fix: stop dup(2)-ing fds when setting up guest memory
#5026
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Currently, when backing guest memory by memfd or when mmaping a snapshot file, we duplicate the file descriptor once per memslot. This is not necessary: KVM will happily accept the same fd into multiple memslots, and even rust-vmm supports APIs for this (by storing `Arc<File>` instead of just `File` in `FileOffset`, we can actually share the same `File` reference between multiple memory regions). So let's make use of this capability. Signed-off-by: Patrick Roy <roypat@amazon.co.uk>
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## main #5026 +/- ##
=======================================
Coverage 83.16% 83.16%
=======================================
Files 245 245
Lines 26647 26647
=======================================
Hits 22161 22161
Misses 4486 4486
Flags with carried forward coverage won't be shown. Click here to find out more. ☔ View full report in Codecov by Sentry. |
roypat
added
the
Status: Awaiting review
ShadowCurse
approved these changes
Feb 5, 2025
kalyazin
approved these changes
Feb 5, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Currently, when backing guest memory by memfd or when mmaping a snapshot file, we duplicate the file descriptor once per memslot. This is not necessary: KVM will happily accept the same fd into multiple memslots, and even rust-vmm supports APIs for this (by storing
Arc<File>instead of justFileinFileOffset, we can actually share the sameFilereference between multiple memory regions). So let's make use of this capability.Changes
...
Reason
...
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.
in the PR.
CHANGELOG.md.Runbook for Firecracker API changes.
integration tests.
TODO.rust-vmm.