Re: [Qemu-devel] [PATCH v6 01/22] block: Add flag bits for image locking

[Kevin Wolf <kwolf@redhat.com>]

Am 03.06.2016 um 10:48 hat Fam Zheng geschrieben:
> Later the block layer will automatically lock the images to avoid unexpected
> concurrent accesses to the same image, which will easily corrupt the metadata
> or user data, unless in some very special cases, like migration.
> 
> The exceptional cases like shared storage migration and testing should
> set BDRV_O_SHARED_LOCK or BDRV_O_NO_LOCK to advise an appropriate
> locking mode.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>

Worth asserting in bdrv_open_common() that BDRV_O_NO_LOCK and
BDRV_O_SHARED_LOCK aren't passed at the same time?

Kevin

>  include/block/block.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/block/block.h b/include/block/block.h
> index 70ea299..02b598b 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -94,6 +94,8 @@ typedef struct HDGeometry {
>                                        select an appropriate protocol driver,
>                                        ignoring the format layer */
>  #define BDRV_O_NO_IO       0x10000 /* don't initialize for I/O */
> +#define BDRV_O_NO_LOCK     0x20000 /* don't lock image file */
> +#define BDRV_O_SHARED_LOCK 0x40000 /* lock the image file in shared mode */
>  
>  #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_NO_FLUSH)
>  
> -- 
> 2.8.2
>