[Patch V3 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>
---
 bash-completion/unshare | 1 +
 sys-utils/unshare.c     | 9 ++++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/bash-completion/unshare b/bash-completion/unshare
index 19eeb8f08..fdd40e5cb 100644
--- a/bash-completion/unshare
+++ b/bash-completion/unshare
@@ -28,6 +28,7 @@ _unshare_module()
 				--cgroup
 				--time
 				--fork
+				--forward-signals
 				--kill-child
 				--keep-caps
 				--mount-proc
diff --git a/sys-utils/unshare.c b/sys-utils/unshare.c
index 5370ab981..8a7a26df2 100644
--- a/sys-utils/unshare.c
+++ b/sys-utils/unshare.c
@@ -769,6 +769,7 @@ static void __attribute__((__noreturn__)) usage(void)
 	fputs(_(" -f, --fork                fork before launching <program>\n"), out);
 	fputs(_(" --kill-child[=<signame>]  when dying, kill the forked child (implies --fork)\n"
 		"                             defaults to SIGKILL\n"), out);
+	fputs(_(" --forward-signals         forward SIGTERM and SIGINT to child (implies --fork)\n"), out);
 	fputs(USAGE_SEPARATOR, out);
 	fputs(_(" --setgroups allow|deny    control the setgroups syscall in user namespaces\n"), out);
 	fputs(_(" --keep-caps               retain capabilities granted in user namespaces\n"), out);
@@ -801,6 +802,7 @@ 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 +819,7 @@ 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 +846,7 @@ 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 +1018,10 @@ 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