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Date: Fri, 28 Apr 2017 15:45:43 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v15 20/21] file-posix: Add image locking to
 perm operations
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To: Fam Zheng <famz@redhat.com>
Cc: qemu-devel@nongnu.org, eblake@redhat.com, Max Reitz <mreitz@redhat.com>, qemu-block@nongnu.org

Am 26.04.2017 um 05:34 hat Fam Zheng geschrieben:
> This extends the permission bits of op blocker API to external using
> Linux OFD locks.
> 
> Each permission in @perm and @shared_perm is represented by a locked
> byte in the image file.  Requesting a permission in @perm is translated
> to a shared lock of the corresponding byte; rejecting to share the same
> permission is translated to a shared lock of a separate byte. With that,
> we use 2x number of bytes of distinct permission types.
> 
> virtlockd in libvirt locks the first byte, so we do locking from a
> higher offset.
> 
> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Fam Zheng <famz@redhat.com>

>  BlockDriver bdrv_file = {
>      .format_name = "file",
>      .protocol_name = "file",
> @@ -1977,7 +2234,11 @@ BlockDriver bdrv_file = {
>      .bdrv_get_info = raw_get_info,
>      .bdrv_get_allocated_file_size
>                          = raw_get_allocated_file_size,
> -
> +    .bdrv_inactivate = raw_inactivate,
> +    .bdrv_invalidate_cache = raw_invalidate_cache,
> +    .bdrv_check_perm = raw_check_perm,
> +    .bdrv_set_perm   = raw_set_perm,
> +    .bdrv_abort_perm_update = raw_abort_perm_update,
>      .create_opts = &raw_create_opts,
>  };

By the way, is it intentional that we apply locking only to bdrv_file,
but not to bdrv_host_device or bdrv_host_cdrom?

Kevin