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



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


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