Commit Graph

2190 Commits

Author SHA1 Message Date
Peter Oskolkov
aa8e9cd91a misc: Change cpu ID type from u8 to u32
This is the first change to Cloud Hypervisor in a series of changes
intended to increase the max number of supported vCPUs in guest VMs,
which is currently limited to 255 (254 on x86_64).

No user-visible/behavior changes are expected as a result of
applying this patch, as the type of boot_cpus and related
fields in config structs remains u8 for now, and all configuration
validations remain the same.

Signed-off-by: Barret Rhoden <brho@google.com>
Signed-off-by: Neel Natu <neelnatu@google.com>
Signed-off-by: Ofir Weisse <oweisse@google.com>
Signed-off-by: Peter Oskolkov <posk@google.com>
2025-08-11 20:31:50 +00:00
Alex Orozco
a70c1b38e7 devices: Add fw_cfg cli options
This allows us to enable/disable the fw_cfg device via the cli

We can also now upload files into the guest vm using fw_cfg_items
via the cli

Signed-off-by: Alex Orozco <alexorozco@google.com>
2025-08-11 17:29:51 +00:00
Alex Orozco
971f552e09 vmm: Add acpi table for fw_cfg device
This allows the fw_cfg device to be recognized by the guest linux
kernel. This becomes more relavnt in the following cl where I add
the option to load files into the guest via fw_cfg. The Linux kernel
already has a fw_cfg driver that will automatically load these files
under /sys when CONFIG_FW_CFG_SYSFS is enabled in the kernel config

For arm we must add fw_cfg to the devices tree

Signed-off-by: Alex Orozco <alexorozco@google.com>
2025-08-11 17:29:51 +00:00
Alex Orozco
edee53ac1a devices: Implement DMA for fw_cfg device
We pass a reference to the guest memory when we create the device
in DeviceManager. This allows us to access the guest memory for DMA.

Signed-off-by: Alex Orozco <alexorozco@google.com>
2025-08-11 17:29:51 +00:00
Alex Orozco
1f51e4525b devices: Add acpi tables to fw_cfg
The acpi tables are created in the same place the acpi tables would be
created for the regular bootflow, except here we add them to the
fw_cfg device to be measured by the fw and then the fw will put the
acpi tables into memory.

Signed-off-by: Alex Orozco <alexorozco@google.com>
2025-08-11 17:29:51 +00:00
Alex Orozco
f0b69d56d0 devices: Add e820/memory_map to fw_cfg device
We build the memory map in the fw_cfg device based on the memory size.

Signed-off-by: Alex Orozco <alexorozco@google.com>
2025-08-11 17:29:51 +00:00
Alex Orozco
623fadfa9d devices: Add kernel cmdline, kernel, and initramfs to fw_cfg device
The kernel and initramfs are passed to the fw_cfg device as
file references. The cmdline is passed directly.

Signed-off-by: Alex Orozco <alexorozco@google.com>
2025-08-11 17:29:51 +00:00
Alex Orozco
777b7ee11e devices: Add fw_cfg device
Here we add the fw_cfg device as a legacy device to the device manager.
It is guarded behind a fw_cfg flag in vmm at creation of the
DeviceManager. In this cl we implement the fw_cfg device with one
function (signature).

Signed-off-by: Alex Orozco <alexorozco@google.com>
2025-08-11 17:29:51 +00:00
Ruoqing He
17195e1a46 vmm: Enable firmware boot for riscv64
Implement firmware boot (UEFI boot) for riscv64 architecture.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>
2025-08-11 10:10:27 +00:00
Ruoqing He
0df4b1ac4f vmm: Define riscv64 UEFI Error
Error::UefiLoad is required for load_firmware to propagate errors
encountered, define it for riscv64.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>
2025-08-11 10:10:27 +00:00
Ruoqing He
2e0ec8095c vmm: Enable uefi_flash field for riscv64
uefi_flash field in memory_manager is required for uefi loading and
booting, enable it for riscv64 architecture.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>
2025-08-11 10:10:27 +00:00
Songqian Li
cd2c43b489 misc: Fix beta clippy errors
Fix clippy error: "error: manual implementation of `.is_multiple_of()
`" from rustc 1.90.0-beta.1 (788da80fc 2025-08-04).

Signed-off-by: Songqian Li <sionli@tencent.com>
2025-08-07 16:53:59 +00:00
Bo Chen
394fd230b0 vmm: acpi: Clarify the return of 'create_acpi_tables_internal'
Signed-off-by: Bo Chen <bchen@crusoe.ai>
2025-08-06 21:11:27 +00:00
Bo Chen
abcec231eb vmm: acpi: Clarify variable naming in 'create_acpi_tables_internal'
When generating ACPI tables, we are not using "offset", instead we
are using (guest physical) addresses.

Signed-off-by: Bo Chen <bchen@crusoe.ai>
2025-08-06 21:11:27 +00:00
Bo Chen
cda1ea53a5 vmm: acpi: Make 'create_acpi_tables' more flexible
Now 'create_acpi_tables_internal()' can generate ACPI tables with
different dsdt offset, so that it can be reused for generating ACPI
tables for `fw_cfg`.

Signed-off-by: Bo Chen <bchen@crusoe.ai>
Signed-off-by: Alex Orozco <alexorozco@google.com>
2025-08-06 21:11:27 +00:00
Muminul Islam
8e010f1aa3 vmm: don't configure system if rsdp is not available
In case of CVM guest rsdp is set to none. Unwrapping it
make the vmm crashed. Don't call configure system if the
rsdb address is none.

Signed-off-by: Muminul Islam <muislam@microsoft.com>
2025-07-29 15:55:06 +00:00
Jean-Philippe Brucker
4528e2f1ea devices: rtc_pl031: Disable broken interrupt
The PL031 RTC provides two features: a real-time counter and an alarm
interrupt. To use the alarm, the driver normally writes a time value
into the match register RTCMR, and when the counter reaches that value
the device triggers the interrupt.

At the moment the implementation ignores programming of the alarm, as
the feature seems rarely used in VMs. However the interrupt is still
triggered arbitrarily when the guest writes to registers, and the line
is never cleared. This really confuses the Linux driver, which loops in
the interrupt handler until Linux realizes that no one is dealing with
the interrupt (200000 unanswered calls) and disables the handler.

One way to fix this would be implementing the alarm function properly,
which isn't too difficult but requires adding some async timer logic
which probably won't ever get used. In addition the device's interrupt
is level-triggered and we don't support level interrupts at the moment,
though we could probably get away with changing this interrupt to edge.

The simplest fix, though, is to just disable the interrupt logic
entirely, so that the alarm function still doesn't work but the guest
doesn't see spurious interrupts.

Add a default() implementation to satisfy clippy's new_without_default
check, since Rtc::new() doesn't take a parameter after this change.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
2025-07-17 17:21:05 +00:00
Ruoqing He
6da5c32fd9 hypervisor: aarch64: Use offset_of for nested fields
`std::mem::offset_of` could be used for calculating nested fields, use
this feature to shorten aarch64 reg offset calculation.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>
2025-07-10 16:39:39 +00:00
Philipp Schuster
9d4408ba76 vmm: add directory path to error message
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-07-10 16:24:50 +00:00
Maximilian Güntner
f9c134471a vmm: warn about deprecation of default IP address + mask
Issue: #7083

Signed-off-by: Maximilian Güntner <code@mguentner.de>
2025-07-08 19:05:45 +00:00
ninollei
3d5b4d0b0c vmm: acpi: Use correct table name in error message
Fix a copy-paste error using the wrong table name in the assertion

Signed-off-by: ninollei <ninollx@hotmail.com>
2025-07-08 09:02:40 +00:00
Philipp Schuster
d580ed55c6 seccomp: add SYS_getcwd (79) to support proper Rust backtraces
When a proper Rust backtrace is printed, the Rust std wants to use the
SYS_getcwd(79) system call to prettify some paths while printing. In
Cloud Hypervisor, this is at least relevant for printing panics or if
a `anyhow::Error` value is printed using `{e:?}` (but not `{e:#?}`).

The syscall cause can be found in `impl fmt::Display for Backtrace {}`
in `library/std/src/backtrace.rs`.

Without this addition, the seccomp violation of the SYS_getcwd (79)
hinders the proper error message including a full backtrace from showing
up. This annoying behaviour already delayed many debugging efforts. With
this fix, things just work. The new syscall itself should be pretty
harmless for normal operation.

```
thread 'vmm' panicked at virtio-devices/src/rng.rs:224:9:
Yikes, things went horribly wrong!

==== Possible seccomp violation ====
Try running with `strace -ff` to identify the cause and open an issue: https://github.com/cloud-hypervisor/cloud-hypervisor/issues/new
[1]    287683 invalid system call (core dumped)  RUST_BACKTRACE=full cargo run --bin cloud-hypervisor -- --api-socket  --kerne
```

```
thread 'vmm' panicked at virtio-devices/src/rng.rs:224:9:
Yikes, things went horribly wrong!
stack backtrace:
   0:     0x557d91286b62 - std::backtrace_rs::backtrace::libunwind::trace::hc20b48b31ee52608
                               at /rustc/17067e9ac6d7ecb70e50f92c1944e545188d2359/library/std/src/../../backtrace/src/backtrace/libunwind.rs:117:9
   1:     0x557d91286b62 - std::backtrace_rs::backtrace::trace_unsynchronized::h5d207cd20f193d88
                               at /rustc/17067e9ac6d7ecb70e50f92c1944e545188d2359/library/std/src/../../backtrace/src/backtrace/mod.rs:66:14

...

  67:                0x0 - <unknown>
Error: Cloud Hypervisor exited with the following error:
  Failed to join on VMM thread: Any { .. }

Debug Info: ThreadJoin(Any { .. })
```

- add any panic, for example into the create or drop function of a
  device
- add --seccomp=true|log to analyze the situation

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-06-26 20:50:57 +00:00
Demi Marie Obenour
24998c1672 vmm: do not treat libc::MAP_FAILED as a pointer
It will likely be safely rejected by the kernel, but it's still wrong.

Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
2025-06-23 09:06:32 +00:00
Philipp Schuster
4182ef91e0 misc: remove once_cell; superseded by std::*
We now have types in the Rust standard library.
Dropping the dependency.

I found this by using the `clippy::pedantic` group.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-06-21 14:25:20 +00:00
Philipp Schuster
a991de9955 vmm: streamline Display impl of Error types
Streamlines the code base by using thiserror's #[error] attribute
consistently for implementing `Display`.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-06-20 10:19:35 +00:00
Philipp Schuster
190a11f212 ch-remote: also pretty-print remote server errors
Remote server errors are transferred as raw HTTP body. This way,
we lose the nested structured error information.

This is an attempt to retrieve the errors from the HTTP response
and to align the output with the normal error output.

For example, this produces the following chain of errors. Note
that everything after level 0 was retrieved from the HTTP server
response:

```
Error: ch-remote exited with the following chain of errors:
  0: http client error
  1: Server responded with InternalServerError
  2: Error from API
  3: The disk could not be added to the VM
  4: Failed to validate config
  5: Identifier disk1 is not unique

Debug Info: HttpApiClient(ServerResponse(InternalServerError, Some("Error from API<br>The disk could not be added to the VM<br>Failed to validate config<br>Identifier disk1 is not unique")))
```

In case the JSON can't be parsed properly, ch-remote will print:

```
Error: ch-remote exited with the following chain of errors:
  0: http client error
  X: Can't get remote's error messages from JSON response: EOF while parsing a value at line 1 column 0: body=''

Debug Info: HttpApiClient(ServerResponse(InternalServerError, Some("")))
```

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-06-13 19:55:54 +00:00
Philipp Schuster
060c9de07f vmm: introduce nice error messages on exit (CHV and ch-remote)
With the foundations of each error type implementing std::error::Error,
we can now nicely walk the `.source()` chain and print an error trace.

This commit introduces improved user-facing error printing when:
- Cloud Hypervisor fails with an error
- ch-remote fails (client error)
- ch-remote fails (remote error)

The additional context is a clear improvement in UX for both users and
developers. In the following example, the new behaviour is shown for
a direct invocation of Cloud Hypervisor leading to a failure. This
looks similar for ch-remote.

```
Old Style
`target/release/cloud-hypervisor --api-socket /tmp/chv2.sock --kernel /etc/bootitems/linux/kernel_minimal/stable.bzImage --cmdline console=ttyS0 --serial tty --console off --disk path=img.raw --initramfs /etc/bootitems/linux/initrd_minimal/default`

Error booting VM: VmBoot(LockingError(BlockError(LockDiskImage(AlreadyLocked)))
```

```
`target/release/cloud-hypervisor --api-socket /tmp/chv2.sock --kernel /etc/bootitems/linux/kernel_minimal/stable.bzImage --cmdline console=ttyS0 --serial tty --console off --disk path=img.raw --initramfs
/etc/bootitems/linux/initrd_minimal/default`

Error: Cloud Hypervisor exited with the following chain of errors:
  0: Error booting VM
  1: The VM could not boot
  2: Error locking disk images: Another instance likely holds a lock
  3: Cannot lock images of all block devices
  4: Failed to get Write lock for disk image: ./img.raw
  5: The file is already locked

Debug Info: VmBoot(VmBoot(LockingError(DiskLockError(LockDiskImage { error: AlreadyLocked, lock_type: Write, path: "./raw_disk.bin" })))
```

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-06-13 19:55:54 +00:00
Philipp Schuster
d7edd9d51f misc: vmm: streamline error Display::fmt()
The changes were mostly automatically applied using the following
Python script:

```python
import os, re

for root, _, files in os.walk("."):
    for f in files:
        if not f.endswith(".rs"):
            continue
        p = os.path.join(root, f)
        with open(p, "r", encoding="utf-8") as file:
            lines = file.readlines()
        changed = False
        for i in range(len(lines) - 1):
            if re.search(r'#\[error\(".*: \{0[^}]*\}"\)\]', lines[i]) and "#[source]" in lines[i + 1].strip():
                lines[i] = re.sub(r': \{0[^}]*\}"\)\]', '")]', lines[i])
                changed = True
        if changed:
            with open(p, "w", encoding="utf-8") as file:
                file.writelines(lines)
            print("Fixed:", p)
```

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

# Conflicts:
#	vmm/src/api/http/mod.rs
2025-06-13 19:55:54 +00:00
Philipp Schuster
4987d63b6a vmm: fix typo
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-06-13 19:55:54 +00:00
Philipp Schuster
9bd9c0cb71 misc: replace manual From<T> for *Error with #[from]
This is a small simplification we can use since we use `thiserror`
anyway. Note that `#[from]` implies `#[source]` [0].

[0]: https://docs.rs/thiserror/2.0.12/thiserror/index.html

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-06-12 15:55:54 +00:00
Jinrong Liang
f151fdb16f vmm: config: Add tests for check block serial length
Signed-off-by: Jinrong Liang <cloudliang@tencent.com>
2025-06-12 13:51:52 +00:00
Jinrong Liang
bb6ca56fb0 vmm: config: Add DiskConfig check for device serial length
Signed-off-by: Jinrong Liang <cloudliang@tencent.com>
2025-06-12 13:51:52 +00:00
Jinank Jain
2bc8d51a60 misc: Fix missing lifetime syntax clippy warning
This was caught by the nightly compiler during cargo fuzz build.

error: lifetime flowing from input to output with different syntax can be confusing
   --> /home/runner/work/cloud-hypervisor/cloud-hypervisor/hypervisor/src/arch/x86/emulator/mod.rs:493:26
    |
493 |     pub fn new(platform: &mut dyn PlatformEmulator<CpuState = T>) -> Emulator<T> {
    |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^     ----------- the lifetime gets resolved as `'_`
    |                          |
    |                          this lifetime flows to the output
    |
    = note: `-D mismatched-lifetime-syntaxes` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(mismatched_lifetime_syntaxes)]`
help: one option is to remove the lifetime for references and use the anonymous lifetime for paths
    |
493 |     pub fn new(platform: &mut dyn PlatformEmulator<CpuState = T>) -> Emulator<'_, T> {

Signed-off-by: Jinank Jain <jinankjain@microsoft.com>
2025-06-09 11:19:11 +00:00
Jinank Jain
51002f2bae build: Bump zbus from 4.4.0 to 5.7.1
Along with this also fix some API incompatibilities issues.

Signed-off-by: Jinank Jain <jinankjain@microsoft.com>
2025-06-09 11:19:11 +00:00
Philipp Schuster
d6ed74b5b8 tests: fix vCPU test relying on specific Display formatting
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-05-30 19:07:15 +00:00
Bo Chen
7571e93a69 vmm: Deprecate SGX support
This commit adds the warning to deprecate the SGX support with the
intention to remove the support from code base in two release cycles.

See: #6960

Signed-off-by: Bo Chen <bchen@crusoe.ai>
2025-05-22 17:41:32 +00:00
Philipp Schuster
517ea00bd9 misc: vmm/api: streamline #[source] and Error impl
This streamlines the Error implementation in the Cloud Hypervisor code
base to match the remaining parts so that everything follows the agreed
conventions. These are leftovers missed in the previous commits.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-05-22 15:13:27 +00:00
Thomas Prescher
d46517559b vmm: don't allow resizing to 0 vCPUs
No sane guest OS will allow hotplugging all cpus.
However, the REST API currently allows specifying
`ch-remote resize --cpus 0`.

On Linux, we can then observe the following error in the kernel log:

processor cpu0: Offline failed.

Subsequent resize commands via ch-remote will then fail with
VcpuPendingRemovedVcpu because the removal of cpu0 was never
successful.

Fix this by disallowing resizing to zero vCPUs.

Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>
On-behalf-of: SAP thomas.prescher@sap.com
2025-05-21 15:28:22 +00:00
Paolo Bonzini
0463f4f156 vmm: use MmapRegion::bitmap() directly
For use in QEMU, I would like GuestMemoryRegion to return a BitmapSlice
instead of a &Bitmap.  This adds some flexibility that QEMU needs in
order to support a single global dirty bitmap that is sliced by the
various GuestMemoryRegions.

However, this removes access to the methods of AtomicBitmap, and in
particular reset() and get_and_reset().  Fortunately, cloud-hypervisor
always uses GuestMemoryMmap, and therefore `region` is known to be a
&GuestRegionMmap.  Dereferencing it returns the MmapRegion to which the
bitmap is attached, thus calling MmapRegion::bitmap(); this has the
same effect as `<GuestRegionMmap as GuestRegion>::bitmap()`, and works
both with or without https://github.com/rust-vmm/vm-memory/pull/324.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2025-05-21 13:00:07 +00:00
Philipp Schuster
fff62d9302 misc: vmm: streamline #[source] and Error
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
2025-05-21 09:09:30 +00:00
Philipp Schuster
a212343908 misc: arch/riscv64: streamline #[source] and Error
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
2025-05-21 09:09:30 +00:00
Gregory Anders
dce82a34d0 net_util: add support for IPv6 addresses on tap interfaces
Allow tap interfaces to be configured with an IPv6 address. The change
is fairly straightforward: we need to update the API types and CLI
parsing to accept either an IPv6 or IPv4 and then match on the IP
address type when the tap device is configured.

For IPv6 addresses, the netmask (prefix) must be provided at the same
time as the address itself (in the SIOCSIFADDR ioctl). They cannot be
configured separately. So we remove the separate "set_netmask" function
and convert "set_ip_addr" to also accept a netmask. For IPv4 addresses,
the IP address and netmask were already always set together, so this
should have no functional impact for users of IPv4 addresses.

Signed-off-by: Gregory Anders <ganders@cloudflare.com>
2025-05-20 16:41:04 +00:00
Philipp Schuster
67793ca375 vmm: improve disk locking error message
This adds guidance on how to resolve the issue.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-05-19 15:13:01 +01:00
Philipp Schuster
96deca9dc9 vmm: streamline display format for DeviceManagerError
This format is also used elsewhere.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>

On-behalf-of: SAP <philipp.schuster@sap.com>
2025-05-16 11:42:01 +00:00
Philipp Schuster
78b0f68b21 vmm: Error for MemoryManagerError
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>

On-behalf-of: SAP <philipp.schuster@sap.com>
2025-05-16 11:42:01 +00:00
Philipp Schuster
a007b750ff vmm: Error for PciDeviceError and PciRootError
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>

On-behalf-of: SAP <philipp.schuster@sap.com>
2025-05-16 11:42:01 +00:00
Philipp Schuster
b2993fb2fa vmm: Error for vsock::unix::Error
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-05-16 11:42:01 +00:00
Philipp Schuster
8d11bf7979 vmm: Error for DeviceManagerError
The DeviceManagerError type is among the types missing the Error trait
so far. To streamline the code and to simplify usage on higher levels
of this error type, this type now implements Display and Error.

As not all variant values are Error yet, `#[source]` is not everywhere
where it could be. This is done in the next commits.

The high level goal is: Enable future work to improve the error output
of cloud hypervisor.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-05-16 11:42:01 +00:00
Philipp Schuster
05968f5c2c block: introduce advisory locks for disk image files
# 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
2025-05-16 08:07:32 +00:00
Philipp Schuster
a23d4b7cf2 block: fixing typo, increase clarity
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
2025-05-16 08:07:32 +00:00