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    SubjectRe: [PATCH v3 03/33] vsprintf: Convert to printbuf
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    On 04/06/2022 21.30, Kent Overstreet wrote:
    > This converts vsnprintf() to printbufs: instead of passing around raw
    > char * pointers for current buf position and end of buf, we have a real
    > type!
    >
    > This makes the calling convention for our existing pretty printers a lot
    > saner and less error prone, plus printbufs add some new helpers that
    > make the code smaller and more readable, with a lot less crazy pointer
    > arithmetic.
    >
    > There are a lot more refactorings to be done: this patch tries to stick
    > to just converting the calling conventions, as that needs to be done all
    > at once in order to avoid introducing a ton of wrappers that will just
    > be deleted.
    >
    > Thankfully we have good unit tests for printf, and they have been run
    > and are all passing with this patch.

    So, as the primary author of those tests, a somewhat active contributor
    to vsprintf.c and being listed as R: for both files, why wasn't I cc'ed
    on this?

    Anyway, my main concern with this is that performance goes down the
    drain and the generated code will be awful. Have you done any
    measurements and/or looked at disassembly? Thanks to
    -fno-strict-aliasing (or perhaps just because we're writing through a
    char* pointer which IIRC may alias anything), I think the compiler will
    be forced to reload prt->pos and prt->size over and over and over. I may
    be wrong, of course, that happens often. Perhaps __restrict could help, IDK.

    > ---
    > include/linux/kernel.h | 4 +

    Please don't expand that dumping ground. Please, if printbufs will
    become a thing (whether or not vsprintf internally will be refactored to
    use them), add a new linux/printf.h where these things can go, and the
    declarations of vsprintf() and close friends can eventually be moved.

    Rasmus

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