opt, min;
+        u32 mtl = 0;
+        int have_tp = 0, opt, min;
 
         /*
          * Following spc3r22 section 6.5.3 Block Limits VPD page, when
@@ -509,8 +509,15 @@ spc_emulate_evpd_b0(struct se_cmd *cmd, unsigned char *buf)
 
         /*
          * Set MAXIMUM TRANSFER LENGTH
+         *
+         * XXX: Currently assumes single PAGE_SIZE per scatterlist for fabrics
+         * enforcing maximum HW scatter-gather-list entry limit
          */
-        put_unaligned_be32(dev->dev_attrib.hw_max_sectors, &buf[8]);
+        if (cmd->se_tfo->max_data_sg_nents) {
+                mtl = (cmd->se_tfo->max_data_sg_nents * PAGE_SIZE) /
+                       dev->dev_attrib.block_size;
+        }
+        put_unaligned_be32(min_not_zero(mtl, dev->dev_attrib.hw_max_sectors), &buf[8]);
 
         /*
          * Set OPTIMAL TRANSFER LENGTH
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 3f0b50082de4..62bafaa670f4 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -1075,6 +1075,55 @@ transport_set_vpd_ident(struct t10_vpd *vpd, unsigned char *page_83)
 }
 EXPORT_SYMBOL(transport_set_vpd_ident);
 
+static sense_reason_t
+target_check_max_data_sg_nents(struct se_cmd *cmd, struct se_device *dev,
+                               unsigned int size)
+{
+        u32 mtl;
+
+        if (!cmd->se_tfo->max_data_sg_nents)
+                return TCM_NO_SENSE;
+        /*
+         * Check if fabric enforced maximum SGL entries per I/O descriptor
+         * exceeds se_cmd->data_length.  If true, set SCF_UNDERFLOW_BIT +
+         * residual_count and reduce original cmd->data_length to maximum
+         * length based on single PAGE_SIZE entry scatter-lists.
+         */
+        mtl = (cmd->se_tfo->max_data_sg_nents * PAGE_SIZE);
+        if (cmd->data_length > mtl) {
+                /*
+                 * If an existing CDB overflow is present, calculate new residual
+                 * based on CDB size minus fabric maximum transfer length.
+                 *
+                 * If an existing CDB underflow is present, calculate new residual
+                 * based on original cmd->data_length minus fabric maximum transfer
+                 * length.
+                 *
+                 * Otherwise, set the underflow residual based on cmd->data_length
+                 * minus fabric maximum transfer length.
+                 */
+                if (cmd->se_cmd_flags & SCF_OVERFLOW_BIT) {
+                        cmd->residual_count = (size - mtl);
+                } else if (cmd->se_cmd_flags & SCF_UNDERFLOW_BIT) {
+                        u32 orig_dl = size + cmd->residual_count;
+                        cmd->residual_count = (orig_dl - mtl);
+                } else {
+                        cmd->se_cmd_flags |= SCF_UNDERFLOW_BIT;
+                        cmd->residual_count = (cmd->data_length - mtl);
+                }
+                cmd->data_length = mtl;
+                /*
+                 * Reset sbc_check_prot() calculated protection payload
+                 * length based upon the new smaller MTL.
+                 */
+                if (cmd->prot_length) {
+                        u32 sectors = (mtl / dev->dev_attrib.block_size);
+                        cmd->prot_length = dev->prot_length * sectors;
+                }
+        }
+        return TCM_NO_SENSE;
+}
+
 sense_reason_t
 target_cmd_size_check(struct se_cmd *cmd, unsigned int size)
 {
@@ -1120,7 +1169,7 @@ target_cmd_size_check(struct se_cmd *cmd, unsigned int size)
                 }
         }
 
-        return 0;
+        return target_check_max_data_sg_nents(cmd, dev, size);
 
 }