From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:53394) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SoING-0005if-79 for qemu-devel@nongnu.org; Mon, 09 Jul 2012 14:07:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SoINE-0001Fk-46 for qemu-devel@nongnu.org; Mon, 09 Jul 2012 14:07:53 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:42018) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SoIND-0001FY-Vu for qemu-devel@nongnu.org; Mon, 09 Jul 2012 14:07:52 -0400 Received: from /spool/local by e6.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 9 Jul 2012 14:07:47 -0400 Received: from d01relay07.pok.ibm.com (d01relay07.pok.ibm.com [9.56.227.147]) by d01dlp01.pok.ibm.com (Postfix) with ESMTP id 8C4BE38C806B for ; Mon, 9 Jul 2012 14:02:12 -0400 (EDT) Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay07.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q69I2AMb13434972 for ; Mon, 9 Jul 2012 14:02:10 -0400 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q69I29Re023020 for ; Mon, 9 Jul 2012 15:02:10 -0300 Message-ID: <4FFB1C9F.5070703@linux.vnet.ibm.com> Date: Mon, 09 Jul 2012 14:02:07 -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> <4FFB1657.1090405@linux.vnet.ibm.com> <20120709144842.123febe2@doriath.home> In-Reply-To: <20120709144842.123febe2@doriath.home> 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: Luiz Capitulino Cc: Kevin Wolf , aliguori@us.ibm.com, stefanha@linux.vnet.ibm.com, libvir-list@redhat.com, qemu-devel@nongnu.org, pbonzini@redhat.com, Eric Blake On 07/09/2012 01:48 PM, Luiz Capitulino wrote: > On Mon, 09 Jul 2012 13:35:19 -0400 > Corey Bryant wrote: > >> >> >> 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. > > But then the refcount is associated with the set, not with any particular fd. > Exactly, yes that's what we're doing. Sorry, I thought that was clear in the design overview I sent earlier today. -- Regards, Corey