initial commit of reap

2 files changed, 151 insertions, 0 deletions

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..fb1f502
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,15 @@
+ALL=reap
+
+CFLAGS=-g -O2 -Wall -Wno-switch -Wextra -Wwrite-strings
+
+DESTDIR=
+PREFIX=/usr/local
+BINDIR=$(PREFIX)/bin
+MANDIR=$(PREFIX)/share/man
+
+all: $(ALL)
+
+clean: FRC
+	rm -f $(ALL)
+
+FRC:
diff --git a/reap.c b/reap.c
new file mode 100644
index 0000000..925b826
--- /dev/null
+++ b/reap.c
@@ -0,0 +1,136 @@
+/*
+ * reap - run process until all its spawned processes are dead
+ *
+ * To the extent possible under law, Leah Neukirchen <leah@vuxu.org>
+ * has waived all copyright and related or neighboring rights to this work.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#include <sys/prctl.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <ctype.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <signal.h>
+
+sig_atomic_t do_reap;
+sig_atomic_t do_wait;
+
+// TERM/INT -> always reap
+// EXIT -> reap (default) or wait
+
+void
+turn_sharp(int sig)
+{
+	do_reap = 1;
+}
+
+// needs CONFIG_PROC_CHILDREN=y (since Linux 4.2), most modern distros have this
+// enabled.
+// the alternatives are terrible (enumerating all pids or scanning /proc)
+int
+reap_children()
+{
+	char buf[128];
+	snprintf(buf, 128, "/proc/%ld/task/%ld/children",
+	    (long)getpid(), (long)getpid());
+	FILE *file = fopen(buf, "r");
+	if (!file) {
+		fprintf(stderr,
+		    "reap: could not open %s: %s\n",
+		    buf, strerror(errno));
+		return 0;
+	}
+
+	int c;
+	int didsth = 0;
+	pid_t pid = 0;
+	while ((c = getc(file)) != EOF) {
+		if (c == ' ') {
+			if (kill(pid, SIGTERM) == 0)
+				didsth = 1;
+			pid = 0;
+		} else if (isdigit(c)) {
+			pid = (pid * 10) + (c - '0');
+		} else {
+			fprintf(stderr,
+			    "reap: weird byte in /children: 0x%02x\n", c);
+			break;
+		}
+	}
+
+	fclose(file);
+	return didsth;
+}
+
+int
+main(int argc, char *argv[]) {
+
+	int c;
+        while ((c = getopt(argc, argv, "+w")) != -1) {
+		switch (c) {
+		case 'w': do_wait = 1; break;
+		default:
+                        fprintf(stderr,
+"Usage: %s [-w] COMMAND...\n"
+"\t-w\twait for main command to finish (default: start reaping)\n",
+                            argv[0]);
+                        exit(1);
+		}
+	}
+
+	if (prctl(PR_SET_CHILD_SUBREAPER, 1) != 0) {
+		fprintf(stderr,
+		    "reap: failed to become subreaper: %s\n", strerror(errno));
+		exit(111);
+	}
+
+	sigaction(SIGINT,  &(struct sigaction){.sa_handler=turn_sharp}, 0);
+	sigaction(SIGTERM, &(struct sigaction){.sa_handler=turn_sharp}, 0);
+
+	pid_t pid, desc;
+
+	pid = fork();
+	if (pid == 0) {  // in child
+		execvp(argv[optind], argv+optind);
+
+                fprintf(stderr, "reap: exec %s: %s\n", argv[1], strerror(errno));
+                exit(111);
+	} else if (pid < 0) {  // fork failed
+		fprintf(stderr, "reap: exec %s: %s\n", argv[1], strerror(errno));
+                exit(111);
+	}
+
+	int wstatus;
+	int exitcode = 111;
+
+	while (1) {
+		if ((desc = waitpid(-1, &wstatus, 0)) == -1) {
+			if (errno == ECHILD)
+				break;
+			else if (errno == EINTR)
+				/* check do_reap below */;
+			else {
+				fprintf(stderr,
+				    "reap: waitpid %s: %s\n", argv[1],
+				    strerror(errno));
+				exit(111);
+			}
+		} else if (desc == pid) {
+			exitcode = WEXITSTATUS(wstatus);
+			if (!do_wait)
+				do_reap = 1;
+		}
+
+		if (do_reap)
+			if (!reap_children())
+				break;
+	}
+
+	exit(exitcode);
+}