From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49146) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bCqfp-00023Q-Td for qemu-devel@nongnu.org; Tue, 14 Jun 2016 11:54:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bCqfn-0002Dx-MC for qemu-devel@nongnu.org; Tue, 14 Jun 2016 11:54:40 -0400 References: <1465595961-4762-1-git-send-email-jsnow@redhat.com> <905ed66e-9f55-b27f-6a98-1c2a845f3759@redhat.com> From: John Snow Message-ID: Date: Tue, 14 Jun 2016 11:54:30 -0400 MIME-Version: 1.0 In-Reply-To: <905ed66e-9f55-b27f-6a98-1c2a845f3759@redhat.com> Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] block-backend: allow flush on devices with open tray List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Max Reitz , qemu-block@nongnu.org Cc: kwolf@redhat.com, qemu-devel@nongnu.org On 06/14/2016 09:19 AM, Max Reitz wrote: > 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 >> --- >> 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. Yeah, I didn't investigate the full path. Just making the minimal fixes. Is there a concern that this may still leave certain pathways broken when the CDROM tray is open? I don't know of any immediately without digging again. > > 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 > I have difficulty making pragmatic arguments when purity is at stake, but I've already wandered outside of my device model, so I will defer to your judgment. >> 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; >> } >> >> > > Is this a NACK unless I attempt to address the wider design issue?