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>

3 files changed, 47 insertions, 11 deletions

diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
index f2aa7543d20a..d10cbed23472 100644
--- a/drivers/target/target_core_device.c
+++ b/drivers/target/target_core_device.c
@@ -772,6 +772,12 @@ int se_dev_set_emulate_write_cache(struct se_device *dev, int flag)
                 pr_err("emulate_write_cache not supported for pSCSI\n");
                 return -EINVAL;
         }
+        if (dev->transport->get_write_cache) {
+                pr_warn("emulate_write_cache cannot be changed when underlying"
+                        " HW reports WriteCacheEnabled, ignoring request\n");
+                return 0;
+        }
+
         dev->dev_attrib.emulate_write_cache = flag;
         pr_debug("dev[%p]: SE Device WRITE_CACHE_EMULATION flag: %d\n",
                         dev, dev->dev_attrib.emulate_write_cache);
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)
diff --git a/drivers/target/target_core_spc.c b/drivers/target/target_core_spc.c
index fa2447004006..803339516fb9 100644
--- a/drivers/target/target_core_spc.c
+++ b/drivers/target/target_core_spc.c
@@ -407,16 +407,31 @@ check_scsi_name:
 }
 EXPORT_SYMBOL(spc_emulate_evpd_83);
 
+static bool
+spc_check_dev_wce(struct se_device *dev)
+{
+        bool wce = false;
+
+        if (dev->transport->get_write_cache)
+                wce = dev->transport->get_write_cache(dev);
+        else if (dev->dev_attrib.emulate_write_cache > 0)
+                wce = true;
+
+        return wce;
+}
+
 /* Extended INQUIRY Data VPD Page */
 static sense_reason_t
 spc_emulate_evpd_86(struct se_cmd *cmd, unsigned char *buf)
 {
+        struct se_device *dev = cmd->se_dev;
+
         buf[3] = 0x3c;
         /* Set HEADSUP, ORDSUP, SIMPSUP */
         buf[5] = 0x07;
 
         /* If WriteCache emulation is enabled, set V_SUP */
-        if (cmd->se_dev->dev_attrib.emulate_write_cache > 0)
+        if (spc_check_dev_wce(dev))
                 buf[6] = 0x01;
         return 0;
 }
@@ -766,7 +781,7 @@ static int spc_modesense_caching(struct se_device *dev, u8 pc, u8 *p)
         if (pc == 1)
                 goto out;
 
-        if (dev->dev_attrib.emulate_write_cache > 0)
+        if (spc_check_dev_wce(dev))
                 p[2] = 0x04; /* Write Cache Enable */
         p[12] = 0x20; /* Disabled Read Ahead */
 
@@ -878,7 +893,7 @@ static sense_reason_t spc_emulate_modesense(struct se_cmd *cmd)
              (cmd->se_deve->lun_flags & TRANSPORT_LUNFLAGS_READ_ONLY)))
                 spc_modesense_write_protect(&buf[length], type);
 
-        if ((dev->dev_attrib.emulate_write_cache > 0) &&
+        if ((spc_check_dev_wce(dev)) &&
             (dev->dev_attrib.emulate_fua_write > 0))
                 spc_modesense_dpofua(&buf[length], type);