From 24fd8fb16f0779d2bfd172192b0d24c25444fad4 Mon Sep 17 00:00:00 2001
From: sin-ack <sin-ack@users.noreply.github.com>
Date: Mon, 7 Feb 2022 11:03:34 +0000
Subject: [PATCH] Kernel: Ensure socket is suitable for writing in sys$sendmsg

Previously we would return a bytes written value of 0 if the writing end
of the socket was full. Now we either exit with EAGAIN if the socket
description is non-blocking, or block until the description can be
written to.

This is mostly a copy of the conditions in sys$write but with the "total
nwritten" parts removed as sys$sendmsg does not have that.
---
 Kernel/Syscalls/socket.cpp | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/Kernel/Syscalls/socket.cpp b/Kernel/Syscalls/socket.cpp
index a8f15e02ab..b522513d48 100644
--- a/Kernel/Syscalls/socket.cpp
+++ b/Kernel/Syscalls/socket.cpp
@@ -196,12 +196,29 @@ ErrorOr<FlatPtr> Process::sys$sendmsg(int sockfd, Userspace<const struct msghdr*
     auto description = TRY(open_file_description(sockfd));
     if (!description->is_socket())
         return ENOTSOCK;
+
     auto& socket = *description->socket();
     if (socket.is_shut_down_for_writing())
         return EPIPE;
     auto data_buffer = TRY(UserOrKernelBuffer::for_user_buffer((u8*)iovs[0].iov_base, iovs[0].iov_len));
-    auto bytes_sent = TRY(socket.sendto(*description, data_buffer, iovs[0].iov_len, flags, user_addr, addr_length));
-    return bytes_sent;
+
+    while (true) {
+        while (!description->can_write()) {
+            if (!description->is_blocking()) {
+                return EAGAIN;
+            }
+
+            auto unblock_flags = Thread::FileBlocker::BlockFlags::None;
+            if (Thread::current()->block<Thread::WriteBlocker>({}, *description, unblock_flags).was_interrupted()) {
+                return EINTR;
+            }
+            // TODO: handle exceptions in unblock_flags
+        }
+
+        auto bytes_sent = TRY(socket.sendto(*description, data_buffer, iovs[0].iov_len, flags, user_addr, addr_length));
+        if (bytes_sent > 0)
+            return bytes_sent;
+    }
 }
 
 ErrorOr<FlatPtr> Process::sys$recvmsg(int sockfd, Userspace<struct msghdr*> user_msg, int flags)