linux-kernel - Re: [PATCH v2 12/12] docs: path-lookup: update symlink description

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Message-ID: <87mttv11bd.fsf@notabene.neil.brown.name>
Date:   Mon, 19 Apr 2021 11:59:50 +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 12/12] docs: path-lookup: update symlink description

On Tue, Mar 16 2021, Fox Chen wrote:

> instead of lookup_real()/vfs_create(), i_op->lookup() and
> i_op->create() will be called directly.
>
> update vfs_open() logic
>
> should_follow_link is merged into lookup_last() or open_last_lookup()
> which returns symlink name instead of an integer.
>
> 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 eef6e9f68fba..adbc714740c2 100644
> --- a/Documentation/filesystems/path-lookup.rst
> +++ b/Documentation/filesystems/path-lookup.rst
> @@ -1202,16 +1202,15 @@ the code.
>     it.  If the file was found in the dcache, then ``vfs_open()`` is used for
>     this.  If not, then ``lookup_open()`` will either call ``atomic_open()`` (if
>     the filesystem provides it) to combine the final lookup with the open, or
> -   will perform the separate ``lookup_real()`` and ``vfs_create()`` steps
> +   will perform the separate ``i_op->lookup()`` and ``i_op->create()`` steps
>     directly.  In the later case the actual "open" of this newly found or
>     created file will be performed by ``vfs_open()``, just as if the name
>     were found in the dcache.
>  
>  2. ``vfs_open()`` can fail with ``-EOPENSTALE`` if the cached information
> -   wasn't quite current enough.  Rather than restarting the lookup from
> -   the top with ``LOOKUP_REVAL`` set, ``lookup_open()`` is called instead,
> -   giving the filesystem a chance to resolve small inconsistencies.
> -   If that doesn't work, only then is the lookup restarted from the top.
> +   wasn't quite current enough.  If it's in RCU-walk -ECHILD will be returned
> +   otherwise will return -ESTALE.  When -ESTALE is returned, the caller may

"otherwise -ESTALE is returned".
If you don't like repeating "is returned", then maybe:
  "... -ECHILD will be returned, otherwise the result is -ESTALE".


> +   retry with LOOKUP_REVAL flag set.
>  
>  3. An open with O_CREAT **does** follow a symlink in the final component,
>     unlike other creation system calls (like ``mkdir``).  So the sequence::
> @@ -1221,8 +1220,8 @@ the code.
>  
>     will create a file called ``/tmp/bar``.  This is not permitted if
>     ``O_EXCL`` is set but otherwise is handled for an O_CREAT open much
> -   like for a non-creating open: ``should_follow_link()`` returns ``1``, and
> -   so does ``do_last()`` so that ``trailing_symlink()`` gets called and the
> +   like for a non-creating open: ``lookup_last()`` or ``open_last_lookup()``
> +   returns a non ``Null`` value, and ``link_path_walk()`` gets called and the

"NULL", not "Null".

This those changes,
 Reviewed-by: NeilBrown <neilb@...e.de>

Thanks for a lot of all these improvements!! and apologies for the delay
in the review.

Thanks,
NeilBrown


>     open process continues on the symlink that was found.
>  
>  Updating the access time
> -- 
> 2.30.2

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