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block: Introduce BlockDriver.bdrv_drain callback

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Drivers can have internal request sources that generate IO, like the
need_check_timer in QED. Since we want quiesced periods that contain
nested event loops in block layer, we need to have a way to disable such
event sources.

Block drivers must implement the "bdrv_drain" callback if it has any
internal sources that can generate I/O activity, like a timer or a
worker thread (even in a library) that can schedule QEMUBH in an
asynchronous callback.

Update the comments of bdrv_drain and bdrv_drained_begin accordingly.

Like bdrv_requests_pending(), we should consider all the children of bs.
Before, the while loop just works, as bdrv_requests_pending() already
tracks its children; now we mustn't miss the callback, so recurse down
explicitly.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1447064214-29930-9-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fam Zheng 2015-11-09 18:16:53 +08:00 committed by Kevin Wolf
parent 83c98d7b92
commit 67da1dc5ce
2 changed files with 21 additions and 1 deletions
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16
block/io.c
View file

@ -237,8 +237,21 @@ bool bdrv_requests_pending(BlockDriverState *bs)
return false;
}
static void bdrv_drain_recurse(BlockDriverState *bs)
{
BdrvChild *child;
if (bs->drv && bs->drv->bdrv_drain) {
bs->drv->bdrv_drain(bs);
}
QLIST_FOREACH(child, &bs->children, next) {
bdrv_drain_recurse(child->bs);
}
}
/*
* Wait for pending requests to complete on a single BlockDriverState subtree
* Wait for pending requests to complete on a single BlockDriverState subtree,
* and suspend block driver's internal I/O until next request arrives.
*
* Note that unlike bdrv_drain_all(), the caller must hold the BlockDriverState
* AioContext.
@ -251,6 +264,7 @@ void bdrv_drain(BlockDriverState *bs)
{
bool busy = true;
bdrv_drain_recurse(bs);
while (busy) {
/* Keep iterating */
bdrv_flush_io_queue(bs);

6
include/block/block_int.h
View file

@ -295,6 +295,12 @@ struct BlockDriver {
*/
int (*bdrv_probe_geometry)(BlockDriverState *bs, HDGeometry *geo);
/**
* Drain and stop any internal sources of requests in the driver, and
* remain so until next I/O callback (e.g. bdrv_co_writev) is called.
*/
void (*bdrv_drain)(BlockDriverState *bs);
QLIST_ENTRY(BlockDriver) list;
};