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From: | Josh Durgin |
Subject: | Re: [Qemu-block] [PATCH] block/rbd: add .bdrv_reopen_prepare() stub |
Date: | Tue, 17 May 2016 11:48:15 -0700 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1 |
On 05/17/2016 03:03 AM, Sebastian Färber wrote:
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.
Updating this setting on an open image won't do anything, but if you rbd_close() and rbd_open() it again the setting will take effect. rbd_close() will force a flush of any pending I/O in librbd and free the memory for librbd's ImageCtx, which may or may not be desired here.
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.
There's no need to reset the librados state, so connections to the cluster can stick around. I'm a bit unclear on the bdrv_reopen_* functions though - what is their intended use and semantics?
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 <address@hidden> --- 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
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