Re: [PATCH v2 1/8] lib/printbuf: New data structure for heap-allocated strings

Steven Rostedt
2022-04-22T22:54:13Z

On Fri, 22 Apr 2022 17:51:46 -0400
Kent Overstreet <kent.overstreet@gmail.com> wrote:

>
> But it's definitely not an unreasonable idea - I can try it out and see how it
> turns out. Would you have any objections to making some changes to seq_buf?

No I don't mind, and that's why I want the coupled, as enhancements or bug
fixes would happen to both.

>
> - You've got size and len as size_t, I've got them as unsigned. Given that we
> need to be checking for overflow anyways for correctens, I like having them
> as u32s.

I had it as size_t as I had planned (and still plan to) make seq_file use
seq_buf, and seq_file uses size_t. Who knows, perhaps in the future, we may
have strings that are more than 4GBs. ;-)

> - seq_buf->readpos - it looks like this is only used by seq_buf_to_user(), does
> it need to be in seq_buf?

Perhaps.

> - in printbufs, I make sure the buffer is always nul-terminated - seems
> simplest, given that we need to make sure there's always room for the
> terminating nul anyways.

I'm not against that. It was an optimization, but I never actually
benchmarked it. But I'm not sure how many fast paths it is used in to
warrant that kind of optimization over the complexity it can bring for
users.

>
> A downside of having printbuf on top of seq_buf is that now we've got two apis
> that functions can output to - vs. if we modified printbuf by adding a flag for
> "this is an external buffer, don't reallocate it". That approach would be less
> code overall, for sure.
>
> Could I get you to look over printbuf and share your thoughts on the different
> approaches?

Sure, but will have to wait till next week.

-- Steve