At 2015/6/22 20:39, Stefan Hajnoczi Wrote:
On Sat, Jun 20, 2015 at 11:31:52AM +0800, Wen Congyang wrote:
At 2015/6/19 18:49, Stefan Hajnoczi Wrote:
On Fri, Jun 19, 2015 at 08:54:56AM +0800, Wen Congyang wrote:
On 06/19/2015 12:06 AM, Stefan Hajnoczi wrote:
On Thu, Jun 18, 2015 at 10:36:39PM +0800, Wen Congyang wrote:
At 2015/6/18 20:55, Stefan Hajnoczi Wrote:
On Thu, Jun 18, 2015 at 04:49:12PM +0800, Wen Congyang wrote:
+void bdrv_connect(BlockDriverState *bs, Error **errp)
+{
+ BlockDriver *drv = bs->drv;
+
+ if (drv && drv->bdrv_connect) {
+ drv->bdrv_connect(bs, errp);
+ } else if (bs->file) {
+ bdrv_connect(bs->file, errp);
+ } else {
+ error_setg(errp, "this feature or command is not currently supported");
+ }
+}
+
+void bdrv_disconnect(BlockDriverState *bs)
+{
+ BlockDriver *drv = bs->drv;
+
+ if (drv && drv->bdrv_disconnect) {
+ drv->bdrv_disconnect(bs);
+ } else if (bs->file) {
+ bdrv_disconnect(bs->file);
+ }
+}
Please add doc comments describing the semantics of these commands.
Where should it be documented? In the header file?
block.h doesn't document prototypes in the header file, please document
the function definition in block.c. (QEMU is not consistent here, some
places do it the other way around.)
Why are these operations needed when there is already a bs->drv == NULL
case which means the BDS is not ready for read/write?
The purpos is that: don't connect to nbd server when opening a nbd client.
connect/disconnect
to nbd server when we need to do it.
IIUC, if bs->drv is NULL, it means that the driver is ejected? Here,
connect/disconnect
means that connect/disconnect to remote target(The target may be in another
host).
Connect/disconnect puts something on the QEMU command-line that isn't
ready at startup time.
How about using monitor commands to add objects when needed instead?
That is cleaner because it doesn't introduce a new state (which is only
implemented for nbd).
The problem is that, nbd client is one child of quorum, and quorum must have
more
than one child. The nbd server is not ready until colo is running.
A monitor command to hot add/remove quorum children solves this problem
and could also be used in other scenarios (e.g. user decides to take a
quorum child offline).
For replication case, we always do checkpoint again and again after
migration. If the
disk is not synced before migration, we will use disk mirgation or mirror
job to sync
it. So we cannot start block replication when migration is running. We need
that nbd
client is not ready when migration is running, and it is ready between
migration ends
and checkpoint begins. Using a monotir command add the nbd client will cause
larger
downtime. So if the nbd client has been added(only not connect to the nbd
server),
we can connect to nbd server automatically.
I'm not sure I understand you. Can you rephrase this?
We only use block replication after migration because we assume that the
disk has been synced
before block replication is started, so we only forward new write
requests via nbd.
The NBD connect should not be performed during downtime, regardless of
whether a monitor command is used or not.
Why?
Thanks
Wen Congyang
Stefan
