From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:54233) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SoHsk-00010i-87 for qemu-devel@nongnu.org; Mon, 09 Jul 2012 13:36:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SoHsi-0001zJ-0M for qemu-devel@nongnu.org; Mon, 09 Jul 2012 13:36:21 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:60204) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SoHsh-0001z4-SL for qemu-devel@nongnu.org; Mon, 09 Jul 2012 13:36:19 -0400 Received: from /spool/local by e8.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 9 Jul 2012 13:36:16 -0400 Received: from d01relay03.pok.ibm.com (d01relay03.pok.ibm.com [9.56.227.235]) by d01dlp02.pok.ibm.com (Postfix) with ESMTP id 748E66E8064 for ; Mon, 9 Jul 2012 13:35:20 -0400 (EDT) Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215]) by d01relay03.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q69HZKmX388136 for ; Mon, 9 Jul 2012 13:35:20 -0400 Received: from d01av01.pok.ibm.com (loopback [127.0.0.1]) by d01av01.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q69N6Cbr027736 for ; Mon, 9 Jul 2012 19:06:13 -0400 Message-ID: <4FFB1657.1090405@linux.vnet.ibm.com> Date: Mon, 09 Jul 2012 13:35:19 -0400 From: Corey Bryant MIME-Version: 1.0 References: <1340390174-7493-1-git-send-email-coreyb@linux.vnet.ibm.com> <20120626091004.GA14451@redhat.com> <4FE9A0F0.2050809@redhat.com> <20120626175045.2c7011b3@doriath.home> <4FEA37A9.10707@linux.vnet.ibm.com> <4FEA3D9C.8080205@redhat.com> <4FF21A67.8010100@linux.vnet.ibm.com> <4FF31265.1000308@linux.vnet.ibm.com> <4FF316C9.5020100@redhat.com> <4FF31CFD.7030508@linux.vnet.ibm.com> <4FF325C8.4060401@redhat.com> <4FF33004.5030909@linux.vnet.ibm.com> <4FF33349.10404@redhat.com> <4FF3381D.40101@linux.vnet.ibm.com> <4FF3FA22.6090400@redhat.com> <4FF5AD90.8000305@linux.vnet.ibm.com> <20120709110510.12214347@doriath.home> <4FFAF334.9000807@linux.vnet.ibm.com> <4FFAFCB8.8020508@redhat.com> In-Reply-To: <4FFAFCB8.8020508@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v4 0/7] file descriptor passing using pass-fd List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: aliguori@us.ibm.com, stefanha@linux.vnet.ibm.com, libvir-list@redhat.com, qemu-devel@nongnu.org, Luiz Capitulino , pbonzini@redhat.com, Eric Blake On 07/09/2012 11:46 AM, Kevin Wolf wrote: > Am 09.07.2012 17:05, schrieb Corey Bryant: >> I'm not sure this is an issue with current design. I know things have >> changed a bit as the email threads evolved, so I'll paste the current >> design that I am working from. Please let me know if you still see any >> issues. >> >> FD passing: >> ----------- >> New monitor commands enable adding/removing an fd to/from a set. New >> monitor command query-fdsets enables querying of current monitor fdsets. >> The set of fds should all refer to the same file, with each fd having >> different access flags (ie. O_RDWR, O_RDONLY). qemu_open can then dup >> the fd that has the matching access mode flags. >> >> Design points: >> -------------- >> 1. add-fd >> -> fd is passed via SCM rights and qemu adds fd to first unused fdset >> (e.g. /dev/fdset/1) >> -> add-fd monitor function initializes the monitor inuse flag for the >> fdset to true >> -> add-fd monitor function initializes the remove flag for the fd to false >> -> add-fd returns fdset number and received fd number (e.g fd=3) to caller >> >> 2. drive_add file=/dev/fdset/1 >> -> qemu_open uses the first fd in fdset1 that has access flags matching >> the qemu_open action flags and has remove flag set to false >> -> qemu_open increments refcount for the fdset >> -> Need to make sure that if a command like 'device-add' fails that >> refcount is not incremented >> >> 3. add-fd fdset=1 >> -> fd is passed via SCM rights >> -> add-fd monitor function adds the received fd to the specified fdset >> (or fails if fdset doesn't exist) >> -> add-fd monitor function initializes the remove flag for the fd to false >> -> add-fd returns fdset number and received fd number (e.g fd=4) to caller >> >> 4. block-commit >> -> qemu_open performs "reopen" by using the first fd from the fdset that >> has access flags matching the qemu_open action flags and has remove flag >> set to false >> -> qemu_open increments refcount for the fdset >> -> Need to make sure that if a command like 'block-commit' fails that >> refcount is not incremented >> >> 5. remove-fd fdset=1 fd=4 >> -> remove-fd monitor function fails if fdset doesn't exist >> -> remove-fd monitor function turns on remove flag for fd=4 > > What was again the reason why we keep removed fds in the fdset at all? Because if refcount is > 0 for the fd set, then the fd could be in use by a block device. So we keep it around until refcount is decremented to zero, at which point it is safe to close. > > The removed flag would make sense for a fdset after a hypothetical > close-fdset call because the fdset needs to be kept around until the > last user closes it, but I think removed fds can be deleted immediately. fds in an fd set really need to be kept around until zero block devices reference them. At that point, if '(refcount == 0 && (!inuse || remove))' is true, then we'll officially close the fd. > > I think I might have confused remove-fd and close-fdset in earlier > emails in this thread, so I hope this isn't inconsistent with what I > said before. > Ok no problem. >> 6. qemu_close (need to replace all close calls in block layer with >> qemu_close) >> -> qemu_close decrements refcount for fdset >> -> qemu_close closes all fds that have (refcount == 0 && (!inuse || remove)) >> -> qemu_close frees the fdset if no fds remain in it >> >> 7. disconnecting the QMP monitor >> -> monitor disconnect visits all fdsets on monitor and turns off monitor >> in-use flag for fdset > > And close all fds with refcount == 0. > Yes, this makes sense. It also makes sense to close removed fds with refcount == 0 in the remove-fd function. Basically this will be the same thing we do in qemu_close. We'll close any fds that evaulate the following as true: (refcount == 0 && (!inuse || remove)) >> 8. connecting the QMP monitor >> -> monitor connect visits all fdsets on monitor and turns on monitor >> in-use flag for fdset >> >> 9. query-fdsets >> -> returns all fdsets and fds that don't have remove flag on -- Regards, Corey