linux: Add clone3 CLONE_CLEAR_SIGHAND optimization to posix_spawn

The clone3 flag resets all signal handlers of the child not set to
SIG_IGN to SIG_DFL.  It allows to skip most of the sigaction calls
to setup child signal handling, where previously a posix_spawn
had to issue 2 times NSIG sigaction calls (one to obtain the current
disposition and another to set either SIG_DFL or SIG_IGN).

With POSIX_SPAWN_SETSIGDEF the child will setup the signal for the case
where the disposition is SIG_IGN.

The code must handle the fallback where clone3 is not available. This is
done by splitting __clone_internal_fallback from __clone_internal.

Checked on x86_64-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/clone3.h b/sysdeps/unix/sysv/linux/clone3.h
index e4d642e521..451b156405 100644
--- a/sysdeps/unix/sysv/linux/clone3.h
+++ b/sysdeps/unix/sysv/linux/clone3.h
@@ -23,6 +23,13 @@
 #include <stddef.h>
 #include <bits/types.h>
 
+
+/* Flags for the clone3 syscall.  */
+#define CLONE_CLEAR_SIGHAND 0x100000000ULL /* Clear any signal handler and
+					      reset to SIG_DFL.  */
+#define CLONE_INTO_CGROUP 0x200000000ULL /* Clone into a specific cgroup given
+					    the right permissions.  */
+
 /* The unsigned 64-bit and 8-byte aligned integer type.  */
 typedef __U64_TYPE __aligned_uint64_t __attribute__ ((__aligned__ (8)));