On Tue, Mar 21, 2017 at 11:16:23AM +0800, Fam Zheng wrote:
> @@ -1713,21 +1714,22 @@ void bdrv_format_default_perms(BlockDriverState *bs,
> BdrvChild *c,
> perm |= BLK_PERM_CONSISTENT_READ;
> shared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
> } else {
> - /* We want consistent read from backing files if the parent needs it.
> + /* We want consistent read and aio context change from backing files
> if
> + * the parent needs it.
> * No other operations are performed on backing files. */
> - perm &= BLK_PERM_CONSISTENT_READ;
> + perm &= BLK_PERM_CONSISTENT_READ | BLK_PERM_AIO_CONTEXT_CHANGE;
>
> - /* If the parent can deal with changing data, we're okay with a
> + /* If the parent can deal with changing aio context, we're okay too;
> + * If the parent can deal with changing data, we're okay with a
> * writable and resizable backing file. */
> /* TODO Require !(perm & BLK_PERM_CONSISTENT_READ), too? */
> + shared &= BLK_PERM_AIO_CONTEXT_CHANGE | BLK_PERM_WRITE;
> if (shared & BLK_PERM_WRITE) {
> - shared = BLK_PERM_WRITE | BLK_PERM_RESIZE;
> - } else {
> - shared = 0;
> + shared |= BLK_PERM_WRITE | BLK_PERM_RESIZE;We already have BLK_PERM_WRITE so we're just adding BLK_PERM_RESIZE. The following is clearer: shared |= BLK_PERM_RESIZE; > } > > shared |= BLK_PERM_CONSISTENT_READ | BLK_PERM_GRAPH_MOD | > - BLK_PERM_WRITE_UNCHANGED; > + BLK_PERM_WRITE_UNCHANGED | BLK_PERM_AIO_CONTEXT_CHANGE; Why was shared &= BLK_PERM_AIO_CONTEXT_CHANGE necessary above if we unconditionally OR it here?
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