Re: [Qemu-devel] [libvirt] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option

[Eric Blake <eblake@redhat.com>]

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On 10/11/2012 10:04 AM, Eric Blake wrote:
> Another idea: a hybrid approach - the _first_ -add-fd 4 directly adds 4
> to the set, all other -add-fd 4 end up adding dup(4) instead (well,
> fcntl(F_DUPFD_CLOEXEC), but you get the picture).  That is, do the
> duplicate scanning, and if there is no duplicate, use the fd directly;
> if there IS a duplicate, then put a unique fd number as a copy into the
> remaining sets.  That way, you don't have to do a final close() sweep
> across the -add-fd arguments passed on the command line, and you still
> don't have to worry about duplicated fds across multiple sets causing
> mayhem in qemu_close().

Hmm, you may also need to be careful of corner cases.  If I do:

qemu -add-fd fd=4,set=1 -add-fd fd=4,set=2 -add-fd fd=5,set=3 5<&-

with fd 5 not inherited, then a dup(4) would give 5; you don't want to
accidentally add a copy of fd 4 into set 3, but rather fail because fd 5
was not inherited.

-- 
Eric Blake   eblake@redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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