flock64

Structure

  #include <fcntl.h>
  
  struct flock64 
  {
     pid_t     l_pid;
     pid_t     l_tid;
     short     l_type; 
     short     l_whence; 
     long      ________spare; 
     off64_t   l_start; 
     off64_t   l_len;
  };
  

Fields

l_pid

Specifies the process ID of the owner of the lock.

l_tid

Specifies the thread ID of the owner of the lock.

l_type

Specifies the lock type:

Flag	Value	Description
F_RDLCK	1	Indicates a read lock, which is a sharable lock
F_WRLCK	2	Indicates a write lock, which is an exclusive lock
F_UNLCK	3	Indicates unlock, which is used to remove a lock.

l_whence

Specifies the flag for the starting offset of the lock:

Flag	Value	Description
SEEK_SET	0	Indicates the start of the file plus the offset
SEEK_CUR	1	Indicates the current position in the file plus the offset
SEEK_END	2	Indicates the end of the file plus the offset

________spare

Unused.

l_start

Specifies the relative offset, in bytes, for the lock.

l_len

Specifies the length for the byte range lock. If zero, specifies until EOF.

Remarks

File locking with the fcntl function is constrained to per-process and is not shared across processes. As long as this remains the case, the value in the l_pid field is a copy of the value in the l_tid field.