Re: [Qemu-devel] [PATCH] qemu-img info: show nocow info

[Eric Blake <eblake@redhat.com>]

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On 07/02/2014 03:50 AM, Chunyan Liu wrote:
> Add nocow info in 'qemu-img info' output to show whether the file
> currently has NOCOW flag set or not.
> 
> Signed-off-by: Chunyan Liu <cyliu@suse.com>
> ---
>  block/qapi.c         | 25 +++++++++++++++++++++++++
>  qapi/block-core.json |  3 ++-
>  2 files changed, 27 insertions(+), 1 deletion(-)
> 

> +
> +    /* get NOCOW info */
> +    fd = qemu_open(bs->filename, O_RDONLY | O_NONBLOCK);
> +    if (fd >= 0) {
> +        if (ioctl(fd, FS_IOC_GETFLAGS, &attr) == 0 && (attr & FS_NOCOW_FL)) {
> +            info->has_nocow = true;
> +            info->nocow = true;

Better is:

if (ioctl... == 0) {
    info->has_nocow = true;
    info->nocow = !!(attr & FS_NOCOW_FL)
}

to explicitly document the cases where we know nocow works but is not
set (and omitting it in cases where nocow doesn't exist because of the fs)


> +++ b/qapi/block-core.json
> @@ -126,7 +126,8 @@
>             '*backing-filename': 'str', '*full-backing-filename': 'str',
>             '*backing-filename-format': 'str', '*snapshots': ['SnapshotInfo'],
>             '*backing-image': 'ImageInfo',
> -           '*format-specific': 'ImageInfoSpecific' } }
> +           '*format-specific': 'ImageInfoSpecific',
> +           '*nocow': 'bool' } }

Missing documentation. When adding that, remember to add '(since 2.2)'
(or even since 2.1 if you think this is a bug fix that should go in
during hard freeze)

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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