On 10/12/2015 05:14 AM, Daniel P. Berrange wrote: > When using regular fork() the child process of course inherits > all the parents' signal handlers. If the child then proceeds > to close() any open file descriptors, it may break some of those > registered signal handlers. The child generally does not want to > ever run any of the signal handlers tha parent may have installed
s/tha/that the/
> in the short time before it exec's. The parent may also have blocked
> various signals which the child process will want enabled.
>
> This introduces a wrapper qemu_fork() that takes care to sanitize
> signal handling across fork. Before forking it blocks all signals
> in the parent thread. After fork returns, the parent unblocks the
> signals and carries on as usual. The child, however, resets all the
> signal handlers back to their defaults before it unblocks signals.
> The child process can now exec the binary in a "clean" signal
> environment.
>
> Signed-off-by: Daniel P. Berrange <berra...@redhat.com>
> ---
> include/qemu/osdep.h | 16 ++++++++++++
> util/oslib-posix.c | 71
> ++++++++++++++++++++++++++++++++++++++++++++++++++++
> util/oslib-win32.c | 9 +++++++
> 3 files changed, 96 insertions(+)
Looks very similar to libvirt's fork() wrapper :)
> + for (i = 1; i < NSIG; i++) {
> + /* Only possible errors are EFAULT or EINVAL The former
> + * won't happen, the latter we expect, so no need to check
> + * return value */
> + (void)sigaction(i, &sig_action, NULL);
> + }
Libvirt gets to rely on gnulib for a guaranteed definition of NSIG. But
POSIX doesn't document it, and I'm not sure whether it is present on all
platforms qemu targets. I guess we'll find out soon enough.
Reviewed-by: Eric Blake <ebl...@redhat.com>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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