Re: [RFC v3 3/7] mm: Use seprintf() instead of less ergonomic APIs

[Linus Torvalds <torvalds@linux-foundation.org>]

On Mon, 7 Jul 2025 at 12:35, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> Lifting struct membuf out of include/linux/regset.h, perhaps, and
> adding printf to the family?

membuf has its own problems. It doesn't remember the beginning of the
buffer, so while it's good for "fill in this buffer with streaming
data", it's pretty bad for "let's declare a buffer, fill it in, and
then use the buffer for something".

So with membuf, you can do that "fill this buffer" cleanly.

But you can't then do that "ok, it's filled, now flush it" - not
without passing in some other data (namely the original buffer data).

I don't exactly love "struct seq_buf" either - it's big and wasteful
because it has 64-bit sizes - but it at least *retains* the full
state, so you can do things like "print to this buffer" and "flush
this buffer" *without* passing around extra data.

              Linus