Re: [Qemu-devel] [PATCH] block/rbd: add .bdrv_reopen_prepare() stub

["Sebastian Färber" <sfaerber82@gmail.com>]

Hi Kevin,

> A correct reopen implementation must consider all options and flags that
> .bdrv_open() looked at.
> 
> The options are okay, as both "filename" and "password-secret" aren't
> things that we want to allow a reopen to change. However, in the flags
> BDRV_O_NOCACHE makes a difference:
> 
>     if (flags & BDRV_O_NOCACHE) {
>         rados_conf_set(s->cluster, "rbd_cache", "false");
>     } else {
>         rados_conf_set(s->cluster, "rbd_cache", "true");
>     }
> 
> A reopen must either update the setting, or if it can't (e.g. because
> librbd doesn't support it) any attempt to change the flag must fail.

Thanks for the feedback.
As far as i can tell it's not possible to update the cache settings
without reconnecting. I've added a check in the following patch.
Would be great if someone who knows the internals of ceph/rbd could
have a look as well.

Sebastian

-- >8 --
Subject: [PATCH] block/rbd: add .bdrv_reopen_prepare() stub

Add support for reopen() by adding the .bdrv_reopen_prepare() stub

Signed-off-by: Sebastian Färber <sfaerber82@gmail.com>
---
 block/rbd.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/block/rbd.c b/block/rbd.c
index 5bc5b32..8ecf096 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -577,6 +577,19 @@ failed_opts:
     return r;
 }

+/* Note that this will not re-establish a connection with the Ceph cluster
+   - it is effectively a NOP.  */
+static int qemu_rbd_reopen_prepare(BDRVReopenState *state,
+                                   BlockReopenQueue *queue, Error **errp)
+{
+    if (state->flags & BDRV_O_NOCACHE &&
+        ((state->bs->open_flags & BDRV_O_NOCACHE) == 0)) {
+        error_setg(errp, "Cannot turn off rbd_cache during reopen");
+        return -EINVAL;
+    }
+    return 0;
+}
+
 static void qemu_rbd_close(BlockDriverState *bs)
 {
     BDRVRBDState *s = bs->opaque;
@@ -976,6 +989,7 @@ static BlockDriver bdrv_rbd = {
     .instance_size      = sizeof(BDRVRBDState),
     .bdrv_needs_filename = true,
     .bdrv_file_open     = qemu_rbd_open,
+    .bdrv_reopen_prepare = qemu_rbd_reopen_prepare,
     .bdrv_close         = qemu_rbd_close,
     .bdrv_create        = qemu_rbd_create,
     .bdrv_has_zero_init = bdrv_has_zero_init_1,
--
1.8.3.1