X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=src%2Fthread%2Fsem_open.c;h=ed2353c8ba3afd9ef12b3211c322dfa92ddd805a;hb=4d98280388a21db6913911ff647b2e56338d46cf;hp=55d5ef6b7808bae8e070e1d979d0b67083407375;hpb=6fc5fdbdc70dd17ea8e681a361fb4dae541ee953;p=musl

diff --git a/src/thread/sem_open.c b/src/thread/sem_open.c
index 55d5ef6b..ed2353c8 100644
--- a/src/thread/sem_open.c
+++ b/src/thread/sem_open.c
@@ -9,108 +9,163 @@
 #include <time.h>
 #include <stdio.h>
 #include <sys/stat.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include "libc.h"
 
-static void *find_map(int fd)
-{
-	char c;
-	struct stat st;
-	FILE *f;
-	void *addr;
-	unsigned long long off, ino;
-	char buf[100];
+char *__shm_mapname(const char *, char *);
 
-	if (fstat(fd, &st) < 0) return 0;
-	if (!(f = fopen("/proc/self/maps", "rb"))) return 0;
-	
-	while (fgets(buf, sizeof buf, f)) {
-		sscanf(buf, "%lx-%*lx %*s %llx %*x:%*x %llu /dev/shm%c",
-			(long *)&addr, &off, &ino, &c);
-		while (!strchr(buf, '\n') && fgets(buf, sizeof buf, f));
-		if (c!='/') continue;
-		c = 0;
-		if (!off && st.st_ino == ino) {
-			fclose(f);
-			return addr;
-		}
-	}
-	fclose(f);
-	return 0;
-}
+static struct {
+	ino_t ino;
+	sem_t *sem;
+	int refcnt;
+} *semtab;
+static int lock[2];
+
+#define FLAGS (O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NONBLOCK)
 
 sem_t *sem_open(const char *name, int flags, ...)
 {
 	va_list ap;
 	mode_t mode;
 	unsigned value;
-	int fd, tfd, dir;
+	int fd, i, e, slot, first=1, cnt, cs;
 	sem_t newsem;
 	void *map;
 	char tmp[64];
 	struct timespec ts;
+	struct stat st;
+	char buf[NAME_MAX+10];
 
-	while (*name=='/') name++;
-	if (strchr(name, '/')) {
-		errno = EINVAL;
+	if (!(name = __shm_mapname(name, buf)))
+		return SEM_FAILED;
+
+	LOCK(lock);
+	/* Allocate table if we don't have one yet */
+	if (!semtab && !(semtab = calloc(sizeof *semtab, SEM_NSEMS_MAX))) {
+		UNLOCK(lock);
 		return SEM_FAILED;
 	}
 
-	if (flags & O_CREAT) {
-		va_start(ap, flags);
-		mode = va_arg(ap, mode_t) & 0666;
-		value = va_arg(ap, unsigned);
-		va_end(ap);
-		if (value > SEM_VALUE_MAX) {
-			errno = EINVAL;
-			return SEM_FAILED;
-		}
-		sem_init(&newsem, 0, value);
-		clock_gettime(CLOCK_REALTIME, &ts);
-		snprintf(tmp, sizeof(tmp), "/dev/shm/%p-%p-%d-%d",
-			&name, name, (int)getpid(), (int)ts.tv_nsec);
-		tfd = open(tmp, O_CREAT|O_EXCL|O_RDWR, mode);
-		if (tfd<0) return SEM_FAILED;
-		dir = open("/dev/shm", O_DIRECTORY|O_RDONLY);
-		if (dir<0 || write(tfd,&newsem,sizeof newsem)!=sizeof newsem) {
-			if (dir >= 0) close(dir);
-			close(tfd);
-			unlink(tmp);
-			return SEM_FAILED;
-		}
+	/* Reserve a slot in case this semaphore is not mapped yet;
+	 * this is necessary because there is no way to handle
+	 * failures after creation of the file. */
+	slot = -1;
+	for (cnt=i=0; i<SEM_NSEMS_MAX; i++) {
+		cnt += semtab[i].refcnt;
+		if (!semtab[i].sem && slot < 0) slot = i;
+	}
+	/* Avoid possibility of overflow later */
+	if (cnt == INT_MAX || slot < 0) {
+		errno = EMFILE;
+		UNLOCK(lock);
+		return SEM_FAILED;
 	}
+	/* Dummy pointer to make a reservation */
+	semtab[slot].sem = (sem_t *)-1;
+	UNLOCK(lock);
 
-	flags &= ~O_ACCMODE;
-	flags |= O_RDWR;
+	flags &= (O_CREAT|O_EXCL);
+
+	/* Early failure check for exclusive open; otherwise the case
+	 * where the semaphore already exists is expensive. */
+	if (flags == (O_CREAT|O_EXCL) && access(name, F_OK) == 0) {
+		errno = EEXIST;
+		return SEM_FAILED;
+	}
+
+	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
 
 	for (;;) {
-		if (!(flags & O_EXCL)) {
-			fd = shm_open(name, flags&~O_CREAT, mode);
-			if (fd >= 0 || errno != ENOENT) {
-				if (flags & O_CREAT) {
-					close(dir);
-					close(tfd);
-					unlink(tmp);
+		/* If exclusive mode is not requested, try opening an
+		 * existing file first and fall back to creation. */
+		if (flags != (O_CREAT|O_EXCL)) {
+			fd = open(name, FLAGS);
+			if (fd >= 0) {
+				if ((map = mmap(0, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED ||
+				    fstat(fd, &st) < 0) {
+					close(fd);
+					goto fail;
 				}
-				if (fd < 0) return SEM_FAILED;
-				if ((map = find_map(fd)))
-					return map;
+				close(fd);
 				break;
 			}
+			if (errno != ENOENT)
+				goto fail;
 		}
-		if (!linkat(AT_FDCWD, tmp, dir, name, 0)) {
-			fd = tfd;
-			close(dir);
-			unlink(tmp);
-			break;
+		if (!(flags & O_CREAT))
+			goto fail;
+		if (first) {
+			first = 0;
+			va_start(ap, flags);
+			mode = va_arg(ap, mode_t) & 0666;
+			value = va_arg(ap, unsigned);
+			va_end(ap);
+			if (value > SEM_VALUE_MAX) {
+				errno = EINVAL;
+				goto fail;
+			}
+			sem_init(&newsem, 1, value);
+		}
+		/* Create a temp file with the new semaphore contents
+		 * and attempt to atomically link it as the new name */
+		clock_gettime(CLOCK_REALTIME, &ts);
+		snprintf(tmp, sizeof(tmp), "/dev/shm/tmp-%d", (int)ts.tv_nsec);
+		fd = open(tmp, O_CREAT|O_EXCL|FLAGS, mode);
+		if (fd < 0) {
+			if (errno == EEXIST) continue;
+			goto fail;
 		}
-		if ((flags & O_EXCL) || errno != EEXIST) {
-			close(dir);
-			close(tfd);
+		if (write(fd, &newsem, sizeof newsem) != sizeof newsem || fstat(fd, &st) < 0 ||
+		    (map = mmap(0, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED) {
+			close(fd);
 			unlink(tmp);
-			return SEM_FAILED;
+			goto fail;
 		}
+		close(fd);
+		if (link(tmp, name) == 0) break;
+		e = errno;
+		unlink(tmp);
+		/* Failure is only fatal when doing an exclusive open;
+		 * otherwise, next iteration will try to open the
+		 * existing file. */
+		if (e != EEXIST || flags == (O_CREAT|O_EXCL))
+			goto fail;
 	}
-	map = mmap(0, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
-	close(fd);
-	if (map == MAP_FAILED) return SEM_FAILED;
+
+	/* See if the newly mapped semaphore is already mapped. If
+	 * so, unmap the new mapping and use the existing one. Otherwise,
+	 * add it to the table of mapped semaphores. */
+	LOCK(lock);
+	for (i=0; i<SEM_NSEMS_MAX && semtab[i].ino != st.st_ino; i++);
+	if (i<SEM_NSEMS_MAX) {
+		munmap(map, sizeof(sem_t));
+		semtab[slot].sem = 0;
+		slot = i;
+		map = semtab[i].sem;
+	}
+	semtab[slot].refcnt++;
+	semtab[slot].sem = map;
+	semtab[slot].ino = st.st_ino;
+	UNLOCK(lock);
+	pthread_setcancelstate(cs, 0);
 	return map;
+
+fail:
+	pthread_setcancelstate(cs, 0);
+	return SEM_FAILED;
+}
+
+int sem_close(sem_t *sem)
+{
+	int i;
+	LOCK(lock);
+	for (i=0; i<SEM_NSEMS_MAX && semtab[i].sem != sem; i++);
+	if (!--semtab[i].refcnt) {
+		semtab[i].sem = 0;
+		semtab[i].ino = 0;
+	}
+	UNLOCK(lock);
+	munmap(sem, sizeof *sem);
+	return 0;
 }