[PATCH] target: take advantage of REQ_FUA in the iblock backend

[Christoph Hellwig <hch@infradead.org>]

Since 2.6.37-rc barriers have been replaced with the REQ_FLUSH and
REQ_FUA flags.  Both flags work on all devices without a need to check
for barrier functionality.

Use this fact to simplify the iblock code.  Use the REQ_FUA flag when
we report a write cache or if the target set the FUA bit, and remove
all the barrier detection code.

Btw, I think iblock would benefit from sharing a common option with
the file backend for enabling or disabling the option to provide
a voltile write cache to the initiator or not.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: lio-core-2.6/drivers/target/target_core_iblock.c
===================================================================
--- lio-core-2.6.orig/drivers/target/target_core_iblock.c	2010-11-09 11:23:20.921529680 +0100
+++ lio-core-2.6/drivers/target/target_core_iblock.c	2010-11-09 12:16:20.918196346 +0100
@@ -130,8 +130,6 @@ static void *iblock_allocate_virtdevice(
 	return ib_dev;
 }
 
-static int __iblock_do_sync_cache(struct se_device *);
-
 static struct se_device *iblock_create_virtdevice(
 	struct se_hba *hba,
 	struct se_subsystem_dev *se_dev,
@@ -194,14 +192,7 @@ static struct se_device *iblock_create_v
 		goto failed;
 
 	ib_dev->ibd_depth = dev->queue_depth;
-	/*
-	 * Check if the underlying struct block_device supports the
-	 * block/blk-barrier.c:blkdev_issue_flush() call, depending upon
-	 * which the SCSI mode page bits for WriteCache=1 and DPOFUA=1
-	 * will be enabled by TCM Core.
-	 */
-	if (__iblock_do_sync_cache(dev) == 0)
-		ib_dev->ibd_flags |= IBDF_BDEV_ISSUE_FLUSH;
+
 	/*
 	 * Check if the underlying struct block_device request_queue supports
 	 * the QUEUE_FLAG_DISCARD bit for UNMAP/WRITE_SAME in SCSI + TRIM
@@ -352,51 +343,37 @@ static unsigned long long iblock_emulate
 	return blocks_long;
 }
 
-static int __iblock_do_sync_cache(struct se_device *dev)
-{
-	struct iblock_dev *ib_dev = (struct iblock_dev *)dev->dev_ptr;
-	sector_t error_sector;
-	int ret;
-
-	ret = blkdev_issue_flush(ib_dev->ibd_bd, GFP_KERNEL, &error_sector);
-	if (ret != 0) {
-		printk(KERN_ERR "IBLOCK: block_issue_flush() failed: %d "
-			" error_sector: %llu\n", ret,
-			(unsigned long long)error_sector);
-		return -1;
-	}
-	DEBUG_IBLOCK("IBLOCK: Called block_issue_flush()\n");
-	return 0;
-}
-
 /*
- * Called by target_core_transport():transport_emulate_control_cdb()
- * to emulate SYCHRONIZE_CACHE_*
+ * Emulate SYCHRONIZE_CACHE_*
  */
-void iblock_emulate_sync_cache(struct se_task *task)
+static void iblock_emulate_sync_cache(struct se_task *task)
 {
 	struct se_cmd *cmd = TASK_CMD(task);
-	int ret, immed = (T_TASK(cmd)->t_task_cdb[1] & 0x2);
+	struct iblock_dev *ib_dev = cmd->se_dev->dev_ptr;
+	int immed = (T_TASK(cmd)->t_task_cdb[1] & 0x2);
+	sector_t error_sector;
+	int ret;
+
 	/*
 	 * If the Immediate bit is set, queue up the GOOD response
 	 * for this SYNCHRONIZE_CACHE op
 	 */
 	if (immed)
 		transport_complete_sync_cache(cmd, 1);
+
 	/*
-	 * block/blk-barrier.c:block_issue_flush() does not support a
-	 * LBA + Range synchronization method, so for this case we
-	 * have to flush the entire cache.
+	 * blkdev_issue_flush() does not support a specifying a range, so
+	 * we have to flush the entire cache.
 	 */
-	ret = __iblock_do_sync_cache(cmd->se_dev);
-	if (ret < 0) {
-		if (!(immed))
-			transport_complete_sync_cache(cmd, 0);
-		return;
+	ret = blkdev_issue_flush(ib_dev->ibd_bd, GFP_KERNEL, &error_sector);
+	if (ret != 0) {
+		printk(KERN_ERR "IBLOCK: block_issue_flush() failed: %d "
+			" error_sector: %llu\n", ret,
+			(unsigned long long)error_sector);
 	}
 
-	if (!(immed))
-		transport_complete_sync_cache(cmd, 1);
+	if (!immed)
+		transport_complete_sync_cache(cmd, ret == 0);
 }
 
 /*
@@ -405,11 +382,7 @@ void iblock_emulate_sync_cache(struct se
  */
 int iblock_emulated_write_cache(struct se_device *dev)
 {
-	struct iblock_dev *ib_dev = (struct iblock_dev *)dev->dev_ptr;
-	/*
-	 * Only return WCE if ISSUE_FLUSH is supported
-	 */	
-	return (ib_dev->ibd_flags & IBDF_BDEV_ISSUE_FLUSH) ? 1 : 0;
+	return 1;
 }
 
 int iblock_emulated_dpo(struct se_device *dev)
@@ -423,11 +396,7 @@ int iblock_emulated_dpo(struct se_device
  */
 int iblock_emulated_fua_write(struct se_device *dev)
 {
-	struct iblock_dev *ib_dev = (struct iblock_dev *)dev->dev_ptr;
-	/*
-	 * Only return FUA WRITE if ISSUE_FLUSH is supported
-	 */
-	return (ib_dev->ibd_flags & IBDF_BDEV_ISSUE_FLUSH) ? 1 : 0;
+	return 1;
 }
 
 int iblock_emulated_fua_read(struct se_device *dev)
@@ -442,8 +411,22 @@ static int iblock_do_task(struct se_task
 	struct iblock_dev *ibd = (struct iblock_dev *)req->ib_dev;
 	struct request_queue *q = bdev_get_queue(ibd->ibd_bd);
 	struct bio *bio = req->ib_bio, *nbio = NULL;
-	int write = (TASK_CMD(task)->data_direction == DMA_TO_DEVICE);
-	int ret;
+	int rw;
+
+	if (TASK_CMD(task)->data_direction == DMA_TO_DEVICE) {
+		/*
+		 * Force data to disk if we pretend to not have a volatile
+		 * write cache, or the initiator set the Force Unit Access bit.
+		 */
+		if (DEV_ATTRIB(dev)->emulate_write_cache == 0 ||
+		    (DEV_ATTRIB(dev)->emulate_fua_write > 0 &&
+		     T_TASK(task->task_se_cmd)->t_tasks_fua))
+			rw = WRITE_FUA;
+		else
+			rw = WRITE;
+	} else {
+		rw = READ;
+	}
 
 	while (bio) {
 		nbio = bio->bi_next;
@@ -451,30 +434,12 @@ static int iblock_do_task(struct se_task
 		DEBUG_IBLOCK("Calling submit_bio() task: %p bio: %p"
 			" bio->bi_sector: %llu\n", task, bio, bio->bi_sector);
 
-		submit_bio(write, bio);
+		submit_bio(rw, bio);
 		bio = nbio;
 	}
 
 	if (q->unplug_fn)
 		q->unplug_fn(q);
-	/*
-	 * Check for Forced Unit Access WRITE emulation
-	 */
-	if ((DEV_ATTRIB(dev)->emulate_write_cache > 0) &&
-	    (DEV_ATTRIB(dev)->emulate_fua_write > 0) &&
-	    write && T_TASK(task->task_se_cmd)->t_tasks_fua) {
-		/*
-		 * We might need to be a bit smarter here
-		 * and return some sense data to let the initiator
-		 * know the FUA WRITE cache sync failed..?
-		 */
-		ret = __iblock_do_sync_cache(dev);
-		if (ret < 0) {
-			printk(KERN_ERR "__iblock_do_sync_cache()"
-				" failed for FUA Write\n");
-		}
-	}
-
 	return PYX_TRANSPORT_SENT_TO_TRANSPORT;
 }
 
Index: lio-core-2.6/drivers/target/target_core_iblock.h
===================================================================
--- lio-core-2.6.orig/drivers/target/target_core_iblock.h	2010-11-09 11:23:25.454863013 +0100
+++ lio-core-2.6/drivers/target/target_core_iblock.h	2010-11-09 11:23:35.334863016 +0100
@@ -23,7 +23,6 @@ struct iblock_req {
 
 #define IBDF_HAS_UDEV_PATH		0x01
 #define IBDF_HAS_FORCE			0x02
-#define IBDF_BDEV_ISSUE_FLUSH		0x04
 
 struct iblock_dev {
 	unsigned char ibd_udev_path[SE_UDEV_PATH_LEN];