[libvirt] [PATCH 2/2] qemu: use -incoming fd:n to avoid qemu holding fd indefinitely

[Paolo Bonzini]

On 12/22/2010 11:27 PM, Eric Blake wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=620363
>
> When using -incoming stdio or -incoming exec:cat, qemu keeps the
> stdin fd open long after the migration is complete.  Not to
> mention that exec:cat is horribly inefficient, by doubling the
> I/O and going through a popen interface in qemu.
>
> The new -incoming fd: of qemu 0.12.0 closes the fd after using
> it, and allows us to bypass an intermediary cat process for
> less I/O.
>
> It would also be possible to fix this bug for qemu<  0.12.0, by
> creating a dummy 'cat' process that reads from real fd and writes to a
> pipe, and pass the other end of the pipe into -incoming exec:cat or
> -incoming stdio, at the expense of even more I/O.  I don't know if
> that is worth the patch, though.

Since you are at it, you may also want to replace the usage of netcat 
and Unix sockets with "-incoming fd:" and a one-way pipe.

Paolo