From: Yann Droneaud <ydroneaud@opteya.com>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Kees Cook <keescook@chromium.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Herbert Xu <herbert@gondor.apana.org.au>,
Theodore Ts'o <tytso@mit.edu>,
linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 3/5] random: add helpers for random numbers with given floor or range
Date: Tue, 15 Nov 2022 09:42:25 +0100 [thread overview]
Message-ID: <9ffb34a9-3cbc-bd0e-7a92-76851a77b9ef@opteya.com> (raw)
In-Reply-To: <Y3KLH4FqFbJ7bfY0@zx2c4.com>
Hi,
Le 14/11/2022 à 19:38, Jason A. Donenfeld a écrit :
> On Mon, Nov 14, 2022 at 07:04:13PM +0100, Yann Droneaud wrote:
>> I have a bad feeling about this one, and can't help but thinking it's going
>> to bite someone: when asked to pick a number *between* 0 and 10,
>> I usually think I'm allowed to pick 10 (even if I'm going to answer 7 as it should).
> This is one of those bikeshed things you see all over the place, like
> whether slices in a language should be [start index, end index] or
> [start index, length], or whether arrays should be 0-based or 1-based.
> We'll never settle this variety of dispute here.
>
> But in this case, there are some particular reasons why it must be this
> way. Firstly, usage of it this way matches most of the ways the function
> is actually used in the kernel, and fits existing semantics. This alone
> I find compelling. But also, having all of these functions use half-open
> intervals means that each function can take care of its entire range,
> without having to resort to using 64-bit arithmetic, and no function is
> a complete subset of any other function. So doing it this way makes
> these maximally useful too.
For get_random_below(), which replaces a modulo, <bikeshedding> and could
have been called get_random_mod()</bikeshedding>, having an open upper
range seems fine. It's already what can be achieved by the % operator.
But I believe it's unfortunate get_random_between() cannot be called to
get a number up to UINT32_MAX, as get_random_between(0, UINT32_MAX) would
be capped to UINT32_MAX - 1.
When not a constant, one could hope the function can cope with a maximum
that would grow up to and including UINT32_MAX.
> So anyway I think the function has to be defined like this. If you'd
> like to bikeshed over a different name than "between", though, be my
> guest. Maybe you'd like "from" better. But probably "between" is fine,
> and with enough good examples (as my conversion patch does) and the
> clear succinct documentation comment, we should be good.
That the conversion patch [1] that triggered my comment: I find replacing
the following rather unpleasing, somewhat uncanny:
-get_random_u32_below(1024) + 1 + get_random_u32_between(1, 1024 + 1) I
would prefer
- get_random_u32_below(1024) + 1 + get_random_u32_between(1, 1024) [1]https://lore.kernel.org/lkml/20221114164558.1180362-4-Jason@zx2c4.com/
Regards.
--
Yann Droneaud
OPTEYA
next prev parent reply other threads:[~2022-11-15 8:42 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-22 1:43 [PATCH v1 0/5] convert tree to get_random_u32_{below,above,between}() Jason A. Donenfeld
2022-10-22 1:43 ` [PATCH v1 1/5] treewide: use get_random_u32_below() instead of deprecated function Jason A. Donenfeld
2022-10-22 2:25 ` Darrick J. Wong
2022-10-22 18:44 ` SeongJae Park
2022-10-22 1:44 ` [PATCH v1 2/5] prandom: remove prandom_u32_max() Jason A. Donenfeld
2022-10-22 1:44 ` [PATCH v1 3/5] random: add helpers for random numbers with given floor or range Jason A. Donenfeld
2022-11-14 18:04 ` Yann Droneaud
2022-11-14 18:38 ` Jason A. Donenfeld
2022-11-15 8:42 ` Yann Droneaud [this message]
2022-11-16 0:25 ` Jason A. Donenfeld
2022-10-22 1:44 ` [PATCH v1 4/5] treewide: use get_random_u32_{above,below}() instead of manual loop Jason A. Donenfeld
2022-10-22 1:44 ` [PATCH v1 5/5] treewide: use get_random_u32_between() when possible Jason A. Donenfeld
2022-10-22 3:55 ` [PATCH v1 0/5] convert tree to get_random_u32_{below,above,between}() Jakub Kicinski
2022-10-22 4:23 ` Jason A. Donenfeld
2022-10-22 5:32 ` Jakub Kicinski
2022-10-22 5:47 ` Jason A. Donenfeld
2022-10-22 6:03 ` Jakub Kicinski
2022-10-23 21:07 ` Theodore Ts'o
2022-10-24 16:43 ` Jason A. Donenfeld
2022-10-22 10:21 ` Greg Kroah-Hartman
2022-10-24 16:37 ` Jason Gunthorpe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=9ffb34a9-3cbc-bd0e-7a92-76851a77b9ef@opteya.com \
--to=ydroneaud@opteya.com \
--cc=Jason@zx2c4.com \
--cc=gregkh@linuxfoundation.org \
--cc=herbert@gondor.apana.org.au \
--cc=keescook@chromium.org \
--cc=linux-crypto@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=tytso@mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).