src/ignore_read_lock.c

   1 /*
   2  * gcc -ldl -D _GNU_SOURCE -shared -fPIC -o ignore_read_lock.so ignore_read_lock.c
   3  *
   4  */
   5
   6 #include <dlfcn.h>
   7 #include <stdlib.h>
   8 #include <stdio.h>
   9 #include <unistd.h>
  10 #include <string.h>
  11 #include <errno.h>
  12 #include <err.h>
  13 #include <limits.h>
  14 #include <fcntl.h>
  15 #include <stdarg.h>
  16
  17 #define SUCCESS 0
  18 #define MIN(a,b) (((a)<(b))?(a):(b))
  19
  20
  21 int fcntl(int fd, int cmd, ...)
  22 {
  23         va_list vargs;
  24         va_start(vargs, cmd);
  25         void* arg = va_arg(vargs, void*);
  26         void* arg2 = va_arg(vargs, void*);
  27         va_end(vargs);
  28         struct flock *lk = arg;
  29
  30         int (*orig_fcntl)(int, int, ...) = dlsym(RTLD_NEXT, __func__);
  31         int result = orig_fcntl(fd, cmd, arg, arg2);
  32
  33         //warnx("cmd = %d l_type = %d result = %d errno = %d", cmd, lk->l_type, result, errno);
  34
  35         if(cmd == F_SETLK64 && lk->l_type == F_RDLCK && result != SUCCESS && errno == EAGAIN)
  36         {
  37                 char linkpath[PATH_MAX];
  38                 char path[PATH_MAX];
  39                 sprintf(linkpath, "/proc/self/fd/%d", fd);
  40                 ssize_t sz = readlink(linkpath, path, PATH_MAX);
  41                 path[MIN(sz, PATH_MAX-1)] = '\0';
  42                 warnx("%s: failed to acquire read lock, passing by", path);
  43                 result = SUCCESS;
  44         }
  45         return result;
  46 }
  47