snapshot: Remove max_connections and max_pending_resets fields #4913
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Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## main #4913 +/- ##
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- Coverage 84.10% 84.07% -0.03%
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Files 251 251
Lines 28080 28067 -13
==========================================
- Hits 23616 23597 -19
- Misses 4464 4470 +6
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`TcpIPv4Handler` for MMDS network stack preallocates several buffers whose sizes are saved into a snapshot as `max_connections` and `max_pending_resets` in `MmdsNetworkStackState`. But they are always the same constant hardcoded values (`DEFAULT_MAX_CONNECTIONS` and `DEFAULT_MAX_PENDING_RESETS`) as of today, which means there is no need to save them into a snapshot. Even if we change the hardcoded sizes across Firecracker versions, that should not be a problem. This is because the snapshot feature does not support migration of network connections and those buffers are initialized with empty on snapshot restoration. When migrating from a Firecracker version with larger buffers to another version with smaller ones, guest workloads that worked previously might start to fail due to the less buffer spaces. However, the issue is not a problem of the snapshot feature and it should also occur even on a purely booted microVM (not restored from a snapshot). Thus, it is fine to remove those fields from a snapshot. Since this is a breaking change of the snapshot format, bumps the major version. Signed-off-by: Takahiro Itazuri <[email protected]>
There is no need to use MmdsNetworkStack::new() instead of MmdsNetworkStack::new_with_defaults() in tests that pass the same default values. Signed-off-by: Takahiro Itazuri <[email protected]>
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roypat
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Nov 14, 2024
Not even this can happen I think, because its just the capacity of the data structures. If they reach that capacity, then they'll simply grow :D |
yeah, I'm on the same page. I tried to make excuses at best I could :P |
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| @@ -12,6 +12,10 @@ and this project adheres to | |||
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| ### Changed | |||
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| - [#4913](https://github.com/firecracker-microvm/firecracker/pull/4913): Removed | |||
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Not opposing the change, but what are customers supposed to do in response to this?
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Good point, they need to regenerate a snapshot. We might want to apply the same fix for the previous change.
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Changes
Remove
max_connectionsandmax_pending_resetsfields from snapshot.Note that I only focused on removing them in this PR although I might open another PR to refactor more later.
Reason
TcpIPv4Handlerfor MMDS network stack preallocates several bufferswhose sizes are saved into a snapshot as
max_connectionsandmax_pending_resetsinMmdsNetworkStackState. But they are always thesame constant hardcoded values (
DEFAULT_MAX_CONNECTIONSandDEFAULT_MAX_PENDING_RESETS) as of today, which means there is no needto save them into a snapshot. Even if we change the hardcoded sizes
across Firecracker versions, that should not be a problem. This is
because the snapshot feature does not support migration of network
connections and those buffers are initialized with empty on snapshot
restoration. When migrating from a Firecracker version with larger
buffers to another version with smaller ones, guest workloads that
worked previously might start to fail due to the less buffer spaces.
However, the issue is not a problem of the snapshot feature and it
should also occur even on a purely booted microVM (not restored from a
snapshot). Thus, it is fine to remove those fields from a snapshot.
Since this is a breaking change of the snapshot format, bumps the major
version.
License Acceptance
By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license. For more information on following Developer
Certificate of Origin and signing off your commits, please check
CONTRIBUTING.md.PR Checklist
tools/devtool checkstyleto verify that the PR passes theautomated style checks.
how they are solving the problem in a clear and encompassing way.
[ ] I have updated any relevant documentation (both in code and in the docs)in the PR.
CHANGELOG.md.[ ] If a specific issue led to this PR, this PR closes the issue.[ ] When making API changes, I have followed theRunbook for Firecracker API changes.
integration tests.
[ ] I have linked an issue to every newTODO.rust-vmm.