Re: [PATCH v3 1/2] pstore: Remove worst-case compression size logic

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Jul 12, 2023 at 06:23:31PM +0200, Ard Biesheuvel wrote:
> The worst case compression size used by pstore gives an upper bound for
> how much the data might inadvertently *grow* due to encapsulation
> overhead if the input is not compressible at all.
> 
> Given that pstore records have individual 'compressed' flags, we can
> simply store the uncompressed data if compressing it would end up using
> more space, making the worst case identical to the uncompressed case.
> 
> This means we can just drop all the elaborate logic that reasons about
> upper bounds for each individual compression algorithm, and just store
> the uncompressed data directly if compression fails for any reason.
> 
> Co-developed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com> # Steam Deck
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  fs/pstore/platform.c | 206 ++------------------
>  1 file changed, 19 insertions(+), 187 deletions(-)

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric