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Full Discussion: fcntl works in linux but not in mac os x
Top Forums Programming fcntl works in linux but not in mac os x Post 302295174 by newhere on Friday 6th of March 2009 07:40:07 PM
Old 03-06-2009
fcntl works in linux but not in mac os x
Hi,

Unless I am missing some serious differences in Mac and linux in terms of C programming, I dont know why this would happen. Please take a look at the following piece of code fragment:

Code:
bool add_input_to_db(Cons *new_data) {
  // Set the attributes of the lock 	
  struct flock fl = {F_WRLCK, SEEK_SET, 0, 0, 0};	 
  int fd = open(LOGFILE, O_APPEND | O_SYNC | O_CREAT | O_WRONLY, 0600);
  if (fd == -1) {
    perror(LOGFILE);
    return false;
  }
  // Get our PID
  fl.l_pid = getpid();
  // Return false on error
  if (fcntl(fd, F_SETLKW, &fl) < 0){
     perror("fcntl");
     return false;
  }
  FILE *database = fdopen(fd, "a");
  int result = write_questions(new_data, database, false);
  // Set to unlock before closing the file
  fl.l_type = F_UNLCK;
  if (fcntl(fd, F_SETLK, &fl) < 0){
     perror("fcntl");
     return false;
  }
  fclose(database);
  return (bool) result;
}

This function is part of a bigger programs that takes in user input and logs it into a file. As you might see, I am trying to get an write lock on the logfile as soon as it opens and release the lock before the file is closed. When I run it on linux (ubuntu hardy), the program runs without any problems. However, when I run it on my mac (Leopard), I get:
Code:
fcntl: Invalid argument

If someone could explain why this would be, it'd be helpful.

Thanks.
 

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LEARN ABOUT LINUX

vop_advlock

VOP_ADVLOCK(9)						   BSD Kernel Developer's Manual					    VOP_ADVLOCK(9)

NAME

     VOP_ADVLOCK -- advisory record locking

SYNOPSIS

     #include <sys/param.h>
     #include <sys/vnode.h>
     #include <sys/fcntl.h>
     #include <sys/lockf.h>

     int
     VOP_ADVLOCK(struct vnode *vp, caddr_t id, int op, struct flock *fl, int flags);

DESCRIPTION

     The arguments are:

     vp     The vnode being manipulated.

     id     The id token which is changing the lock.

     op     The operation to perform (see fcntl(2)).

     fl     Description of the lock.

     flags  One of more of the following:

		  F_RDLCK  Shared or read lock.
		  F_UNLCK  Unlock.
		  F_WRLCK  Exclusive or write lock.
		  F_WAIT   Wait until lock is granted.
		  F_FLOCK  Use flock(2) semantics for lock.
		  F_POSIX  Use POSIX semantics for lock.

     This entry point manipulates advisory record locks on the file.  Most file systems delegate the work for this call to lf_advlock().

RETURN VALUES

     Zero is returned on success, otherwise an error is returned.

SEE ALSO

     fcntl(2), flock(2), vnode(9)

AUTHORS

     This manual page was written by Doug Rabson.

BSD
								   June 30, 1999							       BSD
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