kernel: Add POLLHUP and store it when a polled socket's peer disconnects

kernel/src/net/Socket.h

@@ -69,6 +69,8 @@ class Socket : public VFS::FileInode
 
     virtual bool can_read_data() const = 0;
 
+    virtual bool peer_disconnected() const = 0;
+
     virtual ~Socket() = default;
 
   protected:

kernel/src/net/UnixSocket.h

@@ -27,6 +27,11 @@ class UnixSocket : public Socket
         return !m_listen_queue.is_empty();
     }
 
+    bool peer_disconnected() const override
+    {
+        return m_state == Reset;
+    }
+
     Result<usize> send(const u8*, usize, int) override;
     Result<usize> recv(u8*, usize, int) const override;
 

kernel/src/sys/poll.cpp

@@ -50,6 +50,9 @@ Result<u64> sys_poll(Registers*, SyscallArgs args)
 
             if (kfds[i].events & POLLIN)
             {
+                fds_with_events++;
+                kfds[i].revents |= POLLIN;
+
                 if (inode->type() == VFS::InodeType::Socket)
                 {
                     auto socket = (Socket*)inode.ptr();
@@ -58,6 +61,11 @@ Result<u64> sys_poll(Registers*, SyscallArgs args)
                         fds_with_events++;
                         kfds[i].revents |= POLLIN;
                     }
+                    if (socket->peer_disconnected())
+                    {
+                        fds_with_events++;
+                        kfds[i].revents |= POLLHUP;
+                    }
                 }
                 else
                 {

libc/include/bits/poll.h

@@ -8,6 +8,7 @@
 #define POLLIN (1 << 0)
 #define POLLERR (1 << 1)
 #define POLLNVAL (1 << 2)
+#define POLLHUP (1 << 3)
 
 typedef __u64_t nfds_t;