On 10.06.2016 23:59, John Snow wrote: > If a device still has an attached BDS because the medium has not yet > been removed, we will be unable to migrate to a new host because > blk_flush will return an error for that backend. > > Replace the call to blk_is_available to blk_is_inserted to weaken > the check and allow flushes from the backend to work, while still > disallowing flushes from the frontend/device model to work. > > This fixes a regression present in 2.6.0 caused by the following commit: > fe1a9cbc339bb54d20f1ca4c1e8788d16944d5cf > block: Move some bdrv_*_all() functions to BB > > Signed-off-by: John Snow <js...@redhat.com> > --- > block/block-backend.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-)
I'm still not sure we shouldn't do the same for blk_{co,aio}_flush(). I
guess you exclude them here because you specifically want to fix the
issue mentioned in the commit message, but then we could just make
blk_flush_all() ignore an -ENOMEDIUM.
I personally think we should make all blk_*flush() functions use
blk_is_inserted() instead of blk_is_available(). As we have discussed on
IRC, there are probably not that many cases a guest can flush a medium
in an open tray anyway (because the main use case are read-only
CD-ROMs), and even if so, that wouldn't change any data, so even if the
guest can actually flush something on an open tray, I don't think anyone
would complain.
Max
> diff --git a/block/block-backend.c b/block/block-backend.c
> index 34500e6..d1e875e 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -1122,7 +1122,7 @@ int blk_co_flush(BlockBackend *blk)
>
> int blk_flush(BlockBackend *blk)
> {
> - if (!blk_is_available(blk)) {
> + if (!blk_is_inserted(blk)) {
> return -ENOMEDIUM;
> }
>
>
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