Kernel: Remove sys$select() syscall

Now that the userland has a compatiblity wrapper for select(), the
kernel doesn't need to implement this syscall natively. The poll()
interface been around since 1987, any code still using select()
should be slapped silly.

Note: the SerenityOS source tree mostly uses select() and not poll()
despite SerenityOS having support for poll() since early 2019...

Kernel/API/Syscall.h

@@ -150,7 +150,6 @@ enum class NeedsBigProcessLock {
     S(rmdir, NeedsBigProcessLock::Yes)                      \
     S(sched_getparam, NeedsBigProcessLock::Yes)             \
     S(sched_setparam, NeedsBigProcessLock::Yes)             \
-    S(select, NeedsBigProcessLock::Yes)                     \
     S(sendfd, NeedsBigProcessLock::Yes)                     \
     S(sendmsg, NeedsBigProcessLock::Yes)                    \
     S(set_coredump_metadata, NeedsBigProcessLock::Yes)      \
@@ -264,15 +263,6 @@ struct SC_open_params {
     u16 mode;
 };
 
-struct SC_select_params {
-    int nfds;
-    fd_set* readfds;
-    fd_set* writefds;
-    fd_set* exceptfds;
-    const struct timespec* timeout;
-    const u32* sigmask;
-};
-
 struct SC_poll_params {
     struct pollfd* fds;
     unsigned nfds;

Kernel/CMakeLists.txt

@@ -241,7 +241,6 @@ set(KERNEL_SOURCES
     Syscalls/rename.cpp
     Syscalls/rmdir.cpp
     Syscalls/sched.cpp
-    Syscalls/select.cpp
     Syscalls/sendfd.cpp
     Syscalls/setpgid.cpp
     Syscalls/setuid.cpp

Kernel/Process.h

@@ -315,7 +315,6 @@ public:
     ErrorOr<FlatPtr> sys$msyscall(Userspace<void*>);
     ErrorOr<FlatPtr> sys$msync(Userspace<void*>, size_t, int flags);
     ErrorOr<FlatPtr> sys$purge(int mode);
-    ErrorOr<FlatPtr> sys$select(Userspace<const Syscall::SC_select_params*>);
     ErrorOr<FlatPtr> sys$poll(Userspace<const Syscall::SC_poll_params*>);
     ErrorOr<FlatPtr> sys$get_dir_entries(int fd, Userspace<void*>, size_t);
     ErrorOr<FlatPtr> sys$getcwd(Userspace<char*>, size_t);

Kernel/Syscalls/select.cpp

@@ -1,122 +0,0 @@
-/*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-#include <AK/ScopeGuard.h>
-#include <AK/Time.h>
-#include <Kernel/Debug.h>
-#include <Kernel/FileSystem/OpenFileDescription.h>
-#include <Kernel/Process.h>
-
-namespace Kernel {
-
-using BlockFlags = Thread::FileBlocker::BlockFlags;
-
-ErrorOr<FlatPtr> Process::sys$select(Userspace<const Syscall::SC_select_params*> user_params)
-{
-    VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
-    REQUIRE_PROMISE(stdio);
-
-    auto params = TRY(copy_typed_from_user(user_params));
-
-    if (params.nfds < 0)
-        return EINVAL;
-
-    Thread::BlockTimeout timeout;
-    if (params.timeout) {
-        auto timeout_time = TRY(copy_time_from_user(params.timeout));
-        timeout = Thread::BlockTimeout(false, &timeout_time);
-    }
-
-    auto current_thread = Thread::current();
-
-    u32 previous_signal_mask = 0;
-    if (params.sigmask) {
-        sigset_t sigmask_copy;
-        TRY(copy_from_user(&sigmask_copy, params.sigmask));
-        previous_signal_mask = current_thread->update_signal_mask(sigmask_copy);
-    }
-    ScopeGuard rollback_signal_mask([&]() {
-        if (params.sigmask)
-            current_thread->update_signal_mask(previous_signal_mask);
-    });
-
-    fd_set fds_read, fds_write, fds_except;
-
-    size_t bytes_used = ceil_div(params.nfds, 8);
-    if (bytes_used > sizeof(fds_read))
-        return EINVAL;
-
-    if (params.readfds)
-        TRY(copy_from_user(&fds_read, params.readfds, bytes_used));
-
-    if (params.writefds)
-        TRY(copy_from_user(&fds_write, params.writefds, bytes_used));
-
-    if (params.exceptfds)
-        TRY(copy_from_user(&fds_except, params.exceptfds, bytes_used));
-
-    Thread::SelectBlocker::FDVector fds_info;
-    Vector<int, FD_SETSIZE> selected_fds;
-    for (int fd = 0; fd < params.nfds; fd++) {
-        auto block_flags = BlockFlags::None;
-        if (params.readfds && FD_ISSET(fd, &fds_read))
-            block_flags |= BlockFlags::Read;
-        if (params.writefds && FD_ISSET(fd, &fds_write))
-            block_flags |= BlockFlags::Write;
-        if (params.exceptfds && FD_ISSET(fd, &fds_except))
-            block_flags |= BlockFlags::Exception;
-        if (block_flags == BlockFlags::None)
-            continue;
-
-        auto description = TRY(fds().open_file_description(fd));
-        TRY(fds_info.try_append({ move(description), block_flags }));
-        TRY(selected_fds.try_append(fd));
-    }
-
-    if constexpr (IO_DEBUG || POLL_SELECT_DEBUG)
-        dbgln("selecting on {} fds, timeout={}", fds_info.size(), params.timeout);
-
-    if (current_thread->block<Thread::SelectBlocker>(timeout, fds_info).was_interrupted()) {
-        dbgln_if(POLL_SELECT_DEBUG, "select was interrupted");
-        return EINTR;
-    }
-
-    if (params.readfds)
-        FD_ZERO(&fds_read);
-    if (params.writefds)
-        FD_ZERO(&fds_write);
-    if (params.exceptfds)
-        FD_ZERO(&fds_except);
-
-    int marked_fd_count = 0;
-    for (size_t i = 0; i < fds_info.size(); i++) {
-        auto& fd_entry = fds_info[i];
-        if (fd_entry.unblocked_flags == BlockFlags::None)
-            continue;
-        if (params.readfds && has_flag(fd_entry.unblocked_flags, BlockFlags::Read)) {
-            FD_SET(selected_fds[i], &fds_read);
-            marked_fd_count++;
-        }
-        if (params.writefds && has_flag(fd_entry.unblocked_flags, BlockFlags::Write)) {
-            FD_SET(selected_fds[i], &fds_write);
-            marked_fd_count++;
-        }
-        if (params.exceptfds && has_any_flag(fd_entry.unblocked_flags, BlockFlags::Exception)) {
-            FD_SET(selected_fds[i], &fds_except);
-            marked_fd_count++;
-        }
-    }
-
-    if (params.readfds)
-        TRY(copy_to_user(params.readfds, &fds_read, bytes_used));
-    if (params.writefds)
-        TRY(copy_to_user(params.writefds, &fds_write, bytes_used));
-    if (params.exceptfds)
-        TRY(copy_to_user(params.exceptfds, &fds_except, bytes_used));
-    return marked_fd_count;
-}
-
-}