cephfs: free C.CString allocations in OpenSnapDiff

[lawrence3699]

Summary

C.CString() allocates C heap memory that must be freed with C.free(). The 4 string allocations passed to open_snapdiff_dlsym() are never freed, causing a memory leak on every call. If the function returns early due to an error, all 4 strings leak.

Extracted each C.CString() into a named variable with a corresponding defer C.free().

Test plan

• Existing snap_diff tests still pass
• Verify with valgrind/ASAN that the leak is resolved

[Copilot]

Pull request overview

This PR fixes a C-heap memory leak in OpenSnapDiff by ensuring C.CString() allocations are freed after calling into the dynamically-loaded ceph_open_snapdiff wrapper.

Changes:

• Extracted the four C.CString() calls in OpenSnapDiff into named variables.
• Added defer C.free(...) for each allocated C string to guarantee cleanup on success and early-return error paths.

---

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[anoopcs9]

Changes lgtm. See below for some process oriented suggestions:

• Commit message title should mention the component in which the change is proposed. Please replace fix with cephfs.
• Commit message is missing Signed-off-by: tag.

[anoopcs9]

@lawrence3699 Are you planning to work on my above request?

[phlogistonjohn]

@Mergifyio update

[mergify]

update

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[anoopcs9]

@lawrence3699 Are you planning to work on my above request?

I've taken the liberty of rebasing (and fixing the commit‑message title) the PR. @lawrence3699, I'm still unsure which name and email address should appear in the Signed‑off‑by: line. Could you update it or let us know here?

[phlogistonjohn]

@anoopcs9 let's give @lawrence3699 two weeks to respond to your request for Sign-off. If @lawrence3699 is unable to respond by that time I suggest taking the patches into a branch we control and putting a Co-authored-by and then "owning" the patch ourselves with one of our sign offs. The patch is not trivial but it's not complex either and seems pretty straight forward.

I think that would be a good compromise in case lawrence3699 doesn't respond, WDYT?

[nixpanic]

I think that would be a good compromise in case lawrence3699 doesn't respond, WDYT?

That is very reasonable. But for small changes like this I would reduce the time to a few days.

[phlogistonjohn]

Thanks for the suggestion. I had picked two weeks because it's a decent vacation length. :-)

[anoopcs9]

@anoopcs9 let's give @lawrence3699 two weeks to respond to your request for Sign-off. If @lawrence3699 is unable to respond by that time I suggest taking the patches into a branch we control and putting a Co-authored-by and then "owning" the patch ourselves with one of our sign offs. The patch is not trivial but it's not complex either and seems pretty straight forward.

I think that would be a good compromise in case lawrence3699 doesn't respond, WDYT?

Given that the source branch is allowed to be updated by maintainers I've uploaded a modified version. Let me know whether we should proceed with the current branch or create a new one.

[phlogistonjohn]

Sounds good to me.

[phlogistonjohn]

Do we care about the failing pre-squid job? I think it's a packaging issue on the ceph side. But rather than just hit the approve button I felt I should double check.

[anoopcs9]

Do we care about the failing pre-squid job? I think it's a packaging issue on the ceph side. But rather than just hit the approve button I felt I should double check.

I wanted to at least try and see what's wrong, but the squid tag isn't available at the moment. I can only agree that the earlier error is due to some packaging/build issue. Let's not wait any longer.

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-05-11 12:53 UTC · Rule: default
• ✅ Checks skipped · PR is already up-to-date
• ✅ Merged — 2026-05-11 12:53 UTC · at e5c636c1d7ed5974f4cc11d22a4bf2e097a57137 · rebase

This pull request spent 20 seconds in the queue, including 3 seconds running CI.

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  • cephfs: free C.CString allocations in OpenSnapDiff #1254
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  • cephfs: free C.CString allocations in OpenSnapDiff #1254
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