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Re: [Qemu-devel] [PATCH v2] qcow2: Flush image after creation
From: |
Benoît Canet |
Subject: |
Re: [Qemu-devel] [PATCH v2] qcow2: Flush image after creation |
Date: |
Mon, 28 Oct 2013 16:10:48 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Le Thursday 24 Oct 2013 à 20:35:06 (+0200), Max Reitz a écrit :
> Opening the qcow2 image with BDRV_O_NO_FLUSH prevents any flushes during
> the image creation. This means that the image has not yet been flushed
> to disk when qemu-img create exits. This flush is delayed until the next
> operation on the image involving opening it without BDRV_O_NO_FLUSH and
> closing (or directly flushing) it. For large images and/or images with a
> small cluster size and preallocated metadata, this flush may take a
> significant amount of time and may occur unexpectedly.
>
> Reopening the image without BDRV_O_NO_FLUSH right before the end of
> qcow2_create2() results in hoisting the potentially costly flush into
> the image creation, which is expected to take some time (whereas
> successive image operations may be not).
>
> Signed-off-by: Max Reitz <address@hidden>
> Reviewed-by: Eric Blake <address@hidden>
> ---
> v2:
> - implemented Kevin's remarks:
> - left ret = 0; in the code
> - added goto out; in error handling of bdrv_open
> - implemented Eric's remarks:
> - changed indentation of bdrv_open arguments
> - s/preponing/hoisting/ in the commit message
> ---
> block/qcow2.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 01269f9..6e5d98d 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -1584,6 +1584,16 @@ static int qcow2_create2(const char *filename, int64_t
> total_size,
> }
> }
>
> + bdrv_close(bs);
> +
> + /* Reopen the image without BDRV_O_NO_FLUSH to flush it before returning
> */
> + ret = bdrv_open(bs, filename, NULL,
> + BDRV_O_RDWR | BDRV_O_CACHE_WB, drv, &local_err);
> + if (error_is_set(&local_err)) {
> + error_propagate(errp, local_err);
> + goto out;
> + }
> +
> ret = 0;
> out:
> bdrv_unref(bs);
> --
> 1.8.3.1
>
>
Reviewed-by: Benoit Canet <address@hidden>