linux-kernel - Re: rfc: treewide scripted patch mechanism? (was: Re: [PATCH] Makefile: Convert -Wimplicit-fallthrough=3 to just -Wimplicit-fallthrough for clang)QUILT

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Date:   Tue, 20 Aug 2019 16:37:27 -0700
From:   Joe Perches <joe@...ches.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Julia Lawall <julia.lawall@...6.fr>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com,
        Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: rfc: treewide scripted patch mechanism? (was: Re: [PATCH]
 Makefile: Convert -Wimplicit-fallthrough=3 to just -Wimplicit-fallthrough
 for clang)QUILT

On Tue, 2019-08-20 at 16:28 -0700, Linus Torvalds wrote:
> On Mon, Aug 19, 2019 at 5:08 PM Joe Perches <joe@...ches.com> wrote:
> > 2: would be Julia Lawall's stracpy change done
> > with coccinelle: (attached)
> 
> I'm not actually convinced about stracpy() and friends.
> 
> It seems to be yet another badly thought out string interface, and
> there are now so many of them that no human being can keep track of
> them.
> 
> The "badly thought out" part is that it (like the original strlcpy
> garbage from BSD) thinks that there is only one size that matters -
> the destination.
> 
> Yes, we fixed part of the "source is also limited" with strscpy(). It
> didn't fix the problem with different size limits, but at least it
> fixed the fundamentally broken assumption that the source has no size
> limit at all.
> 
> Honestly, I really really REALLY don't want yet another broken string
> handling function, when we still have a lot of the old strlcpy() stuff
> in the tree from previous broken garbage.
> 
> The fact is, when you copy strings, both the destination *AND* the
> source may have size limits. They may be the same. Or they may not be.
> 
> This is particularly noticeable in the "str*_pad()" versions. It's
> simply absolutely and purely wrong. I will note that we currently have
> not a single user or strscpy_pad() in the whole kernel outside of the
> testing code.
> 
> And yes, we actually *do* have real and present cases of "source and
> destination have different sizes". They aren't common, but they do
> exist.
> 
> So I'm putting my foot down on yet another broken string copy
> interface from people who do not understand this fundamental issue.

I think you are mistaken about the stracpy limits as
the only limit is not the source size but the dest.

Why should the source be size limited?

btw: I also think str.cpy_pad is horrible.