On Thu, Jan 16, 2014 at 10:39:30AM +0100, Kevin Wolf wrote:
> Am 14.01.2014 um 20:12 hat Jeff Cody geschrieben:
> > Having both read-only=on and snapshot=on together does not make sense;
> > currently, the read-only argument is effectively ignored for the
> > temporary snapshot. To prevent confusion, disallow the usage of both
> > 'snapshot=on' and 'read-only=on'.
> >
> > Signed-off-by: Jeff Cody <jc...@redhat.com>
>
> I believe the reason why this was allowed was so that you can use a
> read-only file with -snapshot. It might not be necessary any more since
> I switched -snapshot implementation to modify the options QDict instead
> of manually doing a second bdrv_open().
>
> Did you test that this still works now?
>
Yes, that still works.
> The other question is about this code in bdrv_open_flags():
>
> /*
> * Snapshots should be writable.
> */
> if (bs->is_temporary) {
> open_flags |= BDRV_O_RDWR;
> }
>
> Is this dead code now because the flag is always already set?
>
Yes, that ends up being dead code. From later in blockdev_init():
bdrv_flags |= ro ? 0 : BDRV_O_RDWR;
QINCREF(bs_opts);
ret = bdrv_open(dinfo->bdrv, file, bs_opts, bdrv_flags, drv, &error);
And ro is set from the read-only QemuOpts, that we check in this
patch in conjunction with snapshot. So if read-only=on is not
specified, it is opened r/w by default.
