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Re: [Qemu-block] [PATCH] block: workaround for unaligned byte range in f
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
Re: [Qemu-block] [PATCH] block: workaround for unaligned byte range in fallocate() |
Date: |
Thu, 22 Aug 2019 18:55:18 +0000 |
22.08.2019 21:31, Andrey Shinkevich wrote:
> Revert the commit 118f99442d 'block/io.c: fix for the allocation failure'
> and make better error handling for the file systems that do not support
> fallocate() for the unaligned byte range. Allow falling back to pwrite
> in case fallocate() returns EINVAL.
>
> Suggested-by: Kevin Wolf <address@hidden>
> Suggested-by: Eric Blake <address@hidden>
> Signed-off-by: Andrey Shinkevich <address@hidden>
> ---
> Discussed in email thread with the message ID
> <address@hidden>
>
> block/file-posix.c | 7 +++++++
> block/io.c | 2 +-
> 2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index fbeb006..2c254ff 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1588,6 +1588,13 @@ static int handle_aiocb_write_zeroes(void *opaque)
> if (s->has_write_zeroes) {
> int ret = do_fallocate(s->fd, FALLOC_FL_ZERO_RANGE,
> aiocb->aio_offset, aiocb->aio_nbytes);
> + if (ret == -EINVAL) {
> + /*
> + * Allow falling back to pwrite for file systems that
> + * do not support fallocate() for unaligned byte range.
> + */
> + return -ENOTSUP;
> + }
> if (ret == 0 || ret != -ENOTSUP) {
> return ret;
> }
Hmm stop, you've done exactly what Den was afraid of:
the next line
s->has_write_zeroes = false;
will disable write_zeroes forever.
Something like
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1588,10 +1588,12 @@ static int handle_aiocb_write_zeroes(void *opaque)
if (s->has_write_zeroes) {
int ret = do_fallocate(s->fd, FALLOC_FL_ZERO_RANGE,
aiocb->aio_offset, aiocb->aio_nbytes);
- if (ret == 0 || ret != -ENOTSUP) {
+ if (ret == 0 || (ret != -ENOTSUP && ret != -EINVAL)) {
return ret;
}
- s->has_write_zeroes = false;
+ if (ret == -ENOTSUP) {
+ s->has_write_zeroes = false;
+ }
}
#endif
will work better. So, handle ENOTSUP as "disable write_zeros forever", and
EINVAL as
"don't disable, but fallback to writing zeros". And we need same handling for
following do_fallocate() calls
too (otherwise they again fails with EINVAL which will break the whole thing).
> diff --git a/block/io.c b/block/io.c
> index 56bbf19..58f08cd 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -1558,7 +1558,7 @@ static int coroutine_fn
> bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
> assert(!bs->supported_zero_flags);
> }
>
> - if (ret < 0 && !(flags & BDRV_REQ_NO_FALLBACK)) {
> + if (ret == -ENOTSUP && !(flags & BDRV_REQ_NO_FALLBACK)) {
> /* Fall back to bounce buffer if write zeroes is unsupported */
> BdrvRequestFlags write_flags = flags & ~BDRV_REQ_ZERO_WRITE;
>
>
--
Best regards,
Vladimir