/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-â
âvi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :viâ
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â Copyright 2020 Justine Alexandra Roberts Tunney                              â
â                                                                              â
â Permission to use, copy, modify, and/or distribute this software for         â
â any purpose with or without fee is hereby granted, provided that the         â
â above copyright notice and this permission notice appear in all copies.      â
â                                                                              â
â THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                â
â WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                â
â WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             â
â AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         â
â DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        â
â PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               â
â TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             â
â PERFORMANCE OF THIS SOFTWARE.                                                â
ââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââ*/
#include "libc/assert.h"
#include "libc/calls/calls.h"
#include "libc/calls/syscall-nt.internal.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/dce.h"
#include "libc/errno.h"
#include "libc/intrin/strace.internal.h"
#include "libc/str/str.h"
#include "libc/sysv/errfuns.h"

int sys_fadvise_netbsd(int, int, int64_t, int64_t, int) asm("sys_fadvise");

/**
 * Drops hints to O/S about intended I/O behavior.
 *
 * It makes a huge difference. For example, when copying a large file,
 * it can stop the system from persisting GBs of useless memory content.
 *
 * @param len 0 means until end of file
 * @param advice can be POSIX_FADV_SEQUENTIAL, POSIX_FADV_RANDOM, etc.
 * @return 0 on success, or errno on error
 * @raise EBADF if `fd` isn't a valid file descriptor
 * @raise EINVAL if `advice` is invalid or `len` is huge
 * @raise ESPIPE if `fd` refers to a pipe
 * @raise ENOSYS on XNU and OpenBSD
 * @returnserrno
 * @threadsafe
 */
errno_t posix_fadvise(int fd, int64_t offset, int64_t len, int advice) {
  int rc, e = errno;
  if (IsLinux()) {
    rc = sys_fadvise(fd, offset, len, advice);
  } else if (IsFreebsd()) {
    rc = sys_fadvise(fd, offset, len, advice);
    _unassert(rc >= 0);
  } else if (IsNetbsd()) {
    rc = sys_fadvise_netbsd(fd, offset, offset, len, advice);
    _unassert(rc >= 0);
  } else if (IsWindows()) {
    rc = sys_fadvise_nt(fd, offset, len, advice);
  } else {
    rc = enosys();
  }
  if (rc == -1) {
    rc = errno;
    errno = e;
  }
  STRACE("posix_fadvise(%d, %'lu, %'lu, %d) â %s", fd, offset, len, advice,
         !rc ? "0" : _strerrno(rc));
  return rc;
}
