target: do not reject FUA CDBs when write cache is enabled but emulate_write_cache is 0

A check that rejects a CDB with FUA bit set if no write cache is
emulated was added by the following commit:

  fde9f50f target: Add sanity checks for DPO/FUA bit usage

The condition is as follows:

  if (!dev->dev_attrib.emulate_fua_write ||
      !dev->dev_attrib.emulate_write_cache)

However, this check is wrong if the backend device supports WCE but
"emulate_write_cache" is disabled.

This patch uses se_dev_check_wce() (previously named
spc_check_dev_wce) to invoke transport->get_write_cache() if the
device has a write cache or check the "emulate_write_cache" attribute
otherwise.
Reported-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christophe Vu-Brugier <cvubrugier@fastmail.fm>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_device.c

@@ -650,6 +650,18 @@ static u32 se_dev_align_max_sectors(u32 max_sectors, u32 block_size)
 	return aligned_max_sectors;
 }
 
+bool se_dev_check_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;
+}
+
 int se_dev_set_max_unmap_lba_count(
 	struct se_device *dev,
 	u32 max_unmap_lba_count)

drivers/target/target_core_sbc.c

@@ -708,8 +708,7 @@ sbc_check_dpofua(struct se_device *dev, struct se_cmd *cmd, unsigned char *cdb)
 		}
 	}
 	if (cdb[1] & 0x8) {
-		if (!dev->dev_attrib.emulate_fua_write ||
-		    !dev->dev_attrib.emulate_write_cache) {
+		if (!dev->dev_attrib.emulate_fua_write || !se_dev_check_wce(dev)) {
 			pr_err("Got CDB: 0x%02x with FUA bit set, but device"
 			       " does not advertise support for FUA write\n",
 			       cdb[0]);

drivers/target/target_core_spc.c

@@ -454,19 +454,6 @@ spc_emulate_evpd_83(struct se_cmd *cmd, unsigned char *buf)
 }
 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)
@@ -490,7 +477,7 @@ spc_emulate_evpd_86(struct se_cmd *cmd, unsigned char *buf)
 	buf[5] = 0x07;
 
 	/* If WriteCache emulation is enabled, set V_SUP */
-	if (spc_check_dev_wce(dev))
+	if (se_dev_check_wce(dev))
 		buf[6] = 0x01;
 	/* If an LBA map is present set R_SUP */
 	spin_lock(&cmd->se_dev->t10_alua.lba_map_lock);
@@ -897,7 +884,7 @@ static int spc_modesense_caching(struct se_cmd *cmd, u8 pc, u8 *p)
 	if (pc == 1)
 		goto out;
 
-	if (spc_check_dev_wce(dev))
+	if (se_dev_check_wce(dev))
 		p[2] = 0x04; /* Write Cache Enable */
 	p[12] = 0x20; /* Disabled Read Ahead */
 
@@ -1009,7 +996,7 @@ 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 ((spc_check_dev_wce(dev)) &&
+	if ((se_dev_check_wce(dev)) &&
 	    (dev->dev_attrib.emulate_fua_write > 0))
 		spc_modesense_dpofua(&buf[length], type);
 

include/target/target_core_backend.h

@@ -111,6 +111,7 @@ void	array_free(void *array, int n);
 void	target_core_setup_sub_cits(struct se_subsystem_api *);
 
 /* attribute helpers from target_core_device.c for backend drivers */
+bool	se_dev_check_wce(struct se_device *);
 int	se_dev_set_max_unmap_lba_count(struct se_device *, u32);
 int	se_dev_set_max_unmap_block_desc_count(struct se_device *, u32);
 int	se_dev_set_unmap_granularity(struct se_device *, u32);