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There is a theoretical problem of an extreme bug where we can get into deadlock due to command handshaking. Thanks to a pair of pipes, we have a situation where the parent thinks the child reported an error and is waiting for a message from the child to explain the error; but at the same time the child thinks it reported success and is waiting for the parent to acknowledge the success; so both processes are now blocked. Thankfully, I don't think this deadlock is possible without at least one other bug in the code, but I did see exactly that sort of situation prior to commit da831af - I saw a backtrace where a double close bug in the parent caused the parent to read from the wrong fd and assume the child failed, even though the child really sent success. This potential deadlock is not quite like commit 858c247 (a deadlock due to multiple readers on one pipe preventing a write from completing), although the solution is similar - always close unused pipe fds before blocking, rather than after. * src/util/command.c (virCommandHandshakeWait): Close unused fds sooner. (cherry picked from commit 5e8ab3915b5f979f049547565805174ec7cd79b8)
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>