From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:47023) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SoGAN-0003Fg-Qe for qemu-devel@nongnu.org; Mon, 09 Jul 2012 11:46:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SoGAF-0003AL-9c for qemu-devel@nongnu.org; Mon, 09 Jul 2012 11:46:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42232) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SoGAF-00039v-0x for qemu-devel@nongnu.org; Mon, 09 Jul 2012 11:46:19 -0400 Message-ID: <4FFAFCB8.8020508@redhat.com> Date: Mon, 09 Jul 2012 17:46:00 +0200 From: Kevin Wolf 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> In-Reply-To: <4FFAF334.9000807@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 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: Corey Bryant 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 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? 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. 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. > 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. > 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 Kevin