RE: [PATCH 08/14] d_path: make prepend_name() boolean

[Justin He <Justin.He@arm.com>]

Hi Al

> -----Original Message-----
> From: Al Viro <viro@ftp.linux.org.uk> On Behalf Of Al Viro
> Sent: Wednesday, May 19, 2021 8:49 AM
> To: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Justin He <Justin.He@arm.com>; Petr Mladek <pmladek@suse.com>; Steven
> Rostedt <rostedt@goodmis.org>; Sergey Senozhatsky
> <senozhatsky@chromium.org>; Andy Shevchenko
> <andriy.shevchenko@linux.intel.com>; Rasmus Villemoes
> <linux@rasmusvillemoes.dk>; Jonathan Corbet <corbet@lwn.net>; Heiko
> Carstens <hca@linux.ibm.com>; Vasily Gorbik <gor@linux.ibm.com>; Christian
> Borntraeger <borntraeger@de.ibm.com>; Eric W . Biederman
> <ebiederm@xmission.com>; Darrick J. Wong <darrick.wong@oracle.com>; Peter
> Zijlstra (Intel) <peterz@infradead.org>; Ira Weiny <ira.weiny@intel.com>;
> Eric Biggers <ebiggers@google.com>; Ahmed S. Darwish
> <a.darwish@linutronix.de>; open list:DOCUMENTATION <linux-
> doc@vger.kernel.org>; Linux Kernel Mailing List <linux-
> kernel@vger.kernel.org>; linux-s390 <linux-s390@vger.kernel.org>; linux-
> fsdevel <linux-fsdevel@vger.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@zeniv.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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