filelock/region_locking.c

This is filelock/region_locking.c (Listing 55-3, page 1134), an example from the book, The Linux Programming Interface.

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Cover of The Linux Programming Interface

+/* region_locking.c
+
+   Some useful functions for file region (fcntl()) locking.
+*/
 #include <fcntl.h>
 #include "region_locking.h"             /* Declares functions defined here */
 
 /* Lock a file region (private; public interfaces below) */
 
 static int
 lockReg(int fd, int cmd, int type, int whence, int start, off_t len)
 {
     struct flock fl;
 
     fl.l_type = type;
     fl.l_whence = whence;
     fl.l_start = start;
     fl.l_len = len;
 
     return fcntl(fd, cmd, &fl);
 }
 
 int                     /* Lock a file region using nonblocking F_SETLK */
 lockRegion(int fd, int type, int whence, int start, int len)
 {
     return lockReg(fd, F_SETLK, type, whence, start, len);
 }
 
 int                     /* Lock a file region using blocking F_SETLKW */
 lockRegionWait(int fd, int type, int whence, int start, int len)
 {
     return lockReg(fd, F_SETLKW, type, whence, start, len);
 }
 
 /* Test if a file region is lockable. Return 0 if lockable, or
    PID of process holding incompatible lock, or -1 on error. */
 
 pid_t
 regionIsLocked(int fd, int type, int whence, int start, int len)
 {
     struct flock fl;
 
     fl.l_type = type;
     fl.l_whence = whence;
     fl.l_start = start;
     fl.l_len = len;
 
     if (fcntl(fd, F_GETLK, &fl) == -1)
         return -1;
 
     return (fl.l_type == F_UNLCK) ? 0 : fl.l_pid;
 }

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