cosmopolitan/libc/calls/pwritev.c

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

#define __NR_pwritev_linux 0x0128

/**
 * Writes data from multiple buffers to offset.
 *
 * Please note that it's not an error for a short write to happen. This
 * can happen in the kernel if EINTR happens after some of the write has
 * been committed. It can also happen if we need to polyfill this system
 * call using pwrite().
 *
 * @param count is recommended to be 16 or fewer; if it exceeds IOV_MAX
 *     then the extra buffers are simply ignored
 * @return number of bytes actually sent, or -1 w/ errno
 */
ssize_t pwritev(int fd, const struct iovec *iovec, int count, int64_t off) {
  static bool once, demodernize;
  int olderr;
  ssize_t rc;

  if (!count) return 0;
  if ((count = min(count, IOV_MAX)) < 0) return einval();

  /*
   * NT, XNU, and 2007-era Linux don't support this system call.
   */
  if (!once) {
    once = true;
    if (IsModeDbg() || (IsLinux() && iovec->iov_len >= __NR_pwritev_linux)) {
      /*
       * Write size is too large to detect older kernels safely without
       * introducing nontrivial mechanics. We'll try again later.
       */
      once = false;
      demodernize = true;
    } else {
      olderr = errno;
      rc = pwritev$sysv(fd, iovec, count, off);
      if (rc == -1 && errno == ENOSYS) {
        errno = olderr;
        demodernize = true;
      } else if (IsLinux() &&
                 rc == __NR_pwritev_linux /*RHEL5:CVE-2010-3301*/) {
        demodernize = true;
      } else {
        return rc;
      }
    }
  }

  if (!demodernize) {
    return pwritev$sysv(fd, iovec, count, off);
  } else {
    return pwrite(fd, iovec[0].iov_base, iovec[0].iov_len, off);
  }
}