//===-- Linux implementation of select ------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "src/sys/select/select.h"
#include "hdr/types/sigset_t.h"
#include "hdr/types/struct_timespec.h"
#include "src/__support/CPP/limits.h"
#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
#include "src/__support/common.h"
#include "src/__support/macros/config.h"
#include "src/errno/libc_errno.h"
#include <stddef.h> // For size_t
#include <sys/syscall.h> // For syscall numbers.
namespace LIBC_NAMESPACE_DECL {
struct pselect6_sigset_t {
sigset_t *ss;
size_t ss_len;
};
LLVM_LIBC_FUNCTION(int, select,
(int nfds, fd_set *__restrict read_set,
fd_set *__restrict write_set, fd_set *__restrict error_set,
struct timeval *__restrict timeout)) {
// Linux has a SYS_select syscall but it is not available on all
// architectures. So, we use the SYS_pselect6 syscall which is more
// widely available. However, SYS_pselect6 takes a struct timespec argument
// instead of a struct timeval argument. Also, it takes an additional
// argument which is a pointer to an object of a type defined above as
// "pselect6_sigset_t".
struct timespec ts {
0, 0
};
if (timeout != nullptr) {
// In general, if the tv_sec and tv_usec in |timeout| are correctly set,
// then converting tv_usec to nanoseconds will not be a problem. However,
// if tv_usec in |timeout| is more than a second, it can lead to overflows.
// So, we detect such cases and adjust.
constexpr time_t TIME_MAX = cpp::numeric_limits<time_t>::max();
if ((TIME_MAX - timeout->tv_sec) < (timeout->tv_usec / 1000000)) {
ts.tv_sec = TIME_MAX;
ts.tv_nsec = 999999999;
} else {
ts.tv_sec = timeout->tv_sec + timeout->tv_usec / 1000000;
ts.tv_nsec = timeout->tv_usec * 1000;
}
}
pselect6_sigset_t pss{nullptr, sizeof(sigset_t)};
#if SYS_pselect6
int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_pselect6, nfds, read_set,
write_set, error_set, &ts, &pss);
#elif defined(SYS_pselect6_time64)
int ret = LIBC_NAMESPACE::syscall_impl<int>(
SYS_pselect6_time64, nfds, read_set, write_set, error_set, &ts, &pss);
#else
#error "SYS_pselect6 and SYS_pselect6_time64 syscalls not available."
#endif
if (ret < 0) {
libc_errno = -ret;
return -1;
}
return ret;
}
} // namespace LIBC_NAMESPACE_DECL