There are severe delays with IO requests processing if QEMU is running in
virtual machine or over software defined storage. Such delays potentially
results in unpredictable guest behavior. For example, guests over IDE or
SATA drive could remount filesystem read-only if write is performed
longer than 10 seconds.

Such reports are very complex to process. Some good starting point for this
seems quite reasonable. This patch provides one. It adds logging of such
potentially dangerous long IO operations.

Changed from v2:
- removed accidentally added slirp subproject ID
- added comment describing timeout selection to patch 3

Changes from v1:
- fixed conversions using macros suggested by Stefan
- fixed option declaration
- enabled by default with patch 3

Signed-off-by: Denis V. Lunev <d...@openvz.org>
CC: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
CC: Kevin Wolf <kw...@redhat.com>
CC: Max Reitz <mre...@redhat.com>
CC: Stefan Hajnoczi <stefa...@redhat.com>



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