Kernel+Userspace: Implement the accept4() system call

Unlike accept() the new accept4() system call lets the caller specify
flags for the newly accepted socket file descriptor, such as
SOCK_CLOEXEC and SOCK_NONBLOCK.

Kernel/API/Syscall.h

@@ -99,7 +99,7 @@ namespace Kernel {
     S(chmod)                      \
     S(socket)                     \
     S(bind)                       \
-    S(accept)                     \
+    S(accept4)                    \
     S(listen)                     \
     S(connect)                    \
     S(link)                       \
@@ -269,6 +269,13 @@ struct SC_clock_nanosleep_params {
     struct timespec* remaining_sleep;
 };
 
+struct SC_accept4_params {
+    int sockfd;
+    sockaddr* addr;
+    socklen_t* addrlen;
+    int flags;
+};
+
 struct SC_getsockopt_params {
     int sockfd;
     int level;

Kernel/Process.h

@@ -364,7 +364,7 @@ public:
     KResultOr<int> sys$socket(int domain, int type, int protocol);
     KResultOr<int> sys$bind(int sockfd, Userspace<const sockaddr*> addr, socklen_t);
     KResultOr<int> sys$listen(int sockfd, int backlog);
-    KResultOr<int> sys$accept(int sockfd, Userspace<sockaddr*>, Userspace<socklen_t*>);
+    KResultOr<int> sys$accept4(Userspace<const Syscall::SC_accept4_params*>);
     KResultOr<int> sys$connect(int sockfd, Userspace<const sockaddr*>, socklen_t);
     KResultOr<int> sys$shutdown(int sockfd, int how);
     KResultOr<ssize_t> sys$sendmsg(int sockfd, Userspace<const struct msghdr*>, int flags);

Kernel/Syscalls/socket.cpp

@@ -79,10 +79,19 @@ KResultOr<int> Process::sys$listen(int sockfd, int backlog)
     return socket.listen(backlog);
 }
 
-KResultOr<int> Process::sys$accept(int accepting_socket_fd, Userspace<sockaddr*> user_address, Userspace<socklen_t*> user_address_size)
+KResultOr<int> Process::sys$accept4(Userspace<const Syscall::SC_accept4_params*> user_params)
 {
     REQUIRE_PROMISE(accept);
 
+    Syscall::SC_accept4_params params;
+    if (!copy_from_user(&params, user_params))
+        return EFAULT;
+
+    int accepting_socket_fd = params.sockfd;
+    Userspace<sockaddr*> user_address((FlatPtr)params.addr);
+    Userspace<socklen_t*> user_address_size((FlatPtr)params.addrlen);
+    int flags = params.flags;
+
     socklen_t address_size = 0;
     if (user_address && !copy_from_user(&address_size, static_ptr_cast<const socklen_t*>(user_address_size)))
         return EFAULT;
@@ -125,7 +134,12 @@ KResultOr<int> Process::sys$accept(int accepting_socket_fd, Userspace<sockaddr*>
 
     accepted_socket_description_result.value()->set_readable(true);
     accepted_socket_description_result.value()->set_writable(true);
-    m_fds[accepted_socket_fd].set(accepted_socket_description_result.release_value(), 0);
+    if (flags & SOCK_NONBLOCK)
+        accepted_socket_description_result.value()->set_blocking(false);
+    int fd_flags = 0;
+    if (flags & SOCK_CLOEXEC)
+        fd_flags |= FD_CLOEXEC;
+    m_fds[accepted_socket_fd].set(accepted_socket_description_result.release_value(), fd_flags);
 
     // NOTE: Moving this state to Completed is what causes connect() to unblock on the client side.
     accepted_socket->set_setup_state(Socket::SetupState::Completed);

Userland/DevTools/UserspaceEmulator/Emulator.h

@@ -137,7 +137,7 @@ private:
     int virt$getpeername(FlatPtr);
     int virt$select(FlatPtr);
     int virt$get_stack_bounds(FlatPtr, FlatPtr);
-    int virt$accept(int sockfd, FlatPtr address, FlatPtr address_length);
+    int virt$accept4(FlatPtr);
     int virt$bind(int sockfd, FlatPtr address, socklen_t address_length);
     int virt$recvmsg(int sockfd, FlatPtr msg_addr, int flags);
     int virt$sendmsg(int sockfd, FlatPtr msg_addr, int flags);

Userland/DevTools/UserspaceEmulator/Emulator_syscalls.cpp

@@ -168,8 +168,8 @@ u32 Emulator::virt_syscall(u32 function, u32 arg1, u32 arg2, u32 arg3)
         return virt$fchmod(arg1, arg2);
     case SC_fchown:
         return virt$fchown(arg1, arg2, arg3);
-    case SC_accept:
+    case SC_accept4:
-        return virt$accept(arg1, arg2, arg3);
+        return virt$accept4(arg1);
     case SC_setsockopt:
         return virt$setsockopt(arg1);
     case SC_getsockname:
@@ -452,17 +452,20 @@ mode_t Emulator::virt$umask(mode_t mask)
     return syscall(SC_umask, mask);
 }
 
-int Emulator::virt$accept(int sockfd, FlatPtr address, FlatPtr address_length)
+int Emulator::virt$accept4(FlatPtr params_addr)
 {
-    socklen_t host_address_length = 0;
+    Syscall::SC_accept4_params params;
-    mmu().copy_from_vm(&host_address_length, address_length, sizeof(host_address_length));
+    mmu().copy_from_vm(&params, params_addr, sizeof(params));
-    auto host_buffer = ByteBuffer::create_zeroed(host_address_length);
+    sockaddr_storage addr = {};
-    int rc = syscall(SC_accept, sockfd, host_buffer.data(), &host_address_length);
+    socklen_t addrlen;
-    if (rc < 0)
+    mmu().copy_from_vm(&addrlen, (FlatPtr)params.addrlen, sizeof(socklen_t));
-        return rc;
+    VERIFY(addrlen <= sizeof(addr));
-    mmu().copy_to_vm(address, host_buffer.data(), min((socklen_t)host_buffer.size(), host_address_length));
+    int rc = accept4(params.sockfd, (sockaddr*)&addr, &addrlen, params.flags);
-    mmu().copy_to_vm(address_length, &host_address_length, sizeof(host_address_length));
+    if (rc == 0) {
-    return rc;
+        mmu().copy_to_vm((FlatPtr)params.addr, &addr, addrlen);
+        mmu().copy_to_vm((FlatPtr)params.addrlen, &addrlen, sizeof(socklen_t));
+    }
+    return rc < 0 ? -errno : rc;
 }
 
 int Emulator::virt$bind(int sockfd, FlatPtr address, socklen_t address_length)

Userland/Libraries/LibC/sys/socket.cpp

@@ -34,7 +34,13 @@ int listen(int sockfd, int backlog)
 
 int accept(int sockfd, sockaddr* addr, socklen_t* addrlen)
 {
-    int rc = syscall(SC_accept, sockfd, addr, addrlen);
+    return accept4(sockfd, addr, addrlen, 0);
+}
+
+int accept4(int sockfd, sockaddr* addr, socklen_t* addrlen, int flags)
+{
+    Syscall::SC_accept4_params params { sockfd, addr, addrlen, flags };
+    int rc = syscall(SC_accept4, &params);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 

Userland/Libraries/LibC/sys/socket.h

@@ -127,6 +127,7 @@ int socket(int domain, int type, int protocol);
 int bind(int sockfd, const struct sockaddr* addr, socklen_t);
 int listen(int sockfd, int backlog);
 int accept(int sockfd, struct sockaddr*, socklen_t*);
+int accept4(int sockfd, struct sockaddr*, socklen_t*, int);
 int connect(int sockfd, const struct sockaddr*, socklen_t);
 int shutdown(int sockfd, int how);
 ssize_t send(int sockfd, const void*, size_t, int flags);