target/iblock: Use backend REQ_FLUSH hint for WriteCacheEnabled status

This patch allows IBLOCK to check block hints in request_queue->flush_flags
when reporting current backend device WriteCacheEnabled status to a remote
SCSI initiator port.

This is done via a se_subsystem_api->get_write_cache() call instead of a
backend se_device creation time flag, as we expect REQ_FLUSH bits to possibly
change from an underlying blk_queue_flush() by the SCSI disk driver, or
internal raw struct block_device driver usage.

Also go ahead and update iblock_execute_rw() bio I/O path code to use
REQ_FLUSH + REQ_FUA hints when determining WRITE_FUA usage, and make SPC
emulation code use a spc_check_dev_wce() helper to handle both types of
cases for virtual backend subsystem drivers.

(asias: Drop unnecessary comparsion operators)

Reported-by: majianpeng <majianpeng@gmail.com>
Cc: majianpeng <majianpeng@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: James Bottomley <JBottomley@Parallels.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 23 insertions, 8 deletions

diff --git a/drivers/target/target_core_iblock.c b/drivers/target/target_core_iblock.c
index b526d23dcd4f..2f74e17ad3e6 100644
--- a/drivers/target/target_core_iblock.c
+++ b/drivers/target/target_core_iblock.c
@@ -154,6 +154,7 @@ static int iblock_configure_device(struct se_device *dev)
 
         if (blk_queue_nonrot(q))
                 dev->dev_attrib.is_nonrot = 1;
+
         return 0;
 
 out_free_bioset:
@@ -654,20 +655,24 @@ iblock_execute_rw(struct se_cmd *cmd)
         u32 sg_num = sgl_nents;
         sector_t block_lba;
         unsigned bio_cnt;
-        int rw;
+        int rw = 0;
         int i;
 
         if (data_direction == DMA_TO_DEVICE) {
+                struct iblock_dev *ib_dev = IBLOCK_DEV(dev);
+                struct request_queue *q = bdev_get_queue(ib_dev->ibd_bd);
                 /*
-                 * Force data to disk if we pretend to not have a volatile
-                 * write cache, or the initiator set the Force Unit Access bit.
+                 * Force writethrough using WRITE_FUA if a volatile write cache
+                 * is not enabled, or if initiator set the Force Unit Access bit.
                  */
-                if (dev->dev_attrib.emulate_write_cache == 0 ||
-                    (dev->dev_attrib.emulate_fua_write > 0 &&
-                     (cmd->se_cmd_flags & SCF_FUA)))
-                        rw = WRITE_FUA;
-                else
+                if (q->flush_flags & REQ_FUA) {
+                        if (cmd->se_cmd_flags & SCF_FUA)
+                                rw = WRITE_FUA;
+                        else if (!(q->flush_flags & REQ_FLUSH))
+                                rw = WRITE_FUA;
+                } else {
                         rw = WRITE;
+                }
         } else {
                 rw = READ;
         }
@@ -774,6 +779,15 @@ iblock_parse_cdb(struct se_cmd *cmd)
         return sbc_parse_cdb(cmd, &iblock_sbc_ops);
 }
 
+bool iblock_get_write_cache(struct se_device *dev)
+{
+        struct iblock_dev *ib_dev = IBLOCK_DEV(dev);
+        struct block_device *bd = ib_dev->ibd_bd;
+        struct request_queue *q = bdev_get_queue(bd);
+
+        return q->flush_flags & REQ_FLUSH;
+}
+
 static struct se_subsystem_api iblock_template = {
         .name                   = "iblock",
         .inquiry_prod           = "IBLOCK",
@@ -790,6 +804,7 @@ static struct se_subsystem_api iblock_template = {
         .show_configfs_dev_params = iblock_show_configfs_dev_params,
         .get_device_type        = sbc_get_device_type,
         .get_blocks             = iblock_get_blocks,
+        .get_write_cache        = iblock_get_write_cache,
 };
 
 static int __init iblock_module_init(void)