chardev: add some comments about the class methods

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210804154848.557328-5-marcandre.lureau@redhat.com>

include/chardev/char.h

@@ -254,24 +254,57 @@ struct ChardevClass {
 
     bool internal; /* TODO: eventually use TYPE_USER_CREATABLE */
     bool supports_yank;
+
+    /* parse command line options and populate QAPI @backend */
     void (*parse)(QemuOpts *opts, ChardevBackend *backend, Error **errp);
 
+    /* called after construction, open/starts the backend */
     void (*open)(Chardev *chr, ChardevBackend *backend,
                  bool *be_opened, Error **errp);
 
+    /* write buf to the backend */
     int (*chr_write)(Chardev *s, const uint8_t *buf, int len);
+
+    /*
+     * Read from the backend (blocking). A typical front-end will instead rely
+     * on chr_can_read/chr_read being called when polling/looping.
+     */
     int (*chr_sync_read)(Chardev *s, const uint8_t *buf, int len);
+
+    /* create a watch on the backend */
     GSource *(*chr_add_watch)(Chardev *s, GIOCondition cond);
+
+    /* update the backend internal sources */
     void (*chr_update_read_handler)(Chardev *s);
+
+    /* send an ioctl to the backend */
     int (*chr_ioctl)(Chardev *s, int cmd, void *arg);
+
+    /* get ancillary-received fds during last read */
     int (*get_msgfds)(Chardev *s, int* fds, int num);
+
+    /* set ancillary fds to be sent with next write */
     int (*set_msgfds)(Chardev *s, int *fds, int num);
+
+    /* accept the given fd */
     int (*chr_add_client)(Chardev *chr, int fd);
+
+    /* wait for a connection */
     int (*chr_wait_connected)(Chardev *chr, Error **errp);
+
+    /* disconnect a connection */
     void (*chr_disconnect)(Chardev *chr);
+
+    /* called by frontend when it can read */
     void (*chr_accept_input)(Chardev *chr);
+
+    /* set terminal echo */
     void (*chr_set_echo)(Chardev *chr, bool echo);
+
+    /* notify the backend of frontend open state */
     void (*chr_set_fe_open)(Chardev *chr, int fe_open);
+
+    /* handle various events */
     void (*chr_be_event)(Chardev *s, QEMUChrEvent event);
 };