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Clarifying from_err_ptr may return Ok(NULL) #1231
Description
Please read https://lore.kernel.org/rust-for-linux/20260322193830.89324-1-ojeda@kernel.org/ for context -- this issue is about this part:
- On the Rust general infrastructure side, we should document more
prominently that `from_err_ptr` may return `Ok(NULL)` just fine,
since it calls `IS_ERR`. It may be obvious, since `NULL` is not an
error value, but still, it could have perhaps prevented this issue.
We should also include an example to the doctest showing and testing
that particular case to drive the point home.
Regarding the doctest part: it should be a new one, or the existing one should be made non-ignore.
In addition, the example should assert not just for Ok(NULL), but also other cases.
This requires submitting a proper patch to the LKML and the Rust for Linux mailing list. Please recall to test your changes (including generating the documentation if changed, running the Rust doctests if changed, etc.), to use a proper title for the commit, to sign your commit under the Developer's Certificate of Origin and to add a Suggested-by: tag, and a Link: tag to this issue. Please see https://docs.kernel.org/process/submitting-patches.html and https://rust-for-linux.com/contributing for details.
Activity
Mirko-A commentedon Mar 27, 2026
Hi Miguel, may I take this up?
ojeda commentedon Mar 27, 2026
Of course, please feel free to send a patch!
Mirko-A commentedon Mar 28, 2026
Thanks, I've just sent one out.
I listed the recipients of your original email as the recipients of mine, and added the rest of maintainers listed by
get_maintainer.plas cc. I hope I didn't leave anyone out.Mirko-A commentedon Mar 28, 2026
After sending out the patch I tried getting the doctest to fail and realized that, the way I submitted it, it does not get executed at all. I had the asserts outside the functions when testing initially but then chose to move them inside, which broke the doctest.
I apologize for the mistake, I will try to be more careful in the future.
ojeda commentedon Mar 28, 2026
No worries, it is part of learning :)
https://lore.kernel.org/rust-for-linux/20260328114005.125617-1-adzicmirko97@gmail.com/
I have replied in the list.
rust: error: clarify that `from_err_ptr` can return `Ok(NULL)`
rust: error: clarify that `from_err_ptr` can return `Ok(NULL)`
rust: error: clarify that `from_err_ptr` can return `Ok(NULL)`
rust: error: clarify that `from_err_ptr` can return `Ok(NULL)`
rust: error: clarify that `from_err_ptr` can return `Ok(NULL)`