Commit 67da1dc5 authored by Fam Zheng's avatar Fam Zheng Committed by Kevin Wolf
Browse files

block: Introduce BlockDriver.bdrv_drain callback 



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: default avatarFam Zheng <famz@redhat.com>
Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Message-id: 1447064214-29930-9-git-send-email-famz@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent 83c98d7b

block/io.c

+15 −1
Original line number Diff line number Diff line
@@ -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);

include/block/block_int.h

+6 −0
Original line number Diff line number Diff line
@@ -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;

};