RE: [PATCH v5 1/4] fs: introduce helper d_path_unsafe()

[Justin He]

Hi Andy

> -----Original Message-----
> From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Sent: Tuesday, June 22, 2021 10:37 PM
> To: Justin He <Justin.He@xxxxxxx>
> Cc: Petr Mladek <pmladek@xxxxxxxx>; Steven Rostedt <rostedt@xxxxxxxxxxx>;
> Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>; Rasmus Villemoes
> <linux@xxxxxxxxxxxxxxxxxx>; Jonathan Corbet <corbet@xxxxxxx>; Alexander
> Viro <viro@xxxxxxxxxxxxxxxxxx>; Linus Torvalds <torvalds@linux-
> foundation.org>; Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>; Eric
> Biggers <ebiggers@xxxxxxxxxx>; Ahmed S. Darwish <a.darwish@xxxxxxxxxxxxx>;
> linux-doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> fsdevel@xxxxxxxxxxxxxxx; Matthew Wilcox <willy@xxxxxxxxxxxxx>; Christoph
> Hellwig <hch@xxxxxxxxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [PATCH v5 1/4] fs: introduce helper d_path_unsafe()
> 
> On Tue, Jun 22, 2021 at 10:06:31PM +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
> 
> Missed period at the end of sentence.
> 

Okay
> > 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.
> 
> > If someone invokes snprintf() with small but positive space,
> > prepend_name_with_len() moves and copies the string partially.
> >
> > More than that, kasprintf() will pass NULL _buf_ and _end_ as the
> > parameters. Hence return at the very beginning with false in this case.
> 
> These two paragraphs are talking about printf() interface, while patch has
> nothing to do with it. Please, rephrase in a way that it doesn't refer to
> the
> particular callers. Better to mention them in the corresponding printf()
> patch(es).
> 

Okay
> ...
> 
> >   * prepend_name - prepend a pathname in front of current buffer pointer
> > - * @buffer: buffer pointer
> > - * @buflen: allocated length of the buffer
> > + * @p: prepend buffer which contains buffer pointer and allocated length
> 
> >   * @name:   name string and length qstr structure
> 
> Indentation issue btw, can be fixed in the same patch.

Okay
> 
> >   *
> >   * With RCU path tracing, it may race with d_move(). Use READ_ONCE() to
> 
> Shouldn't this be a separate change with corresponding Fixes tag?

Sorry, I don't quite understand here.
What do you want to fix?

> 
> ...
> 
> > +/**
> > + * d_path_unsafe - return the full path of a dentry without taking
> > + * any seqlock/spinlock. This helper is typical for debugging purposes.
> 
> Seems you ignored my comment, or forget to test, or compile test with
> kernel
> doc validator enabled doesn't show any issues. If it's the latter, we have
> to
> fix kernel doc validator.
> 
> TL;DR: describe parameters as well.
> 

My bad. Apologize for that.
> > + */
> 
> ...
> 
> > +	struct path root;
> > +	struct mount *mnt = real_mount(path->mnt);
> > +	DECLARE_BUFFER(b, buf, buflen);
> 
> Can wee keep this in reversed xmas tree order?

Sure 😊


--
Cheers,
Justin (Jia He)