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/errno/libc_errno.h" 17 18 #include <stddef.h> // For size_t 19 #include <sys/syscall.h> // For syscall numbers. 20 21 namespace LIBC_NAMESPACE { 22 23 struct pselect6_sigset_t { 24 sigset_t *ss; 25 size_t ss_len; 26 }; 27 28 LLVM_LIBC_FUNCTION(int, select, 29 (int nfds, fd_set *__restrict read_set, 30 fd_set *__restrict write_set, fd_set *__restrict error_set, 31 struct timeval *__restrict timeout)) { 32 // Linux has a SYS_select syscall but it is not available on all 33 // architectures. So, we use the SYS_pselect6 syscall which is more 34 // widely available. However, SYS_pselect6 takes a struct timespec argument 35 // instead of a struct timeval argument. Also, it takes an additional 36 // argument which is a pointer to an object of a type defined above as 37 // "pselect6_sigset_t". 38 struct timespec ts { 39 0, 0 40 }; 41 if (timeout != nullptr) { 42 // In general, if the tv_sec and tv_usec in |timeout| are correctly set, 43 // then converting tv_usec to nanoseconds will not be a problem. However, 44 // if tv_usec in |timeout| is more than a second, it can lead to overflows. 45 // So, we detect such cases and adjust. 46 constexpr time_t TIME_MAX = cpp::numeric_limits<time_t>::max(); 47 if ((TIME_MAX - timeout->tv_sec) < (timeout->tv_usec / 1000000)) { 48 ts.tv_sec = TIME_MAX; 49 ts.tv_nsec = 999999999; 50 } else { 51 ts.tv_sec = timeout->tv_sec + timeout->tv_usec / 1000000; 52 ts.tv_nsec = timeout->tv_usec * 1000; 53 } 54 } 55 pselect6_sigset_t pss{nullptr, sizeof(sigset_t)}; 56 #if SYS_pselect6 57 int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_pselect6, nfds, read_set, 58 write_set, error_set, &ts, &pss); 59 #elif defined(SYS_pselect6_time64) 60 int ret = LIBC_NAMESPACE::syscall_impl<int>( 61 SYS_pselect6_time64, nfds, read_set, write_set, error_set, &ts, &pss); 62 #else 63 #error "SYS_pselect6 and SYS_pselect6_time64 syscalls not available." 64 #endif 65 if (ret < 0) { 66 libc_errno = -ret; 67 return -1; 68 } 69 return ret; 70 } 71 72 } // namespace LIBC_NAMESPACE 73