1//===-- Linux implementation of select ------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "src/sys/select/select.h"
10
11#include "hdr/types/sigset_t.h"
12#include "hdr/types/struct_timespec.h"
13#include "src/__support/CPP/limits.h"
14#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
15#include "src/__support/common.h"
16#include "src/__support/libc_errno.h"
17#include "src/__support/macros/config.h"
18
19#include <stddef.h> // For size_t
20#include <sys/syscall.h> // For syscall numbers.
21
22namespace LIBC_NAMESPACE_DECL {
23
24struct pselect6_sigset_t {
25 sigset_t *ss;
26 size_t ss_len;
27};
28
29LLVM_LIBC_FUNCTION(int, select,
30 (int nfds, fd_set *__restrict read_set,
31 fd_set *__restrict write_set, fd_set *__restrict error_set,
32 struct timeval *__restrict timeout)) {
33 // Linux has a SYS_select syscall but it is not available on all
34 // architectures. So, we use the SYS_pselect6 syscall which is more
35 // widely available. However, SYS_pselect6 takes a struct timespec argument
36 // instead of a struct timeval argument. Also, it takes an additional
37 // argument which is a pointer to an object of a type defined above as
38 // "pselect6_sigset_t".
39 struct timespec ts {
40 0, 0
41 };
42 if (timeout != nullptr) {
43 // In general, if the tv_sec and tv_usec in |timeout| are correctly set,
44 // then converting tv_usec to nanoseconds will not be a problem. However,
45 // if tv_usec in |timeout| is more than a second, it can lead to overflows.
46 // So, we detect such cases and adjust.
47 constexpr time_t TIME_MAX = cpp::numeric_limits<time_t>::max();
48 if ((TIME_MAX - timeout->tv_sec) < (timeout->tv_usec / 1000000)) {
49 ts.tv_sec = TIME_MAX;
50 ts.tv_nsec = 999999999;
51 } else {
52 ts.tv_sec = timeout->tv_sec + timeout->tv_usec / 1000000;
53 ts.tv_nsec = timeout->tv_usec * 1000;
54 }
55 }
56 pselect6_sigset_t pss{nullptr, sizeof(sigset_t)};
57#if SYS_pselect6
58 int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_pselect6, nfds, read_set,
59 write_set, error_set, &ts, &pss);
60#elif defined(SYS_pselect6_time64)
61 int ret = LIBC_NAMESPACE::syscall_impl<int>(
62 SYS_pselect6_time64, nfds, read_set, write_set, error_set, &ts, &pss);
63#else
64#error "SYS_pselect6 and SYS_pselect6_time64 syscalls not available."
65#endif
66 if (ret < 0) {
67 libc_errno = -ret;
68 return -1;
69 }
70 return ret;
71}
72
73} // namespace LIBC_NAMESPACE_DECL
74

source code of libc/src/sys/select/linux/select.cpp