linux-kernel - RE: [PATCH 08/14] d_path: make prepend

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Message-ID: <AM6PR08MB4376607691168C132AB2F558F72A9@AM6PR08MB4376.eurprd08.prod.outlook.com>
Date:   Thu, 20 May 2021 09:12:34 +0000
From:   Justin He <Justin.He@....com>
To:     Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jonathan Corbet <corbet@....net>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Eric Biggers <ebiggers@...gle.com>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: RE: [PATCH 08/14] d_path: make prepend_name() boolean

Hi Al

> -----Original Message-----
> From: Al Viro <viro@....linux.org.uk> On Behalf Of Al Viro
> Sent: Wednesday, May 19, 2021 8:49 AM
> To: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Justin He <Justin.He@....com>; Petr Mladek <pmladek@...e.com>; Steven
> Rostedt <rostedt@...dmis.org>; Sergey Senozhatsky
> <senozhatsky@...omium.org>; Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com>; Rasmus Villemoes
> <linux@...musvillemoes.dk>; Jonathan Corbet <corbet@....net>; Heiko
> Carstens <hca@...ux.ibm.com>; Vasily Gorbik <gor@...ux.ibm.com>; Christian
> Borntraeger <borntraeger@...ibm.com>; Eric W . Biederman
> <ebiederm@...ssion.com>; Darrick J. Wong <darrick.wong@...cle.com>; Peter
> Zijlstra (Intel) <peterz@...radead.org>; Ira Weiny <ira.weiny@...el.com>;
> Eric Biggers <ebiggers@...gle.com>; Ahmed S. Darwish
> <a.darwish@...utronix.de>; open list:DOCUMENTATION <linux-
> doc@...r.kernel.org>; Linux Kernel Mailing List <linux-
> kernel@...r.kernel.org>; linux-s390 <linux-s390@...r.kernel.org>; linux-
> fsdevel <linux-fsdevel@...r.kernel.org>
> Subject: [PATCH 08/14] d_path: make prepend_name() boolean
>
> It returns only 0 or -ENAMETOOLONG and both callers only check if
> the result is negative.  Might as well return true on success and
> false on failure...
>
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
>  fs/d_path.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/fs/d_path.c b/fs/d_path.c
> index 327cc3744554..83db83446afd 100644
> --- a/fs/d_path.c
> +++ b/fs/d_path.c
> @@ -34,15 +34,15 @@ static void prepend(char **buffer, int *buflen, const
> char *str, int namelen)
>   *
>   * Load acquire is needed to make sure that we see that terminating NUL.
>   */
> -static int prepend_name(char **buffer, int *buflen, const struct qstr
> *name)
> +static bool prepend_name(char **buffer, int *buflen, const struct qstr
> *name)
>  {
>       const char *dname = smp_load_acquire(&name->name); /* ^^^ */
>       u32 dlen = READ_ONCE(name->len);
>       char *p;
>
>       *buflen -= dlen + 1;
> -     if (*buflen < 0)
> -             return -ENAMETOOLONG;
> +     if (unlikely(*buflen < 0))
> +             return false;

I don't object to this patch itself.
Just wonder whether we need to relax the check condition of "*buflen < 0" ?

Given that in vsnprintf code path, sometimes the *buflen is < 0.

Please see https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/vsprintf.c#n2698

--
Cheers,

Justin (Jia He)
>       p = *buffer -= dlen + 1;
>       *p++ = '/';
>       while (dlen--) {
> @@ -51,7 +51,7 @@ static int prepend_name(char **buffer, int *buflen, const
> struct qstr *name)
>                       break;
>               *p++ = c;
>       }
> -     return 0;
> +     return true;
>  }
>
>  /**
> @@ -127,7 +127,7 @@ static int prepend_path(const struct path *path,
>               }
>               parent = dentry->d_parent;
>               prefetch(parent);
> -             if (unlikely(prepend_name(&bptr, &blen, &dentry->d_name) < 0))
> +             if (!prepend_name(&bptr, &blen, &dentry->d_name))
>                       break;
>
>               dentry = parent;
> @@ -305,7 +305,7 @@ static char *__dentry_path(const struct dentry *d, char
> *p, int buflen)
>               const struct dentry *parent = dentry->d_parent;
>
>               prefetch(parent);
> -             if (unlikely(prepend_name(&end, &len, &dentry->d_name) < 0))
> +             if (!prepend_name(&end, &len, &dentry->d_name))
>                       break;
>
>               dentry = parent;
> --
> 2.11.0

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