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virFork() contains bookkeeping that must be done any time a process
forks. Currently this includes:
1) Call virLogLock() prior to fork() and virLogUnlock() just after,
to avoid a deadlock if some other thread happens to hold that lock
during the fork.
2) Reset the logging hooks and send all child process log messages to
stderr.
3) Block all signals prior to fork(), then either a) reset the signal
mask for the parent process, or b) clear the signal mask for the
child process.
Note that the signal mask handling in __virExec erroneously fails to
restore the signal mask when fork() fails. virFork() fixes this
problem.
Other than this, it attempts to behave as closely to fork() as
possible (including preserving errno for the caller), with a couple
exceptions:
1) The return value is 0 (success) or -1 (failure), while the pid is
returned via the pid_t* argument. Like fork(), if pid < 0 there is
no child process, otherwise both the child and the parent will
return to the caller, and both should look at the return value,
which will indicate if some of the extra processing outlined above
encountered an error.
2) If virFork() returns with pid < 0 or with a return value < 0
indicating an error condition, the error has already been
reported. You can log an additional message if you like, but it
isn't necessary, and may be awkwardly extraneous.
Note that virFork()'s child process will *never* call _exit() - if a
child process is created, it will return to the caller.
* util.c util.h: add virFork() function, based on what is currently
done in __virExec().
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>