cosmopolitan/libc/calls/pwritev.c

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/*-*- 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
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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.
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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.
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*/
#include "libc/bits/safemacros.h"
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#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().
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*
* @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)) {
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/*
* 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);
}
}