/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* lib/krb5/os/lock_file.c */
/*
 * Copyright 1990, 1998 by the Massachusetts Institute of Technology.
 * All Rights Reserved.
 *
 * Export of this software from the United States of America may
 *   require a specific license from the United States Government.
 *   It is the responsibility of any person or organization contemplating
 *   export to obtain such a license before exporting.
 *
 * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
 * distribute this software and its documentation for any purpose and
 * without fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright notice and
 * this permission notice appear in supporting documentation, and that
 * the name of M.I.T. not be used in advertising or publicity pertaining
 * to distribution of the software without specific, written prior
 * permission.  Furthermore if you modify this software you must label
 * your software as modified software and not distribute it in such a
 * fashion that it might be confused with the original M.I.T. software.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is" without express
 * or implied warranty.
 */

#include "k5-int.h"
#include <stdio.h>

#if !defined(_WIN32)

/* Unix version...  */

#if HAVE_UNISTD_H
#include <unistd.h>
#endif

#include <errno.h>

#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif

#if defined(HAVE_FCNTL_H) && defined(F_SETLKW) && defined(F_RDLCK)
#define POSIX_FILE_LOCKS

/*
 * Gnu libc bug 20251, fixed in 2.28, breaks OFD lock support on
 * 32-bit platforms.  Work around this bug by explicitly using the
 * fcntl64 system call and struct flock64.
 */
#if defined(__linux__) && __WORDSIZE == 32
#include <sys/syscall.h>
#ifdef SYS_fcntl64
#define USE_FCNTL64
#endif
#endif
#ifdef USE_FCNTL64
/* Use the fcntl64 system call and struct flock64.  (Gnu libc does not
 * define a fcntl64() function, so we must use syscall().) */
#define fcntl(fd, cmd, arg) syscall(SYS_fcntl64, fd, cmd, arg)
typedef struct flock64 fcntl_lock_st;
#else
/* Use regular fcntl() and struct flock. */
typedef struct flock fcntl_lock_st;
#endif

#endif /* defined(HAVE_FCNTL_H) && defined(F_SETLKW) && defined(F_RDLCK) */

#ifdef HAVE_FLOCK
#ifndef sysvimp
#include <sys/file.h>
#endif
#else
#ifndef LOCK_SH
#define LOCK_SH 0
#define LOCK_EX 0
#define LOCK_UN 0
#endif
#endif

#ifdef POSIX_FILE_LOCKS
/*
 * Try to use OFD locks where available (e.g. Linux 3.15 and later).  OFD locks
 * contend with regular POSIX file locks, but are owned by the open file
 * description instead of the process, which is much better for thread safety.
 * Fall back to regular POSIX locks on EINVAL in case we are running with an
 * older kernel than we were built with.
 */
static int
ofdlock(int fd, int cmd, fcntl_lock_st *lock_arg)
{
#ifdef F_OFD_SETLKW
    int st, ofdcmd;

    assert(cmd == F_SETLKW || cmd == F_SETLK);
    ofdcmd = (cmd == F_SETLKW) ? F_OFD_SETLKW : F_OFD_SETLK;
    st = fcntl(fd, ofdcmd, lock_arg);
    if (st == 0 || errno != EINVAL)
        return st;
#endif
    return fcntl(fd, cmd, lock_arg);
}
#endif /* POSIX_FILE_LOCKS */

/*ARGSUSED*/
krb5_error_code
krb5_lock_file(krb5_context context, int fd, int mode)
{
    int                 lock_flag = -1;
    krb5_error_code     retval = 0;
#ifdef POSIX_FILE_LOCKS
    int lock_cmd = F_SETLKW;
    fcntl_lock_st lock_arg = { 0 };
#endif

    switch (mode & ~KRB5_LOCKMODE_DONTBLOCK) {
    case KRB5_LOCKMODE_SHARED:
#ifdef POSIX_FILE_LOCKS
        lock_arg.l_type = F_RDLCK;
#endif
        lock_flag = LOCK_SH;
        break;
    case KRB5_LOCKMODE_EXCLUSIVE:
#ifdef POSIX_FILE_LOCKS
        lock_arg.l_type = F_WRLCK;
#endif
        lock_flag = LOCK_EX;
        break;
    case KRB5_LOCKMODE_UNLOCK:
#ifdef POSIX_FILE_LOCKS
        lock_arg.l_type = F_UNLCK;
#endif
        lock_flag = LOCK_UN;
        break;
    }

    if (lock_flag == -1)
        return(KRB5_LIBOS_BADLOCKFLAG);

    if (mode & KRB5_LOCKMODE_DONTBLOCK) {
#ifdef POSIX_FILE_LOCKS
        lock_cmd = F_SETLK;
#endif
#ifdef HAVE_FLOCK
        lock_flag |= LOCK_NB;
#endif
    }

#ifdef POSIX_FILE_LOCKS
    lock_arg.l_whence = 0;
    lock_arg.l_start = 0;
    lock_arg.l_len = 0;
    if (ofdlock(fd, lock_cmd, &lock_arg) == -1) {
        if (errno == EACCES || errno == EAGAIN) /* see POSIX/IEEE 1003.1-1988,
                                                   6.5.2.4 */
            return(EAGAIN);
        if (errno != EINVAL)    /* Fall back to flock if we get EINVAL */
            return(errno);
        retval = errno;
    } else
        return 0;           /* We succeeded.  Yay. */
#endif

#ifdef HAVE_FLOCK
    if (flock(fd, lock_flag) == -1)
        retval = errno;
#endif

    return retval;
}
#else   /* Windows or Macintosh */

krb5_error_code
krb5_lock_file(context, fd, mode)
    krb5_context context;
    int fd;
    int mode;
{
    return 0;
}
#endif