Virtio v1.2 says that if CONFIG_WCE is negotiated
but FLUSH is not, the device must initialize writeback to 0.
It also says that if CONFIG_WCE was not negotiated but FLUSH
was, the driver should assume presence of a writeback cache.
Introduce a pure is_writeback_enabled helper and a
set_writeback_mode helper. This makes the two call flows
explicit:
* write_config resolves the guest requested mode against the
negotiated features before storing it back
* activate starts from the default writeback preference and then
resolves it against the negotiated features
* reset restores the initial writeback state
This keeps the config space value and the runtime writeback flag
in sync and makes the spec driven fallback easier to follow.
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
PR #7852 fixed the missing VirtioBlockConfig fields but did not
change the feature advertisement logic. The condition
`sparse || disk_image.supports_zero_flag()` causes qcow2 to
advertise DISCARD even with sparse=false, because qcow2 can
mark clusters as zero (supports_zero_flag() returns true).
Windows viostor BSODs (DRIVER_IRQL_NOT_LESS_OR_EQUAL) when
DISCARD is advertised on qcow2 backends, making sparse=off
ineffective as a workaround for qcow2 images.
Restrict DISCARD to explicit sparse=true only. WRITE_ZEROES
remains available for all sparse-capable backends.
Fixes#7849
Signed-off-by: CMGS <ilskdw@gmail.com>
The sync fallback path in process_queue_submit() hardcoded
VIRTIO_BLK_S_IOERR for all errors. This caused unsupported
request errors to report IOERR to the guest instead of the
correct VIRTIO_BLK_S_UNSUPP.
Use ExecuteError::status() to return the appropriate status
code for each error variant.
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
Use logical_size() instead of physical_size() for the byte-range
advisory lock. physical_size() returns st_blocks*512 which is the
actual host allocation and can be smaller than the guest visible
extent on sparse files, leaving part of the range unprotected.
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
When configuring multiple queues for a virtio device, the guest can
activate between 1 and the configured amount of queues. The firmware,
for example, may activate only one queue, while a Linux guest would
likely activate all available queues.
The constructor of virtio-blk initializes the `paused_sync` barrier
using the configured queue count (plus one for the main thread). This
can be wrong if the guest enable a different number of queues at
activation time, which can make pause hang. Thus, we now recompute the
barrier size from the queues that are actually activated.
On-behalf-of: SAP sebastian.eydam@sap.com
Signed-off-by: Sebastian Eydam <sebastian.eydam@cyberus-technology.de>
Split the data length check into two conditions:
- reject descriptors shorter than one
virtio_blk_discard_write_zeroes segment, and
- reject payloads exceeding MAX_DISCARD_WRITE_ZEROES_SEG segments
Previously only the minimum length was checked and extra segments
were silently dropped.
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
Change Block to hold DiskBackend instead of
Box<dyn async_io::DiskFile>. In device_manager, existing formats
(raw, vhd, vhdx) are wrapped in DiskBackend::Legacy while
QcowDiskSync uses DiskBackend::Next. The fuzz target is updated
accordingly.
The Error::DiskResize variant now carries BlockError instead of
DiskFileError, matching the BlockResult return type of
DiskBackend::resize().
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
Set discard_sector_alignment from the logical block size
reported by the backend topology instead of hardcoding it
to 1 sector. This gives the guest accurate alignment hints
so it can avoid sub block discards that the filesystem
might silently ignore.
For example, on a 4K block filesystem the alignment is now
8 sectors (4096/512) instead of 1.
For image formats with their own allocation units (QCOW2
clusters, VHD/VHDX block sizes), the ideal alignment would
be derived from the format cluster/block size. This is
left for a followup that surfaces allocation granularity
through DiskTopology.
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
When VIRTIO_BLK_F_DISCARD or VIRTIO_BLK_F_WRITE_ZEROES features
are advertised, the virtio spec v1.2, sections 5.2.4 and
5.2.6.1, requires the corresponding VirtioBlockConfig fields
to contain valid, non zero values. Leaving them at zero causes
strictly behaved drivers to either reject the features or crash.
Populate max_discard_sectors, max_discard_seg,
discard_sector_alignment, max_write_zeroes_sectors,
max_write_zeroes_seg and write_zeroes_may_unmap after
feature advertisement so drivers can safely negotiate
these features.
Fixes: #7849
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
We ran the Microsoft Windows installer in CHV (via network + VNC) and
the installation always failed when the installer wanted to write the
partition table. Since recently, for very good reason, sector 0 writes
are disabled if the image type is not set explicitly and only
implicitly auto-detected as raw [0].
To ease troubleshooting, I've added a descriptive log message. It is a
little spammy, but it is what is required to help users to troubleshoot.
[0] 6ecdf90e22
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
Signal the guest before processing queue submissions to enable
earlier guest side completion event handling, reducing end-to-end
latency for block device operations.
FIO benchmarks show up to 7.4% bandwidth improvement at 16
iodepth and 4k block size with NVMe devices.
Signed-off-by: wuxinyue <wuxinyue.wxy@antgroup.com>
Add a per-disk lock_granularity parameter that lets users choose
between byte-range OFD locks and whole-file OFD locks:
--disk path=/foo.img,lock_granularity=byte-range
--disk path=/bar.img,lock_granularity=full
Byte-range is the default and matches QEMU behavior, working
best with storage backends where whole-file OFD locks are treated
as mandatory. The full option restores the original whole-file
locking for environments that depend on it.
The LockGranularityChoice enum and its FromStr impl live in the
block crate alongside the existing LockGranularity type. The
Block device converts the user-facing choice to the internal
LockGranularity at lock time, keeping device_manager.rs simple.
Closes: #7553
Signed-off-by: Victor Vieux <vieux@repl.it>
Rename the transport feature bit constant from
VIRTIO_F_IOMMU_PLATFORM to VIRTIO_F_ACCESS_PLATFORM across
the entire virtio-devices crate.
The virtio specification as of v1.1 carries bit 33 as
VIRTIO_F_ACCESS_PLATFORM. The Linux kernel UAPI header
<linux/virtio_config.h> carries VIRTIO_F_IOMMU_PLATFORM
only as a backward-compatible alias.
This is a pure rename with no functional or behavioral
change.
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
As well as rejecting writes to sector 0 in the case of raw files where
the user hasn't specified the image_type also reject virtio requests of
type discard and write_zeroes.
Signed-off-by: Rob Bradford <rbradford@meta.com>
If the disk image was autodetected to raw (not specified with image_type
= 0) then in the virtio-block subsystem generate errors for writes to
block 0 (treat as if read-only). This gives an immediate error vs using
the image implementations in the block subsystem.
Signed-off-by: Rob Bradford <rbradford@meta.com>
Unlike most virtio feature bits, VIRTIO_BLK_F_RO is not optional.
It indicates that the host is refusing to permit write operations, and
the guest must not be allowed to override it.
However, the block device currently does not enforce this. If the guest
does not negotiate VIRTIO_BLK_F_RO, the block device will think the
device is writable and forward write requests to the backend.
This is not a security problem right now because the backing device of a
read-only device is always opened read-only. The kernel will thus
reject the write operations with EBADF. If support is added for
receiving the backing device file descriptor via SCM_RIGHTS (#7704),
it will be possible to have a read-only block device backed by a
writable file descriptor. This would make the bug a genuine security
vulnerability.
Fix the bug by explicitly checking if VIRTIO_BLK_F_RO was offered but
not negotiated. In this case, log a warning and proceed as if the guest
did acknowledge the feature. This always indicates a guest driver bug.
Fixes: #7697
Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
OVMF sends FLUSH requests to read-only virtio-block devices. Refusing
these requests prevents OVMF from accessing the EFI System Partition and
therefore makes VMs unable to boot. Accept these requests instead.
them.
Ignoring these requests is possible, but inconsistent with fsync(2)
which honors them.
Fixes: #7698
Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
Add supports_zero_flag() to DiskFile trait to indicate whether a disk
format can mark clusters/blocks as reading zeros without deallocating
storage.
QCOW2 supports this via the zero flag in L2 entries. VHDX also has
PAYLOAD_BLOCK_ZERO state for this, though it's not yet implemented in
cloud-hypervisor.
This enables DISCARD to be advertised even with sparse=false for formats
with zero-flag support, since they can mark regions as zeros (keeps
storage allocated) instead of requiring full deallocation.
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
Add sparse boolean configuration option to DiskConfig with a default
value of true to control disk space allocation behavior.
When sparse is true, the disk uses sparse allocation where deallocated
blocks are returned to the filesystem, and the DISCARD feature is
advertised to the guest.
When sparse is false, disk space is kept fully allocated and DISCARD
is not advertised.
WRITE_ZEROES is always advertised when the backend supports it,
regardless of the sparse setting.
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
Add capability query to DiskFile trait to check backend
support for sparse operations (punch hole, write zeroes,
discard). Only advertise VIRTIO_BLK_F_DISCARD and
VIRTIO_BLK_F_WRITE_ZEROES when the backend supports these
operations.
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
This change is a prerequisite for live disk resizing. Before this
commit, the epoll-handler threads just got a copy of the sector
size which we cannot update during runtime.
On-behalf-of: SAP thomas.prescher@sap.com
Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>
https://github.com/cloud-hypervisor/cloud-hypervisor/pull/7294 adjusted
the checks for read-only requests made to virtio-blk devices and started
rejecting VIRTIO_BLK_T_GET_ID requests. These requests do not perform
any writes and are needed in order to access device serials from within
the guest.
Signed-off-by: Connor Brewster <cbrewster@hey.com>
This is a follow-up of [0].
# Advantages
- This saves dozens of unneeded clone()s across the whole code base
- Makes it much easier to reason about how parameters are used
(often we passed owned Arc/Rc versions without actually needing
ownership)
# Exceptions
For certain code paths, the alternatives would require awkward or overly
complex code, and in some cases the functions are the logical owners of
the values they take. In those cases, I've added
#[allow(clippy::needless_pass_by_value)].
This does not mean that one should not improve this in the future.
[0] 6a86c157af
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
This helps to uncover expensive and needless clones in the code base.
For example, I prevented extensive clones in the snapshot path where
(nested) BTreeMap's have been cloned over and over again. Further,
the lint helps devs to much better reason about the ownership of
parameters.
All of these changes have been done manually with the necessary
caution. A few structs that are cheap to clone are now `copy` so that
this lint won't trigger for them.
I didn't enable the lint so far as it is a massive rabbit hole and
needs much more fixes. Nevertheless, it is very useful.
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
The granularity has significant implications in typical cloud
deployments with network storage. The Linux kernel will sync advisory
locks to network file systems, but these backends may have different
policies and handle locks differently. For example, Netapp speaks a NFS
API but will treat advisory OFD locks for the whole file as mandatory
locks, whereas byte-range locks for the whole file will remain
advisory [0].
As it is a valid use case to prevent multiple CHV instances from
accessing the same disk but disk management software (e.g., Cinder in
OpenStack) should be able to snapshot disks while VMs are running, we
need special control over the lock granularity. Therefore, it is a valid
use case to lock the whole byte range of a disk image without
technically locking the whole file - to get the best of both worlds.
This also brings CHVs behavior in line with QEMU [1].
Whole-file locks remain a valid use case and could be supported later.
This patch only provides the necessary groundwork; making it
configurable is out of scope for now.
[0] https://kb.netapp.com/on-prem/ontap/da/NAS/NAS-KBs/How_is_Mandatory_Locking_supported_for_NFSv4_on_ONTAP_9
[1] <qemu>/util/osdep.c::qemu_lock_fcntl()
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
Consuming `&Arc<T>` as argument is almost always an antipattern as it
hides whether the callee is going to take over (shared) ownership
(by .clone()) or not. Instead, it is better to consume `&dyn T` or
`Arc<dyn T>` to be more explicit. This commit cleans up the code.
The change is very mechanic and was very easy to implement across the
code base.
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
Fix clippy warning `uninlined_format_args` reported by rustc rustc
1.89.0 (29483883e 2025-08-04).
```console
warning: variables can be used directly in the `format!` string
--> block/src/lib.rs:649:17
|
649 | info!("{} failed to create io_uring instance: {}", error_msg, e);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#uninlined_format_args
= note: `#[warn(clippy::uninlined_format_args)]` on by default
help: change this to
|
649 - info!("{} failed to create io_uring instance: {}", error_msg, e);
649 + info!("{error_msg} failed to create io_uring instance: {e}");
|
```
Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>
Cache and batch IO requests after parsing all
items in the queue, improving performance—especially
for small block sizes—by reducing per-request overhead.
Introduced two methods in the AsyncIo trait for batch
submission, with implementation in the raw disk backend.
This method should be called during/after parsing all block IO requests
in the available queue. If the batch submission is not enabled, by
default it does the old way of submitting requests.
Signed-off-by: Bo Chen <bchen@crusoe.ai>
Signed-off-by: Muminul Islam <muislam@microsoft.com>
Instead of returning boolean return an struct of completion status
so that it can be cached for batch submission.
Signed-off-by: Bo Chen <bchen@crusoe.ai>
Signed-off-by: Muminul Islam <muislam@microsoft.com>
This patch changes the read-only check using acked features bit, which
will help to check more features.
Signed-off-by: Songqian Li <sionli@tencent.com>
Instead of exiting on IO errors, report the errors to the guest with
VIRTIO_BLK_S_IOERR. For example, the guest kernel will log something
similar to this if the nbd behind /dev/vdc is unexpectedly disconnected:
[ 166.033957] I/O error, dev vdc, sector 264 op 0x1:(WRITE) flags 0x9800 phys_seg 1 prio class 2
[ 166.035083] Aborting journal on device vdc-8.
[ 166.037307] Buffer I/O error on dev vdc, logical block 9, lost sync page write
[ 166.038471] JBD2: I/O error when updating journal superblock for vdc-8.
[...]
[ 174.234470] EXT4-fs (vdc): I/O error while writing superblock
In case the rootfs is not located on the affected block device, this
will not crash the guest.
Fixes: #6995
Signed-off-by: Gauthier Jolly <contact@gjolly.fr>
This streamlines the code base to follow best practices for
error handling in Rust: Each error struct implements
std::error::Error (most due via thiserror::Error derive macro)
and sets its source accordingly.
This allows future work that nicely prints the error chains,
for example.
So far, the convention is that each error prints its
sub error as part of its Display::fmt() impl.
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
# What
This commit introduces file-based advisory locking for the files backing
up the block devices by using the fcntl() syscall with OFD locks. The
per-open-file-descriptor (OFD) locks are more robust than traditional
POSIX locks (F_SETLK) as they are not tied to process IDs and avoid
common issues in multithreaded or multi-fd scenarios [1]. Therefore,
we don't use `std::fs::File::try_lock()`, which is backed by F_SETLKW.
The locking mechanism is aware of the `readonly` property and allows
`n` readers or `1` writer (exclusive mode).
As the locks are advisory, multiple cloud-hypervisor processes can
prevent themselves from writing to the same file. However, this is not
a system-wide file-system level locking mechanism preventing to open()
a file.
The introduced new locking mechanism does not cover vhost-user devices.
# Why
To prevent misconfiguration and improve safety, it is good practice to
protect disk image files with a locking mechanism. Experience and common
best practices suggest that advisory locks are preferable over mandatory
locks due to better compatibility and fewer pitfalls (in fs space).
The introduced functionality is aligned with the approach taken by
QEMU [0], and is also recommended in [1].
# Implementation Details
We need to ensure that not only normal operation keeps working but also
state save/resume and live-migration. Especially for live migration,
it is crucial that the sender VMM releases the locks when the VM stops
so the receiver VMM can acquire them right after that.
Therefore, the locking and releasing happen directly on the block
device struct. The device manager knows all block devices and can
forward requests to these types.
Last but not least, this commit uses on explicit lock acquiring
but implicit lock releasing (FD close). It only explicitly releases
the locks where this integrates more smoothly into the existing
code.
# Testing
I tested
- normal operation
- state save/resume,
- device hot plugging,
- and live-migration
with read/shared and write/exclusive locks.
One can use the `fcntl-tool` to test if locks are actually acquired
or released [2].
# Links
[0] 825b96dbce/util/osdep.c (L266)
[1] https://apenwarr.ca/log/20101213
[2] https://crates.io/crates/fcntl-tool
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
Rust has a new way of constructing other error and clippy complains if
we are still using the older way to construct error message. Thus,
migrate to the new approach suggested by the clippy.
Warning from beta compiler:
error: this can be `std::io::Error::other(_)`
--> block/src/vhdx/mod.rs:142:17
|
| / std::io::Error::new(
| | std::io::ErrorKind::Other,
| | format!("Failed to update VHDx header: {e}"),
| | )
| |_________________^
|
= help: for further information visit
https://rust-lang.github.io/rust-clippy/master/index.html#io_other_error
help: use `std::io::Error::other`
std::io::Error::other(
format!("Failed to update VHDx header: {e}"),
Signed-off-by: Jinank Jain <jinankjain@microsoft.com>
This allows the guest to put in more than one segment per request. It
can improve the throughput of the system.
Introduce a new check to make sure the queue size configured by the user
is large enough to hold at least one segment.
Signed-off-by: Wei Liu <liuwe@microsoft.com>
Replace `map_or()` on false condition with `is_some_and` to provide
better readability, as suggestted by v1.84.0-beta.1 `cargo clippy`.
Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>
