linux-kernel - Re: [PATCH RFCv2 2/3] lib/vsprintf.c: make %pD print full path for file

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Message-ID: <39f599a7-9175-f220-3803-b1920ddb8d40@rasmusvillemoes.dk>
Date:   Tue, 1 Jun 2021 21:01:45 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Matthew Wilcox <willy@...radead.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Justin He <Justin.He@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Luca Coelho <luciano.coelho@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Johannes Berg <johannes.berg@...el.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH RFCv2 2/3] lib/vsprintf.c: make %pD print full path for
 file

On 01/06/2021 19.05, Matthew Wilcox wrote:

> Here's some examples, what do you think makes sense?
> 
> snprintf(buf, 16, "bad file '%pD'\n", q);
> 
> what content do you want buf to have when q is variously:
> 
> 1. /abcd/efgh
> 2. /a/bcdefgh.iso
> 3. /abcdef/gh
> 
> I would argue that
> "bad file ''\n"
> is actually a better string to have than any of (case 2)
> "bad file '/a/bc"
> "bad file 'bcdef"
> "bad file 'h.iso"
> 

Whatever ends up being decided, _please_ document that in
machine-readable and -verifiable form. I.e., update lib/test_printf.c
accordingly.

Currently (and originally) it only tests %pd because %pD is/was
essentially just %pd with an indirection to get the struct dentry* from
a struct file*.

The existing framework is strongly centered around expecting '/a/bc (see
all the logic where we do multiple checks with size 0, size random, size
plenty, and for the random case check that the buffer contents match the
complete output up till the randomly chosen size), so adding tests for
some other semantics would require a bit more juggling.

Not that that should be an argument in favor of that behaviour. But FWIW
that would be my preference.

Rasmus