target: Untangle front-end and back-end meanings of max_sectors attribute

se_dev_attrib.max_sectors currently has two independent meanings:

 - It is reported in the block limits VPD page as the maximum transfer
   length, ie the largest IO that the front-end (fabric) can handle.
   Also the target core doesn't enforce this maximum transfer length.

 - It is used to hold the size of the largest IO that the back-end can
   handle, so we know when to split SCSI commands into multiple tasks.

Fix this by adding a new se_dev_attrib.fabric_max_sectors to hold the
maximum transfer length, and checking incoming IOs against that limit.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 99d7373..1641dea 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -86,6 +86,8 @@
 #define DA_UNMAP_GRANULARITY_DEFAULT		0
 /* Default unmap_granularity_alignment */
 #define DA_UNMAP_GRANULARITY_ALIGNMENT_DEFAULT	0
+/* Default max transfer length */
+#define DA_FABRIC_MAX_SECTORS			8192
 /* Emulation for Direct Page Out */
 #define DA_EMULATE_DPO				0
 /* Emulation for Forced Unit Access WRITEs */
@@ -726,6 +728,7 @@ struct se_dev_attrib {
 	u32		block_size;
 	u32		hw_max_sectors;
 	u32		max_sectors;
+	u32		fabric_max_sectors;
 	u32		optimal_sectors;
 	u32		hw_queue_depth;
 	u32		queue_depth;