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

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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>
This commit is contained in:
Roland Dreier
2012-02-13 16:18:17 -08:00
committed by Nicholas Bellinger
parent effc6cc882
commit 015487b89f
6 changed files with 76 additions and 7 deletions
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include/target/target_core_base.h
+3
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@@ -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;