[SCSI] add use_sg_chaining option to scsi_host_template

This option is true if a low-level driver can support sg
chaining. This will be removed eventually when all the drivers are
converted to support sg chaining. q->max_phys_segments is set to
SCSI_MAX_SG_SEGMENTS if false.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 7d210cd6c38d..0fd4746ee39d 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -39,6 +39,9 @@ struct blk_queue_tags;
 #define DISABLE_CLUSTERING 0
 #define ENABLE_CLUSTERING 1
 
+#define DISABLE_SG_CHAINING 0
+#define ENABLE_SG_CHAINING 1
+
 enum scsi_eh_timer_return {
         EH_NOT_HANDLED,
         EH_HANDLED,
@@ -443,6 +446,15 @@ struct scsi_host_template {
         unsigned ordered_tag:1;
 
         /*
+         * true if the low-level driver can support sg chaining. this
+         * will be removed eventually when all the drivers are
+         * converted to support sg chaining.
+         *
+         * Status: OBSOLETE
+         */
+        unsigned use_sg_chaining:1;
+
+        /*
          * Countdown for host blocking with no commands outstanding
          */
         unsigned int max_host_blocked;
@@ -586,6 +598,7 @@ struct Scsi_Host {
         unsigned unchecked_isa_dma:1;
         unsigned use_clustering:1;
         unsigned use_blk_tcq:1;
+        unsigned use_sg_chaining:1;
 
         /*
          * Host has requested that no further requests come through for the