aboutsummaryrefslogtreecommitdiff
path: root/blockdev-nbd.c
diff options
context:
space:
mode:
authorEric Blake <eblake@redhat.com>2019-01-11 13:47:17 -0600
committerEric Blake <eblake@redhat.com>2019-01-14 10:09:46 -0600
commit5fcbeb06812685a2c6d7e0e6f28f018987d08b79 (patch)
tree3689660507f2713004aacdba7cc1f288aa798ac5 /blockdev-nbd.c
parent3fa4c76590569f9dc128beb3eee65aaefcb6321e (diff)
nbd: Allow bitmap export during QMP nbd-server-add
With the experimental x-nbd-server-add-bitmap command, there was a window of time where an NBD client could see the export but not the associated dirty bitmap, which can cause a client that planned on using the dirty bitmap to be forced to treat the entire image as dirty as a safety fallback. Furthermore, if the QMP client successfully exports a disk but then fails to add the bitmap, it has to take on the burden of removing the export. Since we don't allow changing the exposed dirty bitmap (whether to a different bitmap, or removing advertisement of the bitmap), it is nicer to make the bitmap tied to the export at the time the export is created, with automatic failure to export if the bitmap is not available. The experimental command included an optional 'bitmap-export-name' field for remapping the name exposed over NBD to be different from the bitmap name stored on disk. However, my libvirt demo code for implementing differential backups on top of persistent bitmaps did not need to take advantage of that feature (it is instead possible to create a new temporary bitmap with the desired name, use block-dirty-bitmap-merge to merge one or more persistent bitmaps into the temporary, then associate the temporary with the NBD export, if control is needed over the exported bitmap name). Hence, I'm not copying that part of the experiment over to the stable addition. For more details on the libvirt demo, see https://www.redhat.com/archives/libvir-list/2018-October/msg01254.html, https://kvmforum2018.sched.com/event/FzuB/facilitating-incremental-backup-eric-blake-red-hat This patch focuses on the user interface, and reduces (but does not completely eliminate) the window where an NBD client can see the export but not the dirty bitmap, with less work to clean up after errors. Later patches will add further cleanups now that this interface is declared stable via a single QMP command, including removing the race window. Update test 223 to use the new interface. Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20190111194720.15671-6-eblake@redhat.com>
Diffstat (limited to 'blockdev-nbd.c')
-rw-r--r--blockdev-nbd.c12
1 files changed, 11 insertions, 1 deletions
diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 582ffded77..ec8cf0ab8c 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -140,7 +140,8 @@ void qmp_nbd_server_start(SocketAddressLegacy *addr,
}
void qmp_nbd_server_add(const char *device, bool has_name, const char *name,
- bool has_writable, bool writable, Error **errp)
+ bool has_writable, bool writable,
+ bool has_bitmap, const char *bitmap, Error **errp)
{
BlockDriverState *bs = NULL;
BlockBackend *on_eject_blk;
@@ -185,6 +186,15 @@ void qmp_nbd_server_add(const char *device, bool has_name, const char *name,
* our only way of accessing it is through nbd_export_find(), so we can drop
* the strong reference that is @exp. */
nbd_export_put(exp);
+
+ if (has_bitmap) {
+ Error *err = NULL;
+ nbd_export_bitmap(exp, bitmap, bitmap, &err);
+ if (err) {
+ error_propagate(errp, err);
+ nbd_export_remove(exp, NBD_SERVER_REMOVE_MODE_HARD, NULL);
+ }
+ }
}
void qmp_nbd_server_remove(const char *name,