функция fcntl в библиотеке glibs linux.

[лёля 92]

ребята помогите пожалуйста(((ни чего не понимаю(((
#include <errno.h>
#include <fcntl.h>
#include <hurd.h>
#include <hurd/fd.h>
#include <stdarg.h>
#include <sys/file.h>
int
__libc_fcntl (int fd, int cmd, ...)
{
va_list ap;
struct hurd_fd *d;
int result;

d = _hurd_fd_get (fd);

if (d == NULL)
return __hurd_fail (EBADF);

va_start (ap, cmd);

switch (cmd)
{
error_t err;

default: /* Bad command. */
errno = EINVAL;
result = -1;
break;

/* First the descriptor-based commands, which do no RPCs. */

case F_DUPFD: /* Duplicate the file descriptor. */
case F_DUPFD_CLOEXEC:
{
struct hurd_fd *new;
io_t port, ctty;
struct hurd_userlink ulink, ctty_ulink;
int flags;

HURD_CRITICAL_BEGIN;

/* Extract the ports and flags from the file descriptor. */
__spin_lock (&d->port.lock);
flags = d->flags;
ctty = _hurd_port_get (&d->ctty, &ctty_ulink);
port = _hurd_port_locked_get (&d->port, &ulink); /* Unlocks D. */

if (cmd == F_DUPFD_CLOEXEC)
flags |= FD_CLOEXEC;
else

flags &= ~FD_CLOEXEC;


minimum file descriptor number for it. */
new = _hurd_alloc_fd (&result, va_arg (ap, int));
if (new == NULL)
/* _hurd_alloc_fd has set errno. */
result = -1;
else
{

__mach_port_mod_refs (__mach_task_self (), port,
MACH_PORT_RIGHT_SEND, 1);
if (ctty != MACH_PORT_NULL)
__mach_port_mod_refs (__mach_task_self (), ctty,
MACH_PORT_RIGHT_SEND, 1);

/* Install the ports and flags in the new descriptor. */
if (ctty != MACH_PORT_NULL)
_hurd_port_set (&new->ctty, ctty);
new->flags = flags;
_hurd_port_locked_set (&new->port, port); /* Unlocks NEW. */
}

HURD_CRITICAL_END;

_hurd_port_free (&d->port, &ulink, port);
if (ctty != MACH_PORT_NULL)
_hurd_port_free (&d->ctty, &ctty_ulink, port);

break;
}

#define LOCKED(expr) \
HURD_CRITICAL_BEGIN; \
__spin_lock (&d->port.lock); \
if (d->port.port == MACH_PORT_NULL) \
result = __hurd_fail (EBADF); \
else \
result = (expr); \
__spin_unlock (&d->port.lock); \
HURD_CRITICAL_END;

case F_GETFD: /* Get descriptor flags. */
LOCKED (d->flags);
break;

case F_SETFD: /* Set descriptor flags. */
LOCKED ((d->flags = va_arg (ap, int), 0));
break;


/* Now the real io operations, done by RPCs to io servers. */

case F_GETLK:
case F_SETLK:
case F_SETLKW:
{
/* XXX
We need new RPCs to support POSIX.1 fcntl file locking!!
For the time being we support the whole-file case only,
with all kinds of WRONG WRONG WRONG semantics,
by using flock. This is definitely the Wrong Thing,
but it might be better than nothing (?). */
struct flock *fl = va_arg (ap, struct flock *);
va_end (ap);
switch (cmd)
{
case F_GETLK:
errno = ENOSYS;
return -1;
case F_SETLK:
cmd = LOCK_NB;
break;
default:
cmd = 0;
break;
}
switch (fl->l_type)
{
case F_RDLCK: cmd |= LOCK_SH; break;
case F_WRLCK: cmd |= LOCK_EX; break;
case F_UNLCK: cmd |= LOCK_UN; break;
default:
errno = EINVAL;
return -1;
}
switch (fl->l_whence)
{
case SEEK_SET:
if (fl->l_start == 0 && fl->l_len == 0) /* Whole file request. */
break;
/* It seems to be common for applications to lock the first
byte of the file when they are really doing whole-file locking.
So, since it's so wrong already, might as well do that too. */
if (fl->l_start == 0 && fl->l_len == 1)
break;
/* FALLTHROUGH */
case SEEK_CUR:
case SEEK_END:
errno = ENOTSUP;
return -1;
default:
errno = EINVAL;
return -1;
}

return __flock (fd, cmd);
}

case F_GETFL: /* Get per-open flags. */
if (err = HURD_FD_PORT_USE (d, __io_get_openmodes (port, &result)))
result = __hurd_dfail (fd, err);
break;

case F_SETFL: /* Set per-open flags. */
err = HURD_FD_PORT_USE (d, __io_set_all_openmodes (port,
va_arg (ap, int)));
result = err ? __hurd_dfail (fd, err) : 0;
break;

case F_GETOWN: /* Get owner. */
if (err = HURD_FD_PORT_USE (d, __io_get_owner (port, &result)))
result = __hurd_dfail (fd, err);
break;

case F_SETOWN: /* Set owner. */
err = HURD_FD_PORT_USE (d, __io_mod_owner (port, va_arg (ap, pid_t)));
result = err ? __hurd_dfail (fd, err) : 0;
break;
}
va_end (ap);
return result;
}
libc_hidden_def (__libc_fcntl)
weak_alias (__libc_fcntl, __fcntl)
libc_hidden_weak (__fcntl)
weak_alias (__libc_fcntl, fcntl)