On 04/23/2017 09:33 AM, jemmy858...@gmail.com wrote: > From: Lidong Chen <lidongc...@tencent.com> > > is_allocated_sectors_min don't guarantee to contain the > consecutive number of zero bytes. this patch fixes this bug.
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helpful.
>
> Signed-off-by: Lidong Chen <lidongc...@tencent.com>
> ---
> qemu-img.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/qemu-img.c b/qemu-img.c
> index b220cf7..df6d165 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1060,9 +1060,9 @@ static int is_allocated_sectors(const uint8_t *buf, int
> n, int *pnum)
> }
>
> /*
> - * Like is_allocated_sectors, but if the buffer starts with a used sector,
> - * up to 'min' consecutive sectors containing zeros are ignored. This avoids
> - * breaking up write requests for only small sparse areas.
> + * Like is_allocated_sectors, but up to 'min' consecutive sectors
> + * containing zeros are ignored. This avoids breaking up write requests
> + * for only small sparse areas.
> */
> static int is_allocated_sectors_min(const uint8_t *buf, int n, int *pnum,
> int min)
> @@ -1071,11 +1071,12 @@ static int is_allocated_sectors_min(const uint8_t
> *buf, int n, int *pnum,
> int num_checked, num_used;
>
> if (n < min) {
> - min = n;
> + *pnum = n;
> + return 1;
> }
>
> ret = is_allocated_sectors(buf, n, pnum);
> - if (!ret) {
> + if (!ret && *pnum >= min) {
I seem to recall past attempts to try and patch this function, which
were then turned down, although I haven't scrubbed the archives for a
quick URL to point to. I'm worried that there are more subtleties here
than what you realize.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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