NSFS | content dir, ignore failure to delete xattr from latest, if already deleted

[nadavMiz]

Describe the Problem

when adding to content dir at the same time after enabling versioning. both of them might try to remove the xattr from the directory. one of them will fail with ENODATA (The named attribute does not exist). ignore this error because attribute already deleted. see removexattr

Explain the Changes

1. ignore xattr clear error for data already deleted

Issues: Fixed #8846

NOTE - issue doesn't replicate on my environment. ran jest tests on CI 15 times without test failing but since it is a concurrency test, there may be other problems that didn't happen by chance

Testing Instructions:

1. run sudo npx jest test_versioning_concurrency -t "content dir multiple puts of the same key"

• Doc added/updated
• Tests added

[shirady]

@nadavMiz.

• If I understand right the underlying system call is fremovexattr man (you referred to removexattr), and there the the error code is ENOATTR, but:

ENOATTR
The named attribute does not exist. (ENOATTR is defined to be a synonym for ENODATA in <attr/xattr.h>.)
If you can explain what I missed.

• Anyway, I saw from the logs that you attached in the issue that it is:

code: ENODATA, context: FileReplacexattr

• I was wondering if we want what you created as a function that we can use in other places in NSFS, but is out of the scope of this PR... (just raising as a thought).

[nadavMiz]

@shirady regarding your comment. in _clear_user_xattr we clear the user xattr from the directory. we check that the xattr exists before clearing them. the issue is that two threads can get to this function together and then one thread deletes the xattr while the second fails with this error because the first already deleted the xattr. and so the The named attribute does not exist. regarding creating a function for this: I am not sure I should do it at this point because its a very specific scenario. but maybe we should consider modifying the existing function so it will not fail in case there are no xattr on the object?

[shirady]

@nadavMiz thank you for the explanation.
I was trying to understand which system cal exactly fails it - fremovexattr or removexattr, if you can show a reference from the code.

[nadavMiz]

@shirady we are using fremovexattr. see clear_xattr in fs_nappi. however both fremovexattr and removexattr have the same errors