Block hot unplug is racy since the guest is required to acknowlege the ACPI
unplug event; this may not happen synchronously with the device removal command
This series aims to close a gap where by mgmt applications that assume the
block resource has been removed without confirming that the guest has
acknowledged the removal may re-assign the underlying device to a second guest
leading to data leakage.
This series introduces a new montor command to decouple asynchornous device
removal from restricting guest access to a block device. We do this by creating
a new monitor command drive_unplug which maps to a bdrv_unplug() command which
does a qemu_aio_flush; bdrv_flush() and bdrv_close(). Once complete, subsequent
IO is rejected from the device and the guest will get IO errors but continue to
function.
A subsequent device removal command can be issued to remove the device, to which
the guest may or maynot respond, but as long as the unplugged bit is set, no IO
will be sumbitted.
Changes since v1:
- Added qemu_aio_flush() before bdrv_flush() to wait on pending io
Signed-off-by: Ryan Harper<address@hidden>
---
block.c | 7 +++++++
block.h | 1 +
blockdev.c | 26 ++++++++++++++++++++++++++
blockdev.h | 1 +
hmp-commands.hx | 15 +++++++++++++++
5 files changed, 50 insertions(+), 0 deletions(-)
diff --git a/block.c b/block.c
index a19374d..be47655 100644
--- a/block.c
+++ b/block.c
@@ -1328,6 +1328,13 @@ void bdrv_set_removable(BlockDriverState *bs, int
removable)
}
}
+void bdrv_unplug(BlockDriverState *bs)
+{
+ qemu_aio_flush();
+ bdrv_flush(bs);
+ bdrv_close(bs);
+}