char: Add framework for a 'write unblocked' callback

The char layer can let users know that the driver will block on further
input.  For users interested in not blocking, they can assign a function
pointer that will be called back when the driver becomes writable.  This
patch just adds the function pointers to the CharDriverState structure,
future patches will enable the nonblocking and callback functionality.

Signed-off-by: Amit Shah <amit.shah@redhat.com>

2 files changed, 8 insertions, 0 deletions

diff --git a/qemu-char.c b/qemu-char.c
index 3a31d8b0a..ce7641142 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -206,11 +206,14 @@ void qemu_chr_add_handlers(CharDriverState *s,
     }
     s->chr_can_read = handlers->fd_can_read;
     s->chr_read = handlers->fd_read;
+    s->chr_write_unblocked = handlers->fd_write_unblocked;
     s->chr_event = handlers->fd_event;
     s->handler_opaque = opaque;
     if (s->chr_update_read_handler)
         s->chr_update_read_handler(s);
 
+    s->write_blocked = false;
+
     /* We're connecting to an already opened device, so let's make sure we
        also get the open event */
     if (s->opened) {
diff --git a/qemu-char.h b/qemu-char.h
index 185377c2f..bf06da012 100644
--- a/qemu-char.h
+++ b/qemu-char.h
@@ -61,6 +61,9 @@ struct CharDriverState {
     IOEventHandler *chr_event;
     IOCanReadHandler *chr_can_read;
     IOReadHandler *chr_read;
+    IOHandler *chr_write_unblocked;
+    void (*chr_enable_write_fd_handler)(struct CharDriverState *chr);
+    void (*chr_disable_write_fd_handler)(struct CharDriverState *chr);
     void *handler_opaque;
     void (*chr_send_event)(struct CharDriverState *chr, int event);
     void (*chr_close)(struct CharDriverState *chr);
@@ -71,6 +74,8 @@ struct CharDriverState {
     char *label;
     char *filename;
     int opened;
+    /* Are we in a blocked state? */
+    bool write_blocked;
     QTAILQ_ENTRY(CharDriverState) next;
 };