Christian Brauner
fe18d94610
A follow-up to the AddStorage / RemoveStorage series. ReplaceStorage
swaps the *backing file* of an already-attached storage device on a
running vmspawn-managed VM, leaving the guest-visible device frontend
(virtio-blk, virtio-scsi, nvme, scsi-cd) and every other property of
the device untouched. The intended use is to point an existing disk
at a new image without the guest seeing a hot-unplug/hot-plug cycle.
The signature mirrors AddStorage minus the 'config' field: the
device frontend doesn't change, only the backing behind it. Read-
only / read-write is derived from the new fd's O_ACCMODE; scsi-cd is
forced read-only to match the boot-time policy. S_ISBLK on the new
fd selects host_device vs file driver, matching AddStorage.
The QMP primitive is blockdev-reopen. It cannot change a file /
host_device node's 'filename' so we can't just point the existing
file node at a new fd, but it can swap a format node's 'file' child
to a different existing monitor-owned node by node-name reference
(case 3 in qemu/qapi/block-core.json:5034-5040). The chain is:
add-fd (host fd → new fdset)
blockdev-add (new file node, filename=/dev/fdset/N — fd-only)
remove-fd (release monitor's ref; new file holds the dup)
blockdev-reopen (format node, file = new file node-name)
blockdev-del (old file node; its dup release frees old fdset)
The reopen options must restate every option the original blockdev-
add emitted on the format node — blockdev-reopen resets any
unspecified option to its driver default. The 'file' field is a
node-name string reference, never a path.
No new errors and no new IDL types beyond the method itself;
everything is built on the existing NoSuchStorage / StorageImmutable
/ NotConnected / EBUSY vocabulary.
The series is:
vmspawn: split blockdev-add into separate file and format calls
Preparatory refactor. qemu/blockdev.c:3440 only marks the
top-level BDS returned by blockdev-add as monitor-owned;
inline children are NOT, so blockdev-del later rejects them
with "Node X is not owned by the monitor". Split into two
blockdev-add calls so the file node is independently
deletable. DriveInfo gains qmp_file_node_name and a
file_generation counter; the teardown helper deletes format
then file (file-first is rejected as "node used as 'file'
of Y"). The ephemeral path was already structured this way;
only the regular add path changes. Drops the now-unused
qmp_build_blockdev_add_inline().
shared/varlink-io.systemd.MachineInstance: add ReplaceStorage method
IDL only: ReplaceStorage(fileDescriptorIndex, name). No new
errors.
vmspawn: implement io.systemd.MachineInstance.ReplaceStorage
vmspawn_qmp_replace_block_device() entry point, ReplaceCtx
(refcounted, ReplaceCtxStateFlags for partial-state tracking)
and four async callbacks plus an idempotent replace_fail.
file_generation is bumped before issuing blockdev-add so
retries don't collide on node-name.
BLOCK_DEVICE_STATE_REPLACE_PENDING gates concurrent
Replace / Remove on the same drive. On reopen success the
trailing blockdev-del of the old file node fires from the
reopen callback; its failure logs a warning and still replies
success (the swap already committed; the orphan resolves at VM
exit). QMP disconnect mid-replace routes via
qmp_client_fail_pending → replace_fail → NotConnected.
test: integration test for io.systemd.MachineInstance.ReplaceStorage
TEST-87-AUX-UTILS-VM.replace-storage covers happy-path replace,
successive replaces (file_generation rotation), StorageImmutable
rejection on the boot-time drive, NoSuchStorage on unknown
names, InvalidParameter on malformed names, and clean
RemoveStorage after a replace (proves the new file node is
monitor-owned and the teardown order works). Backing files are
passed via 'varlinkctl --push-fd'; no machinectl front-end is
added in this round.
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
System and Service Manager
Details
Most documentation is available on systemd's web site.
Assorted, older, general information about systemd can be found in the systemd Wiki.
Information about build requirements is provided in the README file.
Consult our NEWS file for information about what's new in the most recent systemd versions.
Please see the Code Map for information about this repository's layout and content.
Please see the Hacking guide for information on how to hack on systemd and test your modifications.
Please see our Contribution Guidelines for more information about filing GitHub Issues and posting GitHub Pull Requests.
When preparing patches for systemd, please follow our Coding Style Guidelines.
If you are looking for support, please contact our mailing list, join our IRC channel #systemd on libera.chat or Matrix channel
Stable branches with backported patches are available in the stable repo.
We have a security bug bounty program sponsored by the Sovereign Tech Fund hosted on YesWeHack
Repositories with distribution packages built from git main are available on OBS, and also repositories with packages built from the latest stable release