78 lines
3.5 KiB
C
78 lines
3.5 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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│ This program is free software; you can redistribute it and/or modify │
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│ it under the terms of the GNU General Public License as published by │
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│ the Free Software Foundation; version 2 of the License. │
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│ │
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│ This program is distributed in the hope that it will be useful, but │
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│ WITHOUT ANY WARRANTY; without even the implied warranty of │
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│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
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│ General Public License for more details. │
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│ │
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│ You should have received a copy of the GNU General Public License │
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│ along with this program; if not, write to the Free Software │
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│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
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│ 02110-1301 USA │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/bits/bits.h"
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#include "libc/bits/safemacros.h"
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#include "libc/calls/calls.h"
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#include "libc/calls/internal.h"
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#include "libc/calls/struct/iovec.h"
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#include "libc/dce.h"
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#include "libc/errno.h"
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#include "libc/sysv/consts/iov.h"
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#include "libc/sysv/errfuns.h"
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#define __NR_preadv_linux 0x0127
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/**
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* Reads data from multiple buffers from file descriptor at offset.
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*
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* @param count is recommended to be 16 or fewer; if it exceeds IOV_MAX
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* then the extra buffers are simply ignored
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* @return number of bytes actually read, or -1 w/ errno
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*/
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ssize_t preadv(int fd, struct iovec *iovec, int count, int64_t off) {
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static bool once, demodernize;
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int olderr;
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ssize_t rc;
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if (!count) return 0;
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if ((count = min(count, IOV_MAX)) < 0) return einval();
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/*
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* NT, XNU, and 2007-era Linux don't support this system call.
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*/
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if (!once) {
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once = true;
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if (IsLinux() && iovec->iov_len >= __NR_preadv_linux) {
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/*
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* Read size is too large to detect older kernels safely without
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* introducing nontrivial mechanics. We'll try again later.
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*/
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once = false;
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demodernize = true;
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} else {
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olderr = errno;
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rc = preadv$sysv(fd, iovec, count, off);
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if (rc == -1 && errno == ENOSYS) {
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errno = olderr;
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demodernize = true;
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} else if (IsLinux() && rc == __NR_preadv_linux /*RHEL5:CVE-2010-3301*/) {
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demodernize = true;
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} else {
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return rc;
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}
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}
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}
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if (!demodernize) {
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return preadv$sysv(fd, iovec, count, off);
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} else {
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return pread(fd, iovec[0].iov_base, iovec[0].iov_len, off);
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}
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}
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