[libvirt] [PATCH] logging: ensure pending I/O is drained before reading position

[Andrea Bolognani]

On Fri, 2018-12-14 at 13:04 +0000, Daniel P. Berrangé wrote:
> The virtualization driver has two connections to the virtlogd daemon,
> one pipe fd for writing to the log file, and one socket fd for making
> RPC calls. The typical sequence is to write some data to the pipe fd and
> then make an RPC call to determine the current log file offset.
> 
> Unfortunately these two operations are not guaranteed to be handling in
> order by virtlogd. The event loop for virtlogd may identify an incoming
> event on both the pipe fd and socket fd in the same iteration of the
> event loop. It is then entirely possible that it will process the socket
> fd RPC call before reading the pending log data from the pipe fd.
> 
> As a result the virtualization driver will get an outdated log file
> offset reported back.
> 
> This can be seen with the QEMU driver where, when a guest fails to
> start, it will randomly include too much data in the error message it
> has fetched from the log file.

It looks like this patch will address

  https://bugzilla.redhat.com/show_bug.cgi?id=1356108

If that's indeed the case, you can consider adding the link to the
commit message before pushing.

-- 
Andrea Bolognani / Red Hat / Virtualization