gpsee_flock.c

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/**
 *  @file	gpsee_flock.c		Portable advisory file-locking for GPSEE's internal use.
 *  @author	Wes Garland, PageMail, Inc., wes@page.ca
 *  @version	$Id: gpsee_flock.c,v 1.3 2009/07/31 16:46:04 wes Exp $
 *  @date	March 2009
 */

static const char __attribute__((unused)) rcsid[]="$Id: gpsee_flock.c,v 1.3 2009/07/31 16:46:04 wes Exp $:";

#include <gpsee.h>
#if !defined(HAVE_FLOCK) && !defined(NO_GPSEE_FLOCK)

/** Implement advisory file lock with fcntl using flock semantics.
 *
 * @bug	errno codes match fcntl(), not flock(). They're
 *  	not portable anyhow, so more information probably
 *  	won't hurt.
 *
 * @bug	errno will probably never be set to EAWOULDBLOCK
 *  	under Solaris, because I can't figure out how to tell
 *  	whether or not failed because of blocking I/O or
 *  	something else. There does not appear to be an appropriate
 *  	errno return. That's okay, though, because nobody should
 *  	care *why* a non-blocking lock failed, just that it did.
 */
int gpsee_flock(int fd, int lockmode)
{
  int          cmd,
               result;
  struct flock fl;
  
  if (lockmode & GPSEE_LOCK_NB)
    cmd=F_SETLK;
  else
    cmd=F_SETLKW;
 
  memset(&fl, 0, sizeof(fl));

  switch(lockmode & ~GPSEE_LOCK_NB)
  {
    case GPSEE_LOCK_SH:
      fl.l_type = F_RDLCK;
      break;
    case GPSEE_LOCK_EX:
      fl.l_type = F_WRLCK;
      break;      
    case GPSEE_LOCK_UN:
      fl.l_type = F_UNLCK;
      break;      
 }

  fl.l_whence=SEEK_SET;

  result=fcntl(fd, cmd, &fl);
  return(result);
}
#endif