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Subject[PATCH 5/5] vfs: Add wbcflush sysfs knob to disable storage device writeback cache flushes
Add a sysfs knob to disable storage device writeback cache flushes.

Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
---

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 2009-03-29 17:55:45.000000000 +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 2009-03-29 18:09:18.000000000 +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 10:21:38.000000000 +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 10:23:34.000000000 +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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