filelock/region_locking.c

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

The source code file is copyright 2010, Michael Kerrisk, and is licensed under the GNU Lesser General Public License, version 3.

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Function list (Bold in this list means a function is not static)

/* 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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