From c9e4f2c16ea032e9359b0203a2a11973d172ace7 Mon Sep 17 00:00:00 2001
From: Natanael Copa <ncopa@alpinelinux.org>
Date: Thu, 12 Mar 2015 15:55:08 +0100
Subject: forward the events to a helper process via pipe

To reduce number of forks we pass over the events to a helper program
via a pipe. when there are no events for a certain time the helper
program can exit to save memory. Once new events arrives the nldev
application will respawn the helper.
---
 nldev.c | 132 ++++++++++++++++++++++++++++------------------------------------
 1 file changed, 58 insertions(+), 74 deletions(-)

(limited to 'nldev.c')

diff --git a/nldev.c b/nldev.c
index eab53ff..f859eed 100644
--- a/nldev.c
+++ b/nldev.c
@@ -24,10 +24,15 @@
 #include "arg.h"
 #include "log.h"
 
-char *argv0;
 int listfd = -1;
 int dofork = 0;
 
+struct handler {
+	int fd;
+	int argc;
+	char **argv;
+};
+
 void
 disableoom(void)
 {
@@ -47,30 +52,34 @@ disableoom(void)
 }
 
 void
-child(char *runpath)
+spawn_handler(struct handler *child)
 {
-	int fd, pid;
-
-	if (!(pid = fork())) {
-		if (dofork && !dodebug) {
-			fd = open("/dev/null", O_RDWR);
-			if (fd >= 0) {
-				dup2(fd, 1);
-				dup2(fd, 2);
-				if (fd > 2)
-					close(fd);
-			}
-		}
+	int pipefd[2];
+
+	if (pipe(pipefd) == -1)
+		edie("pipe");
+
+	pid_t pid = fork();
 
-		dbg("running %s", runpath);
-		if (execlp(runpath, basename(runpath), NULL) < 0)
-			edie("execvp");
-		exit(0);
-	}
 	if (pid < 0)
 		edie("fork");
 
-	waitpid(pid, NULL, 0);
+	if (pid == 0) {
+		close(pipefd[1]);
+		dup2(pipefd[0], 0);
+		execv(child->argv[0], child->argv);
+		edie("execl");
+	}
+	close(pipefd[0]);
+	child->fd = pipefd[1];
+}
+
+int
+write_to_handler(struct handler *child, const char *buf, size_t count)
+{
+	if (child->fd == -1)
+		spawn_handler(child);
+	return write(child->fd, buf, count);
 }
 
 void
@@ -143,26 +152,25 @@ init_netlink_socket(void)
 void
 usage(void)
 {
-	die("usage: %s [-hdb] [-ku] [-f subsystem] [-r run]\n", argv0);
+	die("usage: %s [-hdb] [-ku] [-- run [...]]\n", argv0);
 }
 
 int
 main(int argc, char *argv[])
 {
 	struct sockaddr_nl cnls;
-	struct pollfd fds;
+	struct pollfd fds[2];
 	struct msghdr hdr;
 	struct iovec iov;
-	char buf[4097], *subsystem, *runpath, *key, *value,
-	     cbuf[CMSG_SPACE(sizeof(struct ucred))];
+	char buf[4097], cbuf[CMSG_SPACE(sizeof(struct ucred))];
 	struct cmsghdr *chdr;
 	struct ucred *cred;
-	int i, len, slen, showudev, showkernel;
+	int len, showudev, showkernel;
+
+	struct handler child;
 
 	showkernel = 1;
 	showudev = 1;
-	subsystem = NULL;
-	runpath = "/bin/mdev";
 
 	ARGBEGIN {
 	case 'b':
@@ -171,25 +179,27 @@ main(int argc, char *argv[])
 	case 'd':
 		dodebug = 1;
 		break;
-	case 'f':
-		subsystem = EARGF(usage());
-		break;
 	case 'k':
 		showudev = 0;
 		break;
 	case 'u':
 		showkernel = 0;
 		break;
-	case 'r':
-		runpath = EARGF(usage());
-		break;
 	default:
 		usage();
 	} ARGEND;
 
-	fds.events = POLLIN;
-	fds.fd = init_netlink_socket();
-	listfd = fds.fd;
+	child.fd = -1;
+	child.argc = argc;
+	child.argv = argv;
+
+	fds[0].events = POLLIN;
+	fds[0].fd = init_netlink_socket();
+
+	fds[1].fd = child.fd;
+	fds[1].events = POLLERR;
+
+	listfd = fds[0].fd;
 
 	if (dofork) {
 		if (daemon(0, 0) < 0)
@@ -201,9 +211,15 @@ main(int argc, char *argv[])
 	disableoom();
 
 	buf[sizeof(buf)-1] = '\0';
-	while (poll(&fds, 1, -1) > -1) {
-		clearenv();
-		setenv("PATH", "/sbin:/bin", 1);
+	while (poll(fds, 2, -1) > -1) {
+		if (fds[1].revents & POLLERR) {
+			dbg("handler exited");
+			close(child.fd);
+			fds[1].fd = child.fd = -1;
+		}
+
+		if (!(fds[0].revents & POLLIN))
+			continue;
 
 		iov.iov_base = &buf;
 		iov.iov_len = sizeof(buf);
@@ -215,7 +231,7 @@ main(int argc, char *argv[])
 		hdr.msg_name = &cnls;
 		hdr.msg_namelen = sizeof(cnls);
 
-		len = recvmsg(fds.fd, &hdr, 0);
+		len = recvmsg(fds[0].fd, &hdr, 0);
 		if (len < 0) {
 			if (errno == EINTR)
 				continue;
@@ -255,40 +271,8 @@ main(int argc, char *argv[])
 			if (cnls.nl_pid > 0)
 				continue;
 		}
-
-		slen = 0;
-		for (i = 0; i < len; i += slen + 1) {
-			key = buf + i;
-			value = strchr(key, '=');
-			slen = strlen(buf+i);
-
-			if (!slen || value == NULL)
-				continue;
-			if (subsystem && !strncmp(key, "SUBSYSTEM=", 10)
-					&& !strstr(key+10, subsystem)) {
-				dbg("subsystem filter '%s' applied.",
-						subsystem);
-				break;
-			}
-
-			value[0] = '\0';
-			value++;
-
-			/*
-			 * We generally trust the kernel. But there
-			 * might be some udev flaw. (It's >20k sloc!)
-			 */
-			if (strcmp(key, "PATH")) {
-				setenv(key, value, 1);
-				dbg("%s = \"%s\"", key, value);
-			}
-		}
-		if (getenv("ACTION") != NULL &&
-				getenv("DEVPATH") != NULL &&
-				getenv("SUBSYSTEM") != NULL &&
-				getenv("SEQNUM") != NULL) {
-			child(runpath);
-		}
+		write_to_handler(&child, buf, len);
+		fds[1].fd = child.fd;
 	}
 
 	shutdown(listfd, SHUT_RDWR);
-- 
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