[PATCH 5/7] vfs: Add wbcflush sysfs knob to disable storage devicewriteback cache flushes

[Fernando Luis Vázquez Cao]

Add a sysfs knob to disable storage device writeback cache flushes.

Signed-off-by: Fernando Luis Vazquez Cao <fernando@xxxxxxxxxxxxx>
---

diff -urNp linux-2.6.29-orig/block/blk-barrier.c linux-2.6.29/block/blk-barrier.c
--- linux-2.6.29-orig/block/blk-barrier.c	2009-03-24 08:12:14.000000000 +0900
+++ linux-2.6.29/block/blk-barrier.c	2009-03-30 17:08:28.000000000 +0900
@@ -318,6 +318,9 @@ int blkdev_issue_flush(struct block_devi
 	if (!q)
 		return -ENXIO;

+	if (blk_queue_nowbcflush(q))
+		return -EOPNOTSUPP;
+
 	bio = bio_alloc(GFP_KERNEL, 0);
 	if (!bio)
 		return -ENOMEM;
diff -urNp linux-2.6.29-orig/block/blk-core.c linux-2.6.29/block/blk-core.c
--- linux-2.6.29-orig/block/blk-core.c	2009-03-24 08:12:14.000000000 +0900
+++ linux-2.6.29/block/blk-core.c	2009-03-30 17:08:28.000000000 +0900
@@ -1452,7 +1452,8 @@ static inline void __generic_make_reques
 			goto end_io;
 		}
 		if (bio_barrier(bio) && bio_has_data(bio) &&
-		    (q->next_ordered == QUEUE_ORDERED_NONE)) {
+		    (blk_queue_nowbcflush(q) ||
+		     q->next_ordered == QUEUE_ORDERED_NONE)) {
 			err = -EOPNOTSUPP;
 			goto end_io;
 		}
diff -urNp linux-2.6.29-orig/block/blk-sysfs.c linux-2.6.29/block/blk-sysfs.c
--- linux-2.6.29-orig/block/blk-sysfs.c	2009-03-24 08:12:14.000000000 +0900
+++ linux-2.6.29/block/blk-sysfs.c	2009-03-30 17:08:28.000000000 +0900
@@ -151,6 +151,27 @@ static ssize_t queue_nonrot_store(struct
 	return ret;
 }

+static ssize_t queue_wbcflush_show(struct request_queue *q, char *page)
+{
+	return queue_var_show(!blk_queue_nowbcflush(q), page);
+}
+
+static ssize_t queue_wbcflush_store(struct request_queue *q, const char *page,
+				    size_t count)
+{
+	unsigned long nm;
+	ssize_t ret = queue_var_store(&nm, page, count);
+
+	spin_lock_irq(q->queue_lock);
+	if (nm)
+		queue_flag_clear(QUEUE_FLAG_NOWBCFLUSH , q);
+	else
+		queue_flag_set(QUEUE_FLAG_NOWBCFLUSH , q);
+	spin_unlock_irq(q->queue_lock);
+
+	return ret;
+}
+
 static ssize_t queue_nomerges_show(struct request_queue *q, char *page)
 {
 	return queue_var_show(blk_queue_nomerges(q), page);
@@ -258,6 +279,12 @@ static struct queue_sysfs_entry queue_no
 	.store = queue_nonrot_store,
 };

+static struct queue_sysfs_entry queue_wbcflush_entry = {
+	.attr = {.name = "wbcflush", .mode = S_IRUGO | S_IWUSR },
+	.show = queue_wbcflush_show,
+	.store = queue_wbcflush_store,
+};
+
 static struct queue_sysfs_entry queue_nomerges_entry = {
 	.attr = {.name = "nomerges", .mode = S_IRUGO | S_IWUSR },
 	.show = queue_nomerges_show,
@@ -284,6 +311,7 @@ static struct attribute *default_attrs[]
 	&queue_iosched_entry.attr,
 	&queue_hw_sector_size_entry.attr,
 	&queue_nonrot_entry.attr,
+	&queue_wbcflush_entry.attr,
 	&queue_nomerges_entry.attr,
 	&queue_rq_affinity_entry.attr,
 	&queue_iostats_entry.attr,
diff -urNp linux-2.6.29-orig/include/linux/blkdev.h linux-2.6.29/include/linux/blkdev.h
--- linux-2.6.29-orig/include/linux/blkdev.h	2009-03-24 08:12:14.000000000 +0900
+++ linux-2.6.29/include/linux/blkdev.h	2009-03-30 17:08:28.000000000 +0900
@@ -452,6 +452,7 @@ struct request_queue
 #define QUEUE_FLAG_NONROT      14	/* non-rotational device (SSD) */
 #define QUEUE_FLAG_VIRT        QUEUE_FLAG_NONROT /* paravirt device */
 #define QUEUE_FLAG_IO_STAT     15	/* do IO stats */
+#define QUEUE_FLAG_NOWBCFLUSH  16	/* disable write-back cache flushing */

 #define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
 				 (1 << QUEUE_FLAG_CLUSTER) |		\
@@ -572,6 +573,8 @@ enum {
 #define blk_queue_stopped(q)	test_bit(QUEUE_FLAG_STOPPED, &(q)->queue_flags)
 #define blk_queue_nomerges(q)	test_bit(QUEUE_FLAG_NOMERGES, &(q)->queue_flags)
 #define blk_queue_nonrot(q)	test_bit(QUEUE_FLAG_NONROT, &(q)->queue_flags)
+#define blk_queue_nowbcflush(q)	\
+	test_bit(QUEUE_FLAG_NOWBCFLUSH, &(q)->queue_flags)
 #define blk_queue_io_stat(q)	test_bit(QUEUE_FLAG_IO_STAT, &(q)->queue_flags)
 #define blk_queue_flushing(q)	((q)->ordseq)
 #define blk_queue_stackable(q)	\
--
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