linux-kernel - RE: [PATCH 06/14] d_path: don't bother with return value of prepend()

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Date:   Thu, 24 Jun 2021 06:13:24 +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 06/14] d_path: don't bother with return value of prepend()



> -----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 06/14] d_path: don't bother with return value of prepend()
>
> Only simple_dname() checks it, and there we can simply do those
> calls and check for overflow (by looking of negative buflen)
> in the end.
>
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>

Reviewed-by: Jia He <justin.he@....com>

--
Cheers,
Justin (Jia He)
> ---
>  fs/d_path.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/fs/d_path.c b/fs/d_path.c
> index 311d43287572..72b8087aaf9c 100644
> --- a/fs/d_path.c
> +++ b/fs/d_path.c
> @@ -8,14 +8,13 @@
>  #include <linux/prefetch.h>
>  #include "mount.h"
>
> -static int prepend(char **buffer, int *buflen, const char *str, int
> namelen)
> +static void prepend(char **buffer, int *buflen, const char *str, int
> namelen)
>  {
>       *buflen -= namelen;
> -     if (*buflen < 0)
> -             return -ENAMETOOLONG;
> -     *buffer -= namelen;
> -     memcpy(*buffer, str, namelen);
> -     return 0;
> +     if (likely(*buflen >= 0)) {
> +             *buffer -= namelen;
> +             memcpy(*buffer, str, namelen);
> +     }
>  }
>
>  /**
> @@ -298,11 +297,10 @@ char *simple_dname(struct dentry *dentry, char
> *buffer, int buflen)
>  {
>       char *end = buffer + buflen;
>       /* these dentries are never renamed, so d_lock is not needed */
> -     if (prepend(&end, &buflen, " (deleted)", 11) ||
> -         prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len)
> ||
> -         prepend(&end, &buflen, "/", 1))
> -             end = ERR_PTR(-ENAMETOOLONG);
> -     return end;
> +     prepend(&end, &buflen, " (deleted)", 11);
> +     prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len);
> +     prepend(&end, &buflen, "/", 1);
> +     return buflen >= 0 ? end : ERR_PTR(-ENAMETOOLONG);
>  }
>
>  /*
> --
> 2.11.0

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