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glibc  2.9
lockf.c File Reference
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
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int lockf (int fd, int cmd, off_t len)

Function Documentation

int lockf ( int  fd,
int  cmd,
off_t  len 

Definition at line 28 of file lockf.c.

  struct flock fl;

  memset ((char *) &fl, '\0', sizeof (fl));

  /* lockf is always relative to the current file position.  */
  fl.l_whence = SEEK_CUR;
  fl.l_start = 0;
  fl.l_len = len;

  switch (cmd)
    case F_TEST:
      /* Test the lock: return 0 if FD is unlocked or locked by this process;
        return -1, set errno to EACCES, if another process holds the lock.  */
      fl.l_type = F_RDLCK;
      if (__fcntl (fd, F_GETLK, &fl) < 0)
       return -1;
      if (fl.l_type == F_UNLCK || fl.l_pid == __getpid ())
       return 0;
      __set_errno (EACCES);
      return -1;

    case F_ULOCK:
      fl.l_type = F_UNLCK;
      cmd = F_SETLK;
    case F_LOCK:
      fl.l_type = F_WRLCK;
      cmd = F_SETLKW;
    case F_TLOCK:
      fl.l_type = F_WRLCK;
      cmd = F_SETLK;

      __set_errno (EINVAL);
      return -1;

  /* lockf() is a cancellation point but so is fcntl() if F_SETLKW is
     used.  Therefore we don't have to care about cancellation here,
     the fcntl() function will take care of it.  */
  return __fcntl (fd, cmd, &fl);

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