[V2 1/4] unshare: add --forward-signals option to argument parser

[Kiran Rangoon <kiranrangoon0@gmail.com>]

Add a new --forward-signals command-line option that will allow
unshare to forward SIGTERM and SIGINT signals from the parent
process to the forked child process.

This commit adds the option parsing infrastructure but does not
implement the signal forwarding logic yet. The flag defaults to 0
(disabled) to maintain backward compatibility.

Signed-off-by: Kiran Rangoon <kiranrangoon0@gmail.com>
---
 sys-utils/unshare.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/sys-utils/unshare.c b/sys-utils/unshare.c
index 5370ab981..7e94b9148 100644
--- a/sys-utils/unshare.c
+++ b/sys-utils/unshare.c
@@ -801,6 +801,7 @@ int main(int argc, char *argv[])
 		OPT_MAPAUTO,
 		OPT_MAPSUBIDS,
 		OPT_OWNER,
+		OPT_FORWARD_SIGNALS,
 	};
 	static const struct option longopts[] = {
 		{ "help",          no_argument,       NULL, 'h'             },
@@ -817,6 +818,7 @@ int main(int argc, char *argv[])
 
 		{ "fork",          no_argument,       NULL, 'f'             },
 		{ "kill-child",    optional_argument, NULL, OPT_KILLCHILD   },
+		{ "forward-signals", no_argument,     NULL, OPT_FORWARD_SIGNALS },
 		{ "mount-proc",    optional_argument, NULL, OPT_MOUNTPROC   },
 		{ "mount-binfmt",  optional_argument, NULL, OPT_MOUNTBINFMT },
 		{ "map-user",      required_argument, NULL, OPT_MAPUSER     },
@@ -843,7 +845,7 @@ int main(int argc, char *argv[])
 
 	int setgrpcmd = SETGROUPS_NONE;
 	int unshare_flags = 0;
-	int c, forkit = 0;
+	int c, forkit = 0, forward_signals = 0;
 	uid_t mapuser = -1, owneruser = -1;
 	gid_t mapgroup = -1, ownergroup = -1;
 	struct map_range *usermap = NULL;
@@ -1015,6 +1017,10 @@ int main(int argc, char *argv[])
 			keepcaps = 1;
 			cap_last_cap(); /* Force last cap to be cached before we fork. */
 			break;
+		case OPT_FORWARD_SIGNALS:
+			forkit = 1;
+			forward_signals = 1;
+			break;
 		case 'S':
 			uid = strtoul_or_err(optarg, _("failed to parse uid"));
 			force_uid = 1;
-- 
2.47.3