[libvirt] [PATCH] safezero: fall back to writing zeroes even when resizing

[Michal Privoznik]

On 07.01.2015 16:49, Ján Tomko wrote:
> Remove the resize flag and use the same code path for all callers.
> This flag was added by commit 18f0316 to allow virStorageFileResize
> use 'safezero' while preserving the behavior.
>
> Explicitly return -2 when a fallback to a different method should
> be done, to make the code path more obvious.
>
> Fail immediately when ftruncate fails in the mmap method,
> as we did before commit 18f0316.
> ---
>   src/locking/lock_driver_sanlock.c |  4 ++--
>   src/storage/storage_backend.c     |  2 +-
>   src/util/virfile.c                | 34 ++++++++++++----------------------
>   src/util/virfile.h                |  2 +-
>   src/util/virstoragefile.c         | 13 ++++---------
>   5 files changed, 20 insertions(+), 35 deletions(-)
>

> diff --git a/src/util/virfile.c b/src/util/virfile.c
> index a2bf008..5f56005 100644
> --- a/src/util/virfile.c
> +++ b/src/util/virfile.c

> -int safezero(int fd, off_t offset, off_t len, bool resize)
> +int safezero(int fd, off_t offset, off_t len)
>   {
>       int ret;
>
> -    /* posix_fallocate returns 0 on success or error number on failure,
> -     * but errno is not set so use that to our advantage since we set
> -     * errno to the returned value if we make the call. If we don't make
> -     * the call because it doesn't exist, then errno won't change and
> -     * we can try other methods.
> -     */
> -    errno = 0;
>       ret = safezero_posix_fallocate(fd, offset, len);
> -    if (ret == 0 || errno != 0)
> +    if (ret != -2)
>           return ret;
>
> -    if (resize)
> -        return safezero_sys_fallocate(fd, offset, len);
> -
> -    if (safezero_mmap(fd, offset, len) == 0)
> +    if (safezero_sys_fallocate(fd, offset, len) == 0)
>           return 0;

Aha! So we are sticking with best effort here. If libvirt was built with 
SYS_fallocate defined, but is running under a kernel without the 
syscall, we want to try other methods too. Makes sense.

> +
> +    ret = safezero_mmap(fd, offset, len);
> +    if (ret != -2)
> +        return ret;
>       return safezero_slow(fd, offset, len);
>   }
>

ACK

Michal