linux-kernel - Re: [PATCH v2 11/12] docs: path-lookup: update get_link() ->follow

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Date:   Mon, 19 Apr 2021 11:54:54 +1000
From:   NeilBrown <neilb@...e.de>
To:     Fox Chen <foxhlchen@...il.com>
Cc:     Fox Chen <foxhlchen@...il.com>, corbet@....net,
        vegard.nossum@...cle.com, viro@...iv.linux.org.uk,
        rdunlap@...radead.org, grandmaster@...klimov.de,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org
Subject: Re: [PATCH v2 11/12] docs: path-lookup: update get_link()
 ->follow_link description

On Tue, Mar 16 2021, Fox Chen wrote:

> get_link() is merged into pick_link(). i_op->follow_link is
> replaced with i_op->get_link(). get_link() can return ERR_PTR(0)
> which equals NULL.
>
> Signed-off-by: Fox Chen <foxhlchen@...il.com>
> ---
>  Documentation/filesystems/path-lookup.rst | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/filesystems/path-lookup.rst b/Documentation/filesystems/path-lookup.rst
> index abd0153e2415..eef6e9f68fba 100644
> --- a/Documentation/filesystems/path-lookup.rst
> +++ b/Documentation/filesystems/path-lookup.rst
> @@ -1134,10 +1134,10 @@ Symlinks with no final component
>  
>  A pair of special-case symlinks deserve a little further explanation.
>  Both result in a new ``struct path`` (with mount and dentry) being set
> -up in the ``nameidata``, and result in ``get_link()`` returning ``NULL``.
> +up in the ``nameidata``, and result in ``pick_link()`` returning ``NULL``.
>  
>  The more obvious case is a symlink to "``/``".  All symlinks starting
> -with "``/``" are detected in ``get_link()`` which resets the ``nameidata``
> +with "``/``" are detected in ``pick_link()`` which resets the ``nameidata``
>  to point to the effective filesystem root.  If the symlink only
>  contains "``/``" then there is nothing more to do, no components at all,
>  so ``NULL`` is returned to indicate that the symlink can be released and
> @@ -1154,12 +1154,11 @@ something that looks like a symlink.  It is really a reference to the
>  target file, not just the name of it.  When you ``readlink`` these
>  objects you get a name that might refer to the same file - unless it
>  has been unlinked or mounted over.  When ``walk_component()`` follows
> -one of these, the ``->follow_link()`` method in "procfs" doesn't return
> +one of these, the ``->get_link()`` method in "procfs" doesn't return
>  a string name, but instead calls ``nd_jump_link()`` which updates the
> -``nameidata`` in place to point to that target.  ``->follow_link()`` then
> -returns ``NULL``.  Again there is no final component and ``get_link()``
> -reports this by leaving the ``last_type`` field of ``nameidata`` as
> -``LAST_BIND``.
> +``nameidata`` in place to point to that target.  ``->get_link()`` then
> +returns ``0``.  Again there is no final component and ``pick_link()``

Why did you change NULL to 0?  ->get_link returns a pointer.

Without that change:
  Reviewed-by: NeilBrown <neilb@...e.de>

Thanks,
NeilBrown


> +returns NULL.
>  
>  Following the symlink in the final component
>  --------------------------------------------
> -- 
> 2.30.2

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