linux-kernel - RE: [PATCH v2 1/4] fs: introduce helper d_path

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Date:   Thu, 24 Jun 2021 05:48:32 +0000
From:   Justin He <Justin.He@....com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Eric Biggers <ebiggers@...gle.com>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>, nd <nd@....com>
Subject: RE: [PATCH v2 1/4] fs: introduce helper d_path_unsafe()

Hi Andy

> -----Original Message-----
> From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Sent: Wednesday, June 23, 2021 5:11 PM
> To: Justin He <Justin.He@....com>
> Cc: Petr Mladek <pmladek@...e.com>; Steven Rostedt <rostedt@...dmis.org>;
> Sergey Senozhatsky <senozhatsky@...omium.org>; Rasmus Villemoes
> <linux@...musvillemoes.dk>; Jonathan Corbet <corbet@....net>; Alexander
> Viro <viro@...iv.linux.org.uk>; Linus Torvalds <torvalds@...ux-
> foundation.org>; Peter Zijlstra (Intel) <peterz@...radead.org>; Eric
> Biggers <ebiggers@...gle.com>; Ahmed S. Darwish <a.darwish@...utronix.de>;
> linux-doc@...r.kernel.org; linux-kernel@...r.kernel.org; linux-
> fsdevel@...r.kernel.org; Matthew Wilcox <willy@...radead.org>; Christoph
> Hellwig <hch@...radead.org>; nd <nd@....com>
> Subject: Re: [PATCH v2 1/4] fs: introduce helper d_path_unsafe()
> 
> On Wed, Jun 23, 2021 at 01:50:08PM +0800, Jia He wrote:
> > This helper is similar to d_path() except that it doesn't take any
> > seqlock/spinlock. It is typical for debugging purposes. Besides,
> > an additional return value *prenpend_len* is used to get the full
> > path length of the dentry, ingoring the tail '\0'.
> > the full path length = end - buf - prepend_length - 1.
> >
> > Previously it will skip the prepend_name() loop at once in
> > __prepen_path() when the buffer length is not enough or even negative.
> > prepend_name_with_len() will get the full length of dentry name
> > together with the parent recursively regardless of the buffer length.
> 
> ...
> 
> >  /**
> >   * prepend_name - prepend a pathname in front of current buffer pointer
> > - * @buffer: buffer pointer
> > - * @buflen: allocated length of the buffer
> > - * @name:   name string and length qstr structure
> > + * @p: prepend buffer which contains buffer pointer and allocated length
> > + * @name: name string and length qstr structure
> >   *
> >   * With RCU path tracing, it may race with d_move(). Use READ_ONCE() to
> >   * make sure that either the old or the new name pointer and length are
> 
> This should be separate patch. You are sending new version too fast...
> Instead of speeding up it will slow down the review process.

Okay, sorry about sending the new version too fast.
I will slow it down and check carefully before sending out.
> 
> ...
> 
> > +	const char *dname = smp_load_acquire(&name->name); /* ^^^ */
> 
> I have commented on the comment here. What does it mean for mere reader?
> 

Do you suggest making the comment "/* ^^^ */" more clear?
It is detailed already in prepend_name_with_len()'s comments:
> * Load acquire is needed to make sure that we see that terminating NUL,
> * which is similar to prepend_name().

Or do you suggest removing the smp_load_acquire()?

> > +	int dlen = READ_ONCE(name->len);
> > +	char *s;
> > +	int last_len = p->len;
> 
> Reversed xmas tree order, please.
> 
> The rule of thumb is when you have gotten a comment against a piece of code,
> try to fix all similar places at once.

Sorry, I misunderstood it, will change it with reverse xmas tree order.

--
Cheers,
Justin (Jia He)