On Mon, 04/10 09:57, Stefan Hajnoczi wrote:
> 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?
It's redundant. Will fix both.
Fam
