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blockdev: make image streaming safe across hotplug 

Unplugging a storage interface like virtio-blk causes the host block
device to be deleted too.  Long-running operations like block migration
must take a DriveInfo reference to prevent the BlockDriverState from
being freed.  For image streaming we can do the same thing.

Note that it is not possible to acquire/release the drive reference in
block.c where the block job functions live because
drive_get_ref()/drive_put_ref() are blockdev.c functions.  Calling them
from block.c would be a layering violation - tools like qemu-img don't
even link against blockdev.c.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2012-01-18 14:40:50 +00:00 committed by Kevin Wolf
parent fb5458cd10
commit aa398a5c3a
1 changed files with 38 additions and 0 deletions
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38
blockdev.c
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@ -202,6 +202,37 @@ void drive_get_ref(DriveInfo *dinfo)
dinfo->refcount++;
}
typedef struct {
QEMUBH *bh;
DriveInfo *dinfo;
} DrivePutRefBH;
static void drive_put_ref_bh(void *opaque)
{
DrivePutRefBH *s = opaque;
drive_put_ref(s->dinfo);
qemu_bh_delete(s->bh);
g_free(s);
}
/*
* Release a drive reference in a BH
*
* It is not possible to use drive_put_ref() from a callback function when the
* callers still need the drive. In such cases we schedule a BH to release the
* reference.
*/
static void drive_put_ref_bh_schedule(DriveInfo *dinfo)
{
DrivePutRefBH *s;
s = g_new(DrivePutRefBH, 1);
s->bh = qemu_bh_new(drive_put_ref_bh, s);
s->dinfo = dinfo;
qemu_bh_schedule(s->bh);
}
static int parse_block_error_action(const char *buf, int is_read)
{
if (!strcmp(buf, "ignore")) {
@ -934,6 +965,8 @@ static void block_stream_cb(void *opaque, int ret)
monitor_protocol_event(QEVENT_BLOCK_JOB_COMPLETED, obj);
}
qobject_decref(obj);
drive_put_ref_bh_schedule(drive_get_by_blockdev(bs));
}
void qmp_block_stream(const char *device, bool has_base,
@ -966,6 +999,11 @@ void qmp_block_stream(const char *device, bool has_base,
}
}
/* Grab a reference so hotplug does not delete the BlockDriverState from
* underneath us.
*/
drive_get_ref(drive_get_by_blockdev(bs));
trace_qmp_block_stream(bs, bs->job);
}