nsz Git - musl/blob - src/thread/sem_open.c

   1 #include <semaphore.h>
   2 #include <sys/mman.h>
   3 #include <limits.h>
   4 #include <fcntl.h>
   5 #include <unistd.h>
   6 #include <string.h>
   7 #include <stdarg.h>
   8 #include <errno.h>
   9 #include <time.h>
  10 #include <stdio.h>
  11 #include <sys/stat.h>
  12
  13 static void *find_map(int fd)
  14 {
  15         char c;
  16         struct stat st;
  17         FILE *f;
  18         void *addr;
  19         unsigned long long off, ino;
  20         char buf[100];
  21
  22         if (fstat(fd, &st) < 0) return 0;
  23         if (!(f = fopen("/proc/self/maps", "rb"))) return 0;
  24
  25         while (fgets(buf, sizeof buf, f)) {
  26                 sscanf(buf, "%lx-%*lx %*s %llx %*x:%*x %llu /dev/shm%c",
  27                         (long *)&addr, &off, &ino, &c);
  28                 while (!strchr(buf, '\n') && fgets(buf, sizeof buf, f));
  29                 if (c!='/') continue;
  30                 c = 0;
  31                 if (!off && st.st_ino == ino) {
  32                         fclose(f);
  33                         return addr;
  34                 }
  35         }
  36         fclose(f);
  37         return 0;
  38 }
  39
  40 sem_t *sem_open(const char *name, int flags, ...)
  41 {
  42         va_list ap;
  43         mode_t mode;
  44         unsigned value;
  45         int fd, tfd, dir;
  46         sem_t newsem;
  47         void *map;
  48         char tmp[64];
  49         struct timespec ts;
  50
  51         while (*name=='/') name++;
  52         if (strchr(name, '/')) {
  53                 errno = EINVAL;
  54                 return SEM_FAILED;
  55         }
  56
  57         if (flags & O_CREAT) {
  58                 va_start(ap, flags);
  59                 mode = va_arg(ap, mode_t) & 0666;
  60                 value = va_arg(ap, unsigned);
  61                 va_end(ap);
  62                 if (value > SEM_VALUE_MAX) {
  63                         errno = EINVAL;
  64                         return SEM_FAILED;
  65                 }
  66                 sem_init(&newsem, 0, value);
  67                 clock_gettime(CLOCK_REALTIME, &ts);
  68                 snprintf(tmp, sizeof(tmp), "/dev/shm/%p-%p-%d-%d",
  69                         &name, name, (int)getpid(), (int)ts.tv_nsec);
  70                 tfd = open(tmp, O_CREAT|O_EXCL|O_RDWR, mode);
  71                 if (tfd<0) return SEM_FAILED;
  72                 dir = open("/dev/shm", O_DIRECTORY|O_RDONLY);
  73                 if (dir<0 || write(tfd,&newsem,sizeof newsem)!=sizeof newsem) {
  74                         if (dir >= 0) close(dir);
  75                         close(tfd);
  76                         unlink(tmp);
  77                         return SEM_FAILED;
  78                 }
  79         }
  80
  81         flags &= ~O_ACCMODE;
  82         flags |= O_RDWR;
  83
  84         for (;;) {
  85                 if (!(flags & O_EXCL)) {
  86                         fd = shm_open(name, flags&~O_CREAT, mode);
  87                         if (fd >= 0 || errno != ENOENT) {
  88                                 if (flags & O_CREAT) {
  89                                         close(dir);
  90                                         close(tfd);
  91                                         unlink(tmp);
  92                                 }
  93                                 if (fd < 0) return SEM_FAILED;
  94                                 if ((map = find_map(fd)))
  95                                         return map;
  96                                 break;
  97                         }
  98                 }
  99                 if (!linkat(AT_FDCWD, tmp, dir, name, 0)) {
 100                         fd = tfd;
 101                         close(dir);
 102                         unlink(tmp);
 103                         break;
 104                 }
 105                 if ((flags & O_EXCL) || errno != EEXIST) {
 106                         close(dir);
 107                         close(tfd);
 108                         unlink(tmp);
 109                         return SEM_FAILED;
 110                 }
 111         }
 112         map = mmap(0, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
 113         close(fd);
 114         if (map == MAP_FAILED) return SEM_FAILED;
 115         return map;
 116 }