linux-kernel - Re: [PATCH 01/12] docs: path-lookup: update follow

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Date:   Thu, 28 Jan 2021 14:20:59 +1100
From:   NeilBrown <neilb@...e.de>
To:     Fox Chen <foxhlchen@...il.com>, corbet@....net,
        vegard.nossum@...cle.com, viro@...iv.linux.org.uk,
        rdunlap@...radead.org, grandmaster@...klimov.de
Cc:     Fox Chen <foxhlchen@...il.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/12] docs: path-lookup: update follow_managed() part

On Tue, Jan 26 2021, Fox Chen wrote:

> No follow_managed() anymore, handle_mounts(),
> traverse_mounts(), will do the job.
> see commit: 9deed3ebca244663530782631834e706a86a8c8f
>
> Signed-off-by: Fox Chen <foxhlchen@...il.com>
> ---
>  Documentation/filesystems/path-lookup.rst | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/filesystems/path-lookup.rst b/Documentation/filesystems/path-lookup.rst
> index c482e1619e77..e778db767120 100644
> --- a/Documentation/filesystems/path-lookup.rst
> +++ b/Documentation/filesystems/path-lookup.rst
> @@ -448,8 +448,8 @@ described.  If it finds a ``LAST_NORM`` component it first calls
>  filesystem to revalidate the result if it is that sort of filesystem.
>  If that doesn't get a good result, it calls "``lookup_slow()``" which
>  takes ``i_rwsem``, rechecks the cache, and then asks the filesystem
> -to find a definitive answer.  Each of these will call
> -``follow_managed()`` (as described below) to handle any mount points.
> +to find a definitive answer.  In ``step_into()``, ``handle_mount()`` will be 
> +called to handle any mount point.

The text now introduces step_into() without any hint as to why that is
relevant at this point.
It is a bit awkward to explain succinctly because while lookup_fast and
lookup_slow return a dentry which is passed to step_into(), handle_dots()
calls step_into() itself.

This is a general problem with this sort of documentation.  It weaves a
story and when the code changes, you might need to completely re-weave
the story.

I don't have a good suggestion for how to fix this text, but at the
least it needs to be made clear the walk_component() calls step_into(),
either directly or via handle_dots().

>  
>  In the absence of symbolic links, ``walk_component()`` creates a new
>  ``struct path`` containing a counted reference to the new dentry and a
> @@ -536,7 +536,7 @@ tree, but a few notes specifically related to path lookup are in order
>  here.
>  
>  The Linux VFS has a concept of "managed" dentries which is reflected
> -in function names such as "``follow_managed()``".  There are three
> +in function names such as "``traverse_mounts()``".  There are three

Here you've completely broken the story.  Saying

  The VFS has a concept of "managed" dentries which is reflected in
  function names like "traverse_mounts()"

makes no sense at all.
Again, I cannot offer any quick fix.

NeilBrown


>  potentially interesting things about these dentries corresponding
>  to three different flags that might be set in ``dentry->d_flags``:
>  
> -- 
> 2.30.0

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