linux-kernel - Re: [GIT PULL] iomap: new code for 5.13-rc1

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Message-ID: <1de23de2-12a9-2b13-3b86-9fe4102fdc0c@rasmusvillemoes.dk>
Date:   Wed, 28 Apr 2021 09:38:10 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>
Cc:     "Darrick J. Wong" <djwong@...nel.org>, Jia He <justin.he@....com>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Dave Chinner <david@...morbit.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Eric Sandeen <sandeen@...deen.net>
Subject: Re: [GIT PULL] iomap: new code for 5.13-rc1

On 28/04/2021 09.14, Linus Torvalds wrote:
So let me just quote that first reply of mine, because you seem to not
> have seen it:
> 
>> We have '%pD' for printing a filename. It may not be perfect (by
>> default it only prints one component, you can do "%pD4" to show up to
>> four components), but it should "JustWork(tm)".
>>
>> And if it doesn't, we should fix it.
> 
> I really think %pD4 should be more than good enough. And I think maybe
> we should make plain "%pD" mean "as much of the path that is
> reasonable" rather than "as few components as possible" (ie 1).
> 
> So I don't think "%pD" (or "%pD4") is necessarily perfect, but I think
> it's even worse when people then go and do odd ad-hoc things because
> of some inconvenience in our %pD implementation.
> 
> For example, changing the default to be "show more by default" should
> be as simple as something like the attached.  I do think that would be
> the more natural behavior for %pD - don't limit it unnecessarily by
> default, but for somebody who literally just wants to see a maximum of
> 2 components, using '%pD2' makes sense.
> 
> (Similarly, changing the limit of 4  components to something slightly
> bigger would be trivial)
> 
> Hmm?
> 
> Grepping for existing users with
> 
>     git grep '%pD[^1-4]'
>
> most of them would probably like a full pathname, and the odd s390
> hmcdrv_dev.c use should just be fixed (it has a hardcoded "/dev/%pD",
> which seems very wrong).

So the patch makes sense to me. If somebody says '%pD5', it would get
capped at 4 instead of being forced down to 1. But note that while that
grep only produces ~36 hits, it also affects %pd, of which there are
~200 without a 2-4 following (including some vsprintf test cases that
would break). So I think one would first have to explicitly support '1',
switch over some users by adding that 1 in their format string
(test_vsprintf in particular), then flip the default for 'no digit
following %p[dD]'.

Rasmus