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

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Message-ID: <AM6PR08MB4376DB8B76EB0563A0FB75D7F73D9@AM6PR08MB4376.eurprd08.prod.outlook.com>
Date:   Wed, 2 Jun 2021 05:47:43 +0000
From:   Justin He <Justin.He@....com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Matthew Wilcox <willy@...radead.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>
CC:     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

Hi Rasmus

> -----Original Message-----
> From: Rasmus Villemoes <linux@...musvillemoes.dk>
> Sent: Wednesday, June 2, 2021 3:02 AM
> 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-
> kernel@...r.kernel.org; linux-wireless@...r.kernel.org;
> netdev@...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*.

Okay, I can add more test_printf cases for '%pD'

>
> 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.
>

Yes, agree.
In other way, if the user:
char* full_path = d_path(...);
snprintf("%s", limited_size, full_path);

He/she will get the inconsistent result if we return "" for '%pD'.

--
Cheers,
Justin (Jia He)

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

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