Re: [Qemu-devel] [PATCH v2 02/15] file-posix: support BDRV_REQ_ALLOCATE

[Eric Blake]

On 06/01/2017 10:14 AM, Anton Nefedov wrote:
> Current write_zeroes implementation is good enough to satisfy this flag too
> 
> Signed-off-by: Anton Nefedov <address@hidden>
> ---
>  block/file-posix.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)

Are we sure that fallocate() is always fast, or are there some file
systems where it is no faster than manually writing zeroes?  I'm worried
that blindly claiming BDRV_REQ_ALLOCATE may fail if we encounter a libc
or kernel-based fallback that takes a slow patch on our behalf.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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