diff options
| -rw-r--r-- | src/mman/shm_open.c | 6 | ||||
| -rw-r--r-- | src/thread/sem_open.c | 201 |
2 files changed, 99 insertions, 108 deletions
diff --git a/src/mman/shm_open.c b/src/mman/shm_open.c index a9be899b..b23eac7f 100644 --- a/src/mman/shm_open.c +++ b/src/mman/shm_open.c @@ -7,7 +7,7 @@ char *__strchrnul(const char *, int); -static const char *mapname(const char *name, char *buf) +char *__shm_mapname(const char *name, char *buf) { char *p; while (*name == '/') name++; @@ -28,13 +28,13 @@ static const char *mapname(const char *name, char *buf) int shm_open(const char *name, int flag, mode_t mode) { char buf[NAME_MAX+10]; - if (!(name = mapname(name, buf))) return -1; + if (!(name = __shm_mapname(name, buf))) return -1; return open(name, flag|O_NOFOLLOW|O_CLOEXEC|O_NONBLOCK, mode); } int shm_unlink(const char *name) { char buf[NAME_MAX+10]; - if (!(name = mapname(name, buf))) return -1; + if (!(name = __shm_mapname(name, buf))) return -1; return unlink(name); } diff --git a/src/thread/sem_open.c b/src/thread/sem_open.c index 2e900eb3..08f98c25 100644 --- a/src/thread/sem_open.c +++ b/src/thread/sem_open.c @@ -11,164 +11,155 @@ #include <sys/stat.h> #include <stdlib.h> #include <pthread.h> +#include "libc.h" + +char *__shm_mapname(const char *, char *); static struct { ino_t ino; sem_t *sem; int refcnt; } *semtab; +static int lock[2]; -static int semcnt; -static pthread_spinlock_t lock; -static pthread_once_t once; - -static void init() -{ - semtab = calloc(sizeof *semtab, SEM_NSEMS_MAX); -} - -static sem_t *find_map(ino_t ino) -{ - int i; - for (i=0; i<SEM_NSEMS_MAX && semtab[i].ino != ino; i++); - if (i==SEM_NSEMS_MAX) return 0; - if (semtab[i].refcnt == INT_MAX) return (sem_t *)-1; - semtab[i].refcnt++; - return semtab[i].sem; -} +#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; sem_t newsem; void *map; char tmp[64]; struct timespec ts; struct stat st; - int i; + char buf[NAME_MAX+10]; - while (*name=='/') name++; - if (strchr(name, '/')) { - errno = EINVAL; + if (!(name = __shm_mapname(name, buf))) return SEM_FAILED; - } - pthread_once(&once, init); - if (!semtab) { - errno = ENOMEM; + 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, 1, 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|O_CLOEXEC, mode); - if (tfd<0) return SEM_FAILED; - dir = open("/dev/shm", O_DIRECTORY|O_RDONLY|O_CLOEXEC); - 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); - pthread_spin_lock(&lock); + /* 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; + } for (;;) { - if (!(flags & O_EXCL)) { - fd = shm_open(name, flags&~O_CREAT, 0); - if (fd >= 0 || errno != ENOENT) { - if (flags & O_CREAT) { - close(dir); - close(tfd); - unlink(tmp); - } - if (fd >= 0 && fstat(fd, &st) < 0) { + /* 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); - fd = -1; - } - if (fd < 0) { - pthread_spin_unlock(&lock); return SEM_FAILED; } - if ((map = find_map(st.st_ino))) { - pthread_spin_unlock(&lock); - close(fd); - if (map == (sem_t *)-1) - return SEM_FAILED; - return map; - } + close(fd); break; } + if (errno != ENOENT) + return SEM_FAILED; } - if (!(flags & O_CREAT)) { - pthread_spin_unlock(&lock); + if (!(flags & O_CREAT)) return SEM_FAILED; + 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; + return SEM_FAILED; + } + sem_init(&newsem, 1, value); } - if (!linkat(AT_FDCWD, tmp, dir, name, 0)) { - fd = tfd; - close(dir); - unlink(tmp); - break; + /* 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; + return SEM_FAILED; } - 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; } - } - if (fstat(fd, &st) < 0) { - pthread_spin_unlock(&lock); close(fd); - return SEM_FAILED; - } - if (semcnt == SEM_NSEMS_MAX) { - pthread_spin_unlock(&lock); - close(fd); - errno = EMFILE; - return SEM_FAILED; + 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)) + return SEM_FAILED; } - for (i=0; i<SEM_NSEMS_MAX && semtab[i].sem; i++); - map = mmap(0, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); - close(fd); - if (map == MAP_FAILED) { - pthread_spin_unlock(&lock); - 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[i].refcnt++; + UNLOCK(lock); + return semtab[i].sem; } - semtab[i].ino = st.st_ino; - semtab[i].sem = map; - semtab[i].refcnt = 1; - pthread_spin_unlock(&lock); + semtab[slot].refcnt = 1; + semtab[slot].sem = map; + semtab[slot].ino = st.st_ino; + UNLOCK(lock); + return map; } int sem_close(sem_t *sem) { int i; - pthread_spin_lock(&lock); + 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; } - pthread_spin_unlock(&lock); - return munmap(sem, sizeof *sem); + UNLOCK(lock); + munmap(sem, sizeof *sem); + return 0; } |