61 lines
3.1 KiB
C
61 lines
3.1 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/assert.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/macros.h"
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#include "libc/sysv/errfuns.h"
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/**
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* Writes to file at offset, thus avoiding superfluous lseek().
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*
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* @param fd is something open()'d earlier, noting pipes might not work
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* @param buf is copied from, cf. copy_file_range(), sendfile(), etc.
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* @param size in range [1..0x7ffff000] is reasonable
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* @param offset is bytes from start of file at which write begins
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* @return [1..size] bytes on success, or -1 w/ errno; noting zero is
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* impossible unless size was passed as zero to do an error check
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* @see pread(), write()
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*/
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ssize_t pwrite(int fd, const void *buf, size_t size, int64_t offset) {
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ssize_t rc;
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size_t wrote;
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if (fd == -1 || offset < 0) return einval();
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size = MIN(size, 0x7ffff000);
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if (!IsWindows()) {
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rc = pwrite$sysv(fd, buf, size, offset);
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} else if (__isfdkind(fd, kFdFile)) {
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rc = write$nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1, offset);
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} else {
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return ebadf();
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}
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if (rc != -1) {
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wrote = (size_t)rc;
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if (wrote == 0) {
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assert(size == 0);
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} else {
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assert(wrote <= size);
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}
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}
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return rc;
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}
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