74 lines · cpp
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-exception6//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_t20#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 all34 // architectures. So, we use the SYS_pselect6 syscall which is more35 // widely available. However, SYS_pselect6 takes a struct timespec argument36 // instead of a struct timeval argument. Also, it takes an additional37 // argument which is a pointer to an object of a type defined above as38 // "pselect6_sigset_t".39 struct timespec ts {40 0, 041 };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_pselect658 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#else64#error "SYS_pselect6 and SYS_pselect6_time64 syscalls not available."65#endif66 if (ret < 0) {67 libc_errno = -ret;68 return -1;69 }70 return ret;71}72 73} // namespace LIBC_NAMESPACE_DECL74