char: add a QEMU_CHAR_FEATURE_GCONTEXT flag

QEMU_CHAR_FEATURE_GCONTEXT declares the character device can switch
GMainContext.

Assert we don't switch context when the character device doesn't
provide this feature.  Character device users must not violate this
restriction.  In particular, user configurations that violate them
must be rejected.

Existing frontend that rely on context switching would now assert() if
the backend doesn't allow it (instead of silently producing undesired
events in the default context). Following patches improve the
situation by reporting an error earlier instead, on the frontend side.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20181205203737.9011-4-marcandre.lureau@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

diff --git a/chardev/char.c b/chardev/char.c
index 152dde5327d7291a2efe1916f9891b2962db060c..ccba36bafb5f0d6fe8306886ad4af30523118e37 100644 (file)
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -193,6 +193,8 @@ void qemu_chr_be_update_read_handlers(Chardev *s,
 {
     ChardevClass *cc = CHARDEV_GET_CLASS(s);
 
+    assert(qemu_chr_has_feature(s, QEMU_CHAR_FEATURE_GCONTEXT)
+           || !context);
     s->gcontext = context;
     if (cc->chr_update_read_handler) {
         cc->chr_update_read_handler(s);
@@ -240,6 +242,15 @@ static void char_init(Object *obj)
 
     chr->logfd = -1;
     qemu_mutex_init(&chr->chr_write_lock);
+
+    /*
+     * Assume if chr_update_read_handler is implemented it will
+     * take the updated gcontext into account.
+     */
+    if (CHARDEV_GET_CLASS(chr)->chr_update_read_handler) {
+        qemu_chr_set_feature(chr, QEMU_CHAR_FEATURE_GCONTEXT);
+    }
+
 }
 
 static int null_chr_write(Chardev *chr, const uint8_t *buf, int len)

diff --git a/include/chardev/char.h b/include/chardev/char.h
index 7becd8c80c820f7f8ff9d03c2f02c882daa8361b..014566c3defa9443f87c6c289172351fb51b6412 100644 (file)
--- a/include/chardev/char.h
+++ b/include/chardev/char.h
@@ -47,6 +47,9 @@ typedef enum {
     QEMU_CHAR_FEATURE_FD_PASS,
     /* Whether replay or record mode is enabled */
     QEMU_CHAR_FEATURE_REPLAY,
+    /* Whether the gcontext can be changed after calling
+     * qemu_chr_be_update_read_handlers() */
+    QEMU_CHAR_FEATURE_GCONTEXT,
 
     QEMU_CHAR_FEATURE_LAST,
 } ChardevFeature;