cosmopolitan/libc/calls/pread.c

60 lines
3.2 KiB
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 │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program is distributed in the hope that it will be useful, but │
│ WITHOUT ANY WARRANTY; without even the implied warranty of │
│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/assert.h"
#include "libc/bits/weaken.h"
#include "libc/calls/calls.h"
#include "libc/calls/internal.h"
#include "libc/calls/struct/iovec.h"
#include "libc/dce.h"
#include "libc/macros.h"
#include "libc/runtime/runtime.h"
#include "libc/sysv/errfuns.h"
#include "libc/zipos/zipos.internal.h"
/**
* Reads from file at offset, thus avoiding superfluous lseek().
*
* @param fd is something open()'d earlier, noting pipes might not work
* @param buf is copied into, cf. copy_file_range(), sendfile(), etc.
* @param size in range [1..0x7ffff000] is reasonable
* @param offset is bytes from start of file at which read begins
* @return [1..size] bytes on success, 0 on EOF, or -1 w/ errno; with
* exception of size==0, in which case return zero means no error
* @see pwrite(), write()
*/
ssize_t pread(int fd, void *buf, size_t size, int64_t offset) {
ssize_t rc;
if (fd == -1 || offset < 0) return einval();
if (__isfdkind(fd, kFdZip)) {
rc = weaken(__zipos_read)(
(struct ZiposHandle *)(intptr_t)g_fds.p[fd].handle, buf, size, offset);
} else if (!IsWindows()) {
rc = pread$sysv(fd, buf, size, offset);
} else if (__isfdkind(fd, kFdFile)) {
rc = read$nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1, offset);
} else {
rc = ebadf();
}
if (!IsTrustworthy() && rc != -1) {
if ((size_t)rc > size) abort();
}
return rc;
}