9pfs: split out fs driver core of v9fs_co_readdir()

The implementation of v9fs_co_readdir() has two parts: the outer
part is executed by main I/O thread, whereas the inner part is
executed by fs driver on a background I/O thread.

Move the inner part to its own new, private function do_readdir(),
so it can be shared by another upcoming new function.

This is just a preparatory patch for the subsequent patch, with the
purpose to avoid the next patch to clutter the overall diff.

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <a426ee06e77584fa2d8253ce5d8bea519eb3ffd4.1596012787.git.qemu_oss@crudebyte.com>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>

hw/9pfs/codir.c

@@ -18,28 +18,38 @@
 #include "qemu/main-loop.h"
 #include "coth.h"
 
+/*
+ * Intended to be called from bottom-half (e.g. background I/O thread)
+ * context.
+ */
+static int do_readdir(V9fsPDU *pdu, V9fsFidState *fidp, struct dirent **dent)
+{
+    int err = 0;
+    V9fsState *s = pdu->s;
+    struct dirent *entry;
+
+    errno = 0;
+    entry = s->ops->readdir(&s->ctx, &fidp->fs);
+    if (!entry && errno) {
+        *dent = NULL;
+        err = -errno;
+    } else {
+        *dent = entry;
+    }
+    return err;
+}
+
 int coroutine_fn v9fs_co_readdir(V9fsPDU *pdu, V9fsFidState *fidp,
                                  struct dirent **dent)
 {
     int err;
-    V9fsState *s = pdu->s;
 
     if (v9fs_request_cancelled(pdu)) {
         return -EINTR;
     }
-    v9fs_co_run_in_worker(
-        {
-            struct dirent *entry;
-
-            errno = 0;
-            entry = s->ops->readdir(&s->ctx, &fidp->fs);
-            if (!entry && errno) {
-                err = -errno;
-            } else {
-                *dent = entry;
-                err = 0;
-            }
-        });
+    v9fs_co_run_in_worker({
+        err = do_readdir(pdu, fidp, dent);
+    });
     return err;
 }