char: introduce CharBackend

This new structure is meant to keep the details associated with a char
driver usage. On initialization, it gets a tag from the mux backend.
It can change its handlers thanks to qemu_chr_fe_set_handlers().

This structure is introduced so that all frontend will be moved to hold
and use a CharBackend. This will allow to better track char usage and
allocation, and help prevent some memory leaks or corruption.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20161022095318.17775-10-marcandre.lureau@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

include/sysemu/char.h

@@ -72,6 +72,12 @@ typedef enum {
     QEMU_CHAR_FEATURE_LAST,
 } CharDriverFeature;
 
+/* This is the backend as seen by frontend, the actual backend is
+ * CharDriverState */
+typedef struct CharBackend {
+    CharDriverState *chr;
+    int tag;
+} CharBackend;
 
 struct CharDriverState {
     QemuMutex chr_write_lock;
@@ -156,6 +162,8 @@ void qemu_chr_parse_common(QemuOpts *opts, ChardevCommon *backend);
  * Returns: a new character backend
  */
 CharDriverState *qemu_chr_new(const char *label, const char *filename);
+
+
 /**
  * @qemu_chr_disconnect:
  *
@@ -425,6 +433,48 @@ void qemu_chr_be_write_impl(CharDriverState *s, uint8_t *buf, int len);
  */
 void qemu_chr_be_event(CharDriverState *s, int event);
 
+/**
+ * @qemu_chr_fe_init:
+ *
+ * Initializes a front end for the given CharBackend and CharDriver.
+ *
+ * Returns: false on error.
+ */
+bool qemu_chr_fe_init(CharBackend *b, CharDriverState *s, Error **errp);
+
+/**
+ * @qemu_chr_fe_get_driver:
+ *
+ * Returns the driver associated with a CharBackend or NULL.
+ */
+CharDriverState *qemu_chr_fe_get_driver(CharBackend *be);
+
+/**
+ * @qemu_chr_fe_set_handlers:
+ * @b: a CharBackend
+ * @fd_can_read: callback to get the amount of data the frontend may
+ *               receive
+ * @fd_read: callback to receive data from char
+ * @fd_event: event callback
+ * @opaque: an opaque pointer for the callbacks
+ * @context: a main loop context or NULL for the default
+ *
+ * Set the front end char handlers.
+ */
+void qemu_chr_fe_set_handlers(CharBackend *b,
+                              IOCanReadHandler *fd_can_read,
+                              IOReadHandler *fd_read,
+                              IOEventHandler *fd_event,
+                              void *opaque,
+                              GMainContext *context);
+
+/**
+ * @qemu_chr_fe_take_focus:
+ *
+ * Take the focus (if the front end is muxed)
+ */
+void qemu_chr_fe_take_focus(CharBackend *b);
+
 void qemu_chr_add_handlers(CharDriverState *s,
                            IOCanReadHandler *fd_can_read,
                            IOReadHandler *fd_read,

qemu-char.c

@@ -910,6 +910,53 @@ static CharDriverState *qemu_chr_open_mux(const char *id,
     return chr;
 }
 
+CharDriverState *qemu_chr_fe_get_driver(CharBackend *be)
+{
+    return be->chr;
+}
+
+bool qemu_chr_fe_init(CharBackend *b, CharDriverState *s, Error **errp)
+{
+    int tag = 0;
+
+    if (s->is_mux) {
+        tag = mux_chr_new_handler_tag(s, errp);
+        if (tag < 0) {
+            return false;
+        }
+    }
+
+    b->tag = tag;
+    b->chr = s;
+
+    return true;
+}
+
+void qemu_chr_fe_set_handlers(CharBackend *b,
+                              IOCanReadHandler *fd_can_read,
+                              IOReadHandler *fd_read,
+                              IOEventHandler *fd_event,
+                              void *opaque,
+                              GMainContext *context)
+{
+    if (!b->chr) {
+        return;
+    }
+
+    qemu_chr_set_handlers(b->chr, fd_can_read, fd_read,
+                          fd_event, opaque, context, b->tag);
+
+    if (b->chr->is_mux) {
+        mux_chr_set_handlers(b->chr, context);
+    }
+}
+
+void qemu_chr_fe_take_focus(CharBackend *b)
+{
+    if (b->chr->is_mux) {
+        mux_set_focus(b->chr->opaque, b->tag);
+    }
+}
 
 typedef struct IOWatchPoll
 {
@@ -4184,6 +4231,9 @@ void qemu_chr_disconnect(CharDriverState *chr)
 
 static void qemu_chr_free_common(CharDriverState *chr)
 {
+    if (chr->be) {
+        chr->be->chr = NULL;
+    }
     g_free(chr->filename);
     g_free(chr->label);
     if (chr->logfd != -1) {