linux-kernel - Re: [PATCH v8 6/7] rust: Add read_poll

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Message-Id: <20250116.203224.774687694231808904.fujita.tomonori@gmail.com>
Date: Thu, 16 Jan 2025 20:32:24 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: aliceryhl@...gle.com
Cc: fujita.tomonori@...il.com, linux-kernel@...r.kernel.org,
 boqun.feng@...il.com, rust-for-linux@...r.kernel.org,
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Subject: Re: [PATCH v8 6/7] rust: Add read_poll_timeout functions

On Thu, 16 Jan 2025 10:45:00 +0100
Alice Ryhl <aliceryhl@...gle.com> wrote:

>> +void __might_sleep(const char *file, int line)
>> +{
>> +       long len = strlen(file);
>> +
>> +       __might_sleep_precision(file, len, line);
>>  }
>>  EXPORT_SYMBOL(__might_sleep);
> 
> I think these strlen() calls could be pretty expensive. You run them
> every time might_sleep() runs even if the check does not fail.

Ah, yes.

> How about changing __might_resched_precision() to accept a length of
> -1 for nul-terminated strings, and having it compute the length with
> strlen only *if* we know that we actually need the length?
> 
> if (len < 0) len = strlen(file);
> pr_err("BUG: sleeping function called from invalid context at %.*s:%d\n",
>        len, file, line);

Works for me.

> Another option might be to compile the lengths at compile-time by
> having the macros use sizeof on __FILE__, but that sounds more tricky
> to get right.

Yeah.

By the way, from what I saw in the discussion about Location::file(),
I got the impression that the feature for a null-terminated string
seems likely to be supported in the near future. Am I correct?

If so, rather than adding a Rust-specific helper function to the C
side, it would be better to solve the problem on the Rust side like
the previous versions with c_str()! and file()! for now?