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Re: [Qemu-devel] [PATCH v2 3/3] qemu-config: Add new -add-fd command lin
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option |
Date: |
Thu, 11 Oct 2012 09:55:14 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 |
On 10/11/2012 08:45 AM, Corey Bryant wrote:
>> Another missing validation check is for duplicate use. With the monitor
>> command, you ALWAYS have a unique fd (thanks to SCM_RIGHTS). But with
>> the command line, I can type 'qemu -add-fd fd=4,set=1 -add-fd
>> fd=4,set=2'. Oops - I've now corrupted your set layout, unless you
>> validate that every fd requested in -add-fd does not already reside in
>> any existing set.
>>
>
> I don't see this validation check for duplicate use of fd's being
> necessary. Like you say below, in the QMP add-fd case we can add the
> same fd multiple times. So we should be able to add the same fd
> multiple times via the command line. The only difference between QMP
> and command line in this case is that the QMP fd is a dup and therefore
> a different number and the command line fd will be the same fd. I'd
> prefer to leave this alone unless there's a compelling reason to block
> adding of the same fd.
There is a compelling reason to prevent duplicates among your sets:
qemu_close().
Suppose I add fd 4 into set 1 and 2, and then discard set 2 via monitor
commands. Then, when qemu_close() drops the last reference to set 2, it
steps through and calls close() on all fds in that set, including fd 4.
Oops - now set 1 is invalid, because it is tracking a closed fd. And
worse, if qemu then does something else to open a new fd, it will get fd
4 again, and now set 1 will be tracking the WRONG fd.
--
Eric Blake address@hidden +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- Re: [Qemu-devel] [PATCH v2 2/3] monitor: Enable adding an inherited fd to an fd set, (continued)
[Qemu-devel] [PATCH v2 1/3] monitor: Allow add-fd to any specified fd set, Corey Bryant, 2012/10/10
[Qemu-devel] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option, Corey Bryant, 2012/10/10
Re: [Qemu-devel] [libvirt] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option, Eric Blake, 2012/10/11
Re: [Qemu-devel] [libvirt] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option, Eric Blake, 2012/10/11
Re: [Qemu-devel] [libvirt] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option, Corey Bryant, 2012/10/11