mirror of
https://github.com/jart/cosmopolitan.git
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91 lines
4.3 KiB
C
91 lines
4.3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et 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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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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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/cp.internal.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/calls/struct/iovec.internal.h"
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#include "libc/calls/syscall-sysv.internal.h"
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#include "libc/dce.h"
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#include "libc/intrin/strace.h"
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#include "libc/intrin/weaken.h"
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#include "libc/macros.h"
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#include "libc/runtime/runtime.h"
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#include "libc/runtime/zipos.internal.h"
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#include "libc/stdio/sysparam.h"
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#include "libc/sysv/errfuns.h"
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/**
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* Reads from file at offset.
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*
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* This function never changes the current position of `fd`.
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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 into, cf. copy_file_range(), sendfile(), etc.
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* @param size is always saturated to 0x7ffff000 automatically
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* @param offset is bytes from start of file at which read begins
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* @return [1..size] bytes on success, 0 on EOF, or -1 w/ errno; with
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* exception of size==0, in which case return zero means no error
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* @raise ESPIPE if `fd` isn't seekable
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* @raise EINVAL if `offset` is negative
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* @raise EBADF if `fd` isn't an open file descriptor
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* @raise EIO if a complicated i/o error happened
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* @raise EINTR if signal was delivered instead
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* @raise ECANCELED if thread was cancelled in masked mode
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* @see pwrite(), write()
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* @cancelationpoint
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* @asyncsignalsafe
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* @vforksafe
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*/
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ssize_t pread(int fd, void *buf, size_t size, int64_t offset) {
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ssize_t rc;
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BEGIN_CANCELATION_POINT;
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// XNU and BSDs will EINVAL if requested bytes exceeds INT_MAX
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// this is inconsistent with Linux which ignores huge requests
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size = MIN(size, 0x7ffff000);
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if (offset < 0) {
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rc = einval();
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} else if (fd < 0) {
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rc = ebadf();
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} else if (__isfdkind(fd, kFdZip)) {
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rc = _weaken(__zipos_read)(
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(struct ZiposHandle *)(intptr_t)g_fds.p[fd].handle,
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(struct iovec[]){{buf, size}}, 1, offset);
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} else if (!IsWindows()) {
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rc = sys_pread(fd, buf, size, offset, offset);
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} else if (__isfdkind(fd, kFdSocket)) {
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rc = espipe();
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} else if (__isfdkind(fd, kFdFile) || __isfdkind(fd, kFdDevNull) ||
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__isfdkind(fd, kFdDevRandom)) {
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rc = sys_read_nt(fd, (struct iovec[]){{buf, size}}, 1, offset);
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} else {
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rc = ebadf();
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}
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npassert(rc == -1 || (size_t)rc <= size);
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END_CANCELATION_POINT;
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DATATRACE("pread(%d, [%#.*hhs%s], %'zu, %'zd) → %'zd% m", fd,
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MAX(0, MIN(40, rc)), buf, rc > 40 ? "..." : "", size, offset, rc);
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return rc;
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}
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__weak_reference(pread, pread64);
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