On 2015-01-27 at 08:51, Denis V. Lunev wrote:
This efficiently writes zeroes on Linux if the kernel is capable enough.
FALLOC_FL_ZERO_RANGE correctly handles all cases, including and not
including file expansion.
Signed-off-by: Denis V. Lunev <d...@openvz.org>
CC: Kevin Wolf <kw...@redhat.com>
CC: Stefan Hajnoczi <stefa...@redhat.com>
CC: Peter Lieven <p...@kamp.de>
CC: Fam Zheng <f...@redhat.com>
---
block/raw-posix.c | 16 ++++++++++++++--
configure | 19 +++++++++++++++++++
2 files changed, 33 insertions(+), 2 deletions(-)
Okay, now the "ret" in handle_aiocb_write_zeroes() is necessary, so
please disregard my statement about removing it in patch 3.
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 24e1fab..3c35b2f 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -60,7 +60,7 @@
#define FS_NOCOW_FL 0x00800000 /* Do not cow file */
#endif
#endif
-#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+#if defined(CONFIG_FALLOCATE_PUNCH_HOLE) ||
defined(CONFIG_FALLOCATE_ZERO_RANGE)
#include <linux/falloc.h>
#endif
#if defined (__FreeBSD__) || defined(__FreeBSD_kernel__)
@@ -902,7 +902,7 @@ static int translate_err(int err)
return err;
}
-#if defined(CONFIG_FALLOCATE_PUNCH_HOLE)
+#if defined(CONFIG_FALLOCATE_PUNCH_HOLE) ||
defined(CONFIG_FALLOCATE_ZERO_RANGE)
static int do_fallocate(int fd, int mode, off_t offset, off_t len)
{
do {
@@ -955,6 +955,18 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData
*aiocb)
}
#endif
+#ifdef CONFIG_FALLOCATE_ZERO_RANGE
+ if (s->has_write_zeroes) {
+ ret = do_fallocate(s->fd, FALLOC_FL_ZERO_RANGE,
+ aiocb->aio_offset, aiocb->aio_nbytes);
+ if (ret == 0 || ret != -ENOTSUP) {
+ return ret;
+ }
+ s->has_write_zeroes = false;
+ return ret;
+ }
First, you probably want to simply fall through here; right now, you are
immediately failing with -ENOTSUP on the first call, but falling through
on the second call. After this patch, it doesn't make a difference, but
after the next one, it might.
Second, while using s->has_write_zeroes here seems correct to me, I
personally don't like sharing it with handle_aiocb_write_zeroes_block();
and if you do introduce a new flag like "has_zero_range", please don't
make it a bit field (I will give you an R-b regardless of whether you
make it a bit field or not, I just won't like it).
Feel free to keep has_write_zeroes, though, while it doesn't look good
to me it certainly is correct from a technical perspective.
Max