In daemons using pidfiles to protect against concurrent
execution there is a possibility that a crash may leave a stale
pidfile on disk, which then prevents later restart of the daemon.
To avoid this problem, introduce a pair of APIs which make
use of virFileLock to ensure crash-safe & race condition-safe
pidfile acquisition & releae
* src/libvirt_private.syms, src/util/virpidfile.c,
src/util/virpidfile.h: Add virPidFileAcquire and virPidFileRelease
In some cases the caller of virPidFileRead might like extra checks
to determine whether the pid just read is really the one they are
expecting. This adds virPidFileReadIfAlive which will check whether
the pid is still alive with kill(0, -1), and (on linux only) will
look at /proc/$PID/path
* libvirt_private.syms, util/virpidfile.c, util/virpidfile.h: Add
virPidFileReadIfValid and virPidFileReadPathIfValid
* network/bridge_driver.c: Use new APIs to check PID validity
The functions for manipulating pidfiles are in util/util.{c,h}.
We will shortly be adding some further pidfile related functions.
To avoid further growing util.c, this moves the pidfile related
functions into a dedicated virpidfile.{c,h}. The functions are
also all renamed to have 'virPidFile' as their name prefix
* util/util.h, util/util.c: Remove all pidfile code
* util/virpidfile.c, util/virpidfile.h: Add new APIs for pidfile
handling.
* lxc/lxc_controller.c, lxc/lxc_driver.c, network/bridge_driver.c,
qemu/qemu_process.c: Add virpidfile.h include and adapt for API
renames
