Handle G_IO_HUP in tcp_chr_read for tcp chardev

Since commit cdaa86a5
("Add G_IO_HUP handler for socket chardev")
GLib limitation results in a bug on Windows host. Steps to reproduce:

Start qemu: qemu-system-i386 -qmp tcp:127.0.0.1:4444:server:nowait
Connect with telnet: telnet 127.0.0.1 4444
Try sending some data from telnet.
Expected result: answers from QEMU.
Observed result: no answers (actually tcp_chr_read is not called at all).

Due to GLib limitations it is not possible to create several watches on one
channel on Windows hosts. See bug #338943 in GNOME bugzilla for details:
https://bugzilla.gnome.org/show_bug.cgi?id=338943

This reimplements commit cdaa86a5
("Add G_IO_HUP handler for socket chardev") using a single watch:

Handle G_IO_HUP in tcp_chr_read instead. It is already watched by a
corresponding watch.  Remove the second watch with its handler.

Cc: Antonios Motakis <a.motakis@virtualopensystems.com>
Cc: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: NKirill Batuzov <batuzovk@ispras.ru>
Signed-off-by: NNikita Belov <zodiac@ispras.ru>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

include/sysemu/char.h

@@ -84,7 +84,6 @@ struct CharDriverState {
     int avail_connections;
     int is_mux;
     guint fd_in_tag;
-    guint fd_hup_tag;
     QemuOpts *opts;
     QTAILQ_ENTRY(CharDriverState) next;
 };

qemu-char.c

@@ -2673,6 +2673,12 @@ static gboolean tcp_chr_read(GIOChannel *chan, GIOCondition cond, void *opaque)
     uint8_t buf[READ_BUF_LEN];
     int len, size;
 
+    if (cond & G_IO_HUP) {
+        /* connection closed */
+        tcp_chr_disconnect(chr);
+        return TRUE;
+    }
+
     if (!s->connected || s->max_size <= 0) {
         return TRUE;
     }
@@ -2724,25 +2730,6 @@ CharDriverState *qemu_chr_open_eventfd(int eventfd)
 }
 #endif
 
-static gboolean tcp_chr_chan_close(GIOChannel *channel, GIOCondition cond,
-                                   void *opaque)
-{
-    CharDriverState *chr = opaque;
-
-    if (cond != G_IO_HUP) {
-        return FALSE;
-    }
-
-    /* connection closed */
-    tcp_chr_disconnect(chr);
-    if (chr->fd_hup_tag) {
-        g_source_remove(chr->fd_hup_tag);
-        chr->fd_hup_tag = 0;
-    }
-
-    return TRUE;
-}
-
 static void tcp_chr_connect(void *opaque)
 {
     CharDriverState *chr = opaque;
@@ -2752,8 +2739,6 @@ static void tcp_chr_connect(void *opaque)
     if (s->chan) {
         chr->fd_in_tag = io_add_watch_poll(s->chan, tcp_chr_read_poll,
                                            tcp_chr_read, chr);
-        chr->fd_hup_tag = g_io_add_watch(s->chan, G_IO_HUP, tcp_chr_chan_close,
-                                         chr);
     }
     qemu_chr_be_generic_open(chr);
 }