Screwed up qemu-devel@nongnu.org, sorry for the inconvenience.
Markus Armbruster <arm...@redhat.com> writes:
> bdrv_is_inserted() returns false when:
>
> /**
> * Return TRUE if the media is present
> */
> bool bdrv_is_inserted(BlockDriverState *bs)
> {
> BlockDriver *drv = bs->drv;
> BdrvChild *child;
>
> if (!drv) {
> return false;
>
> 1. @bs has no driver (this is how we represent "no medium").
>
> }
> if (drv->bdrv_is_inserted) {
> return drv->bdrv_is_inserted(bs);
>
> 2. Its driver's ->bdrv_is_inserted() returns false. This is how
> passthrough block backends signal "host device has no medium". Right
> now, the only user is "host_cdrom".
>
> }
> QLIST_FOREACH(child, &bs->children, next) {
> if (!bdrv_is_inserted(child->bs)) {
> return false;
>
> 3. Any of its children has no medium. Common use looking through
> filters, which have a single child.
>
> }
> }
> return true;
> }
>
> Makes sense.
>
> Now look at the uses of QERR_DEVICE_HAS_NO_MEDIUM.
>
> * external_snapshot_prepare() in blockdev.c:
>
> if (!bdrv_is_inserted(state->old_bs)) {
> error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
> goto out;
> }
>
> where @device is the device name, i.e. BlockdevSnapshot member @node
> or BlockdevSnapshotSync member @device. Uh-oh: the latter can be
> null. If we can reach the error_setg() then, we crash on some
> systems.
>
> * bdrv_snapshot_delete() and bdrv_snapshot_load_tmp() in
> block/snaphot.c:
>
> if (!drv) {
> error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, bdrv_get_device_name(bs));
> return -ENOMEDIUM;
> }
>
> where @drv is bs->drv.
>
> Why do we check only for 1. here instead of calling
> bdrv_is_inserted()?
