Fix PATCH operation in virtio-block devices backed by asynchronous engine #4286
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Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## main #4286 +/- ##
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+ Coverage 81.69% 81.71% +0.02%
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Files 240 240
Lines 29293 29332 +39
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+ Hits 23932 23970 +38
- Misses 5361 5362 +1
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ShadowCurse
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kalyazin
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So far, tests for virtio block devices only used the synchronous engine for testing. This commit, uses the "io_engine" fixture which returns both "Sync" and "Async" (for the kernels > 4.14). It also adds a test the we can mount devices after patching the backing file on the host. Signed-off-by: Babis Chalios <[email protected]>
In test test_send_ctrl_alt_del we send a CTRL+ALT+DEL to the microVM, which, in x86, makes the microVM to shutdown. Then we send a signal to the Firecracker process with `os.kill(firecracker_pid, 0)` and wait for it to fail. This works but logs an error in the test logs which can be confusing. Instead we can call os.waitpid() which waits for the Firecracker process to exit and returns immediately if the process has already exited. Signed-off-by: Babis Chalios <[email protected]>
The asynchronous engine maintains an event file descriptor which passes to the IO uring interface when creating a new ring. IO uring uses this EventFd to notify us about completion of IO requests. When we PATCH an async block device, we create a new asynchronous engine, including a new EventFd. However, we still monitor the old EventFd. This breaks the use of async drives post PATCH requests, because we never get notified about the results of requests we submit to the IO uring engine. This commit changes the implementation along the PATCH code path, to reuse the previous EventFd for the asynchronous engine. Signed-off-by: Babis Chalios <[email protected]>
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Changes
Changes the implementation along the PATCH code path for
virtio-blockdevices so that, for the case of asynchronous engines (IO uring), it reuses the existingEventFdfor getting completion callback notifications, rather than creating a knew one.It also modifies the
virtio-blocktests to also test the asynchronous engine. It extends a test that verifies the PATCH operation works to also check thatmount-ing an asynchronous device works.Reason
The asynchronous engine maintains an event file descriptor which passes to the IO uring interface when creating a new ring. IO uring uses this EventFd to notify us about completion of IO requests.
When we PATCH an async block device, we create a new asynchronous engine, including a new EventFd. However, we still monitor the old EventFd. This breaks the use of async drives post PATCH requests, because we never get notified about the results of requests we submit to the IO uring engine.
As a result, mounting a virtio-block device backed from an asynchronous file engine was blocking for ever.
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CONTRIBUTING.md.PR Checklist
CHANGELOG.md.TODOs link to an issue.rust-vmm.