[PATCH v2 02/22] nstool: Propagate SIGTERM to processes executed in the namespace

[David Gibson <david@gibson.dropbear.id.au>]

Particularly in shell it's sometimes natural to save the pid from a process
run and later kill it.  If doing this with nstool exec, however, it will
kill nstool itself, not the program it is running, which isn't usually what
you want or expect.

Address this by having nstool propagate SIGTERM to its child process.  It
may make sense to propagate some other signals, but some introduce extra
complications, so we'll worry about them when and if it seems useful.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 test/nstool.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/test/nstool.c b/test/nstool.c
index a6aca981..fc357d8a 100644
--- a/test/nstool.c
+++ b/test/nstool.c
@@ -345,17 +345,39 @@ static int openns(const char *fmt, ...)
 	return fd;
 }
 
+static pid_t sig_pid;
+static void sig_handler(int signum)
+{
+	int err;
+
+	err = kill(sig_pid, signum);
+	if (err)
+		die("Propagating %s: %s\n", strsignal(signum), strerror(errno));
+}
+
 static void wait_for_child(pid_t pid)
 {
-	int status;
+	struct sigaction sa = {
+		.sa_handler = sig_handler,
+		.sa_flags = SA_RESETHAND,
+	};
+	int status, err;
+
+	sig_pid = pid;
+	err = sigaction(SIGTERM, &sa, NULL);
+	if (err)
+		die("sigaction(SIGTERM): %s\n", strerror(errno));
 
 	/* Match the child's exit status, if possible */
 	for (;;) {
 		pid_t rc;
 
 		rc = waitpid(pid, &status, WUNTRACED);
-		if (rc < 0)
+		if (rc < 0) {
+			if (errno == EINTR)
+				continue;
 			die("waitpid() on %d: %s\n", pid, strerror(errno));
+		}
 		if (rc != pid)
 			die("waitpid() on %d returned %d", pid, rc);
 		if (WIFSTOPPED(status)) {
-- 
@@ -345,17 +345,39 @@ static int openns(const char *fmt, ...)
 	return fd;
 }
 
+static pid_t sig_pid;
+static void sig_handler(int signum)
+{
+	int err;
+
+	err = kill(sig_pid, signum);
+	if (err)
+		die("Propagating %s: %s\n", strsignal(signum), strerror(errno));
+}
+
 static void wait_for_child(pid_t pid)
 {
-	int status;
+	struct sigaction sa = {
+		.sa_handler = sig_handler,
+		.sa_flags = SA_RESETHAND,
+	};
+	int status, err;
+
+	sig_pid = pid;
+	err = sigaction(SIGTERM, &sa, NULL);
+	if (err)
+		die("sigaction(SIGTERM): %s\n", strerror(errno));
 
 	/* Match the child's exit status, if possible */
 	for (;;) {
 		pid_t rc;
 
 		rc = waitpid(pid, &status, WUNTRACED);
-		if (rc < 0)
+		if (rc < 0) {
+			if (errno == EINTR)
+				continue;
 			die("waitpid() on %d: %s\n", pid, strerror(errno));
+		}
 		if (rc != pid)
 			die("waitpid() on %d returned %d", pid, rc);
 		if (WIFSTOPPED(status)) {
-- 
2.45.2