From: NeilBrown <neilb@suse.de>
To: Fox Chen <foxhlchen@gmail.com>
Cc: Fox Chen <foxhlchen@gmail.com>,
corbet@lwn.net, vegard.nossum@oracle.com,
viro@zeniv.linux.org.uk, rdunlap@infradead.org,
grandmaster@al2klimov.de, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org
Subject: Re: [PATCH v2 04/12] docs: path-lookup: update do_last() part
Date: Mon, 19 Apr 2021 11:17:10 +1000 [thread overview]
Message-ID: <87blab2hux.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20210316054727.25655-5-foxhlchen@gmail.com>
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On Tue, Mar 16 2021, Fox Chen wrote:
> traling_symlink() was merged into lookup_last, do_last().
>
> do_last() has later been split into open_last_lookups()
> and do_open().
>
> see related commit: commit c5971b8c6354 ("take post-lookup
> part of do_last() out of loop")
>
> Signed-off-by: Fox Chen <foxhlchen@gmail.com>
> ---
> Documentation/filesystems/path-lookup.rst | 35 ++++++++++++-----------
> 1 file changed, 18 insertions(+), 17 deletions(-)
>
> diff --git a/Documentation/filesystems/path-lookup.rst b/Documentation/filesystems/path-lookup.rst
> index b6a301b78121..a65cb477d524 100644
> --- a/Documentation/filesystems/path-lookup.rst
> +++ b/Documentation/filesystems/path-lookup.rst
> @@ -495,11 +495,11 @@ This is important when unmounting a filesystem that is inaccessible, such as
> one provided by a dead NFS server.
>
> Finally ``path_openat()`` is used for the ``open()`` system call; it
> -contains, in support functions starting with "``do_last()``", all the
> +contains, in support functions starting with "``open_last_lookups()``", all the
> complexity needed to handle the different subtleties of O_CREAT (with
> or without O_EXCL), final "``/``" characters, and trailing symbolic
> links. We will revisit this in the final part of this series, which
> -focuses on those symbolic links. "``do_last()``" will sometimes, but
> +focuses on those symbolic links. "``open_last_lookups()``" will sometimes, but
> not always, take ``i_rwsem``, depending on what it finds.
>
> Each of these, or the functions which call them, need to be alert to
> @@ -1199,26 +1199,27 @@ symlink.
> This case is handled by the relevant caller of ``link_path_walk()``, such as
> ``path_lookupat()`` using a loop that calls ``link_path_walk()``, and then
> handles the final component. If the final component is a symlink
> -that needs to be followed, then ``trailing_symlink()`` is called to set
> -things up properly and the loop repeats, calling ``link_path_walk()``
> -again. This could loop as many as 40 times if the last component of
> -each symlink is another symlink.
> +that needs to be followed, then ``open_last_lookups()`` is
> +called to set things up properly and the loop repeats, calling
> +``link_path_walk()`` again. This could loop as many as 40 times if the last
> +component of each symlink is another symlink.
>
> The various functions that examine the final component and possibly
> -report that it is a symlink are ``lookup_last()``, ``mountpoint_last()``
> -and ``do_last()``, each of which use the same convention as
> -``walk_component()`` of returning ``1`` if a symlink was found that needs
> -to be followed.
> +report that it is a symlink are ``lookup_last()``, ``open_last_lookups()``
> +, each of which use the same convention as
> +``walk_component()`` of returning ``char *name`` if a symlink was found that
> +needs to be followed.
This para no longer makes sense.
There is only one function that examines the final compoenent:
step_into()
It is called from open_last_lookups() directly and indirectly from
lookup_last() through walk_component().
But saying that here might be duplicating earlier text.
I think the key point in the para is that convention of returning a
'char *name' if a symlink was found. The rest might now be redundant.
I think this needs a larger revision.
Thanks,
NeilBrown
>
> -Of these, ``do_last()`` is the most interesting as it is used for
> -opening a file. Part of ``do_last()`` runs with ``i_rwsem`` held and this
> -part is in a separate function: ``lookup_open()``.
> +Of these, ``open_last_lookups()`` is the most interesting as it works in tandem
> +with ``do_open()`` for opening a file. Part of ``open_last_lookups()`` runs
> +with ``i_rwsem`` held and this part is in a separate function: ``lookup_open()``.
>
> -Explaining ``do_last()`` completely is beyond the scope of this article,
> -but a few highlights should help those interested in exploring the
> -code.
> +Explaining ``open_last_lookups()`` and ``do_open()`` completely is beyond the scope
> +of this article, but a few highlights should help those interested in exploring
> +the code.
>
> -1. Rather than just finding the target file, ``do_last()`` needs to open
> +1. Rather than just finding the target file, ``do_open()`` is used after
> + ``open_last_lookup()`` to open
> 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
> --
> 2.30.2
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next prev parent reply other threads:[~2021-04-19 1:17 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-16 5:47 [PATCH v2 00/12] docs: path-lookup: Update pathlookup docs Fox Chen
2021-03-16 5:47 ` [PATCH v2 01/12] docs: path-lookup: update follow_managed() part Fox Chen
2021-04-19 0:52 ` NeilBrown
2021-04-19 2:17 ` Matthew Wilcox
2021-04-19 2:33 ` Fox Chen
2021-04-19 3:25 ` Matthew Wilcox
2021-04-19 3:33 ` Fox Chen
2021-04-19 19:22 ` Jonathan Corbet
2021-04-20 1:12 ` Fox Chen
2021-03-16 5:47 ` [PATCH v2 02/12] docs: path-lookup: update path_to_nameidata() part Fox Chen
2021-04-19 1:00 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 03/12] docs: path-lookup: update path_mountpoint() part Fox Chen
2021-04-19 1:03 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 04/12] docs: path-lookup: update do_last() part Fox Chen
2021-04-19 1:17 ` NeilBrown [this message]
2021-03-16 5:47 ` [PATCH v2 05/12] docs: path-lookup: remove filename_mountpoint Fox Chen
2021-04-19 1:20 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 06/12] docs: path-lookup: Add macro name to symlink limit description Fox Chen
2021-04-19 1:22 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 07/12] docs: path-lookup: i_op->follow_link replaced with i_op->get_link Fox Chen
2021-04-19 1:28 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 08/12] docs: path-lookup: update i_op->put_link and cookie description Fox Chen
2021-04-19 1:37 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 09/12] docs: path-lookup: no get_link() Fox Chen
2021-04-19 1:41 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 10/12] docs: path-lookup: update WALK_GET, WALK_PUT desc Fox Chen
2021-04-19 1:47 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 11/12] docs: path-lookup: update get_link() ->follow_link description Fox Chen
2021-04-19 1:54 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 12/12] docs: path-lookup: update symlink description Fox Chen
2021-04-19 1:59 ` NeilBrown
2021-04-19 2:34 ` Fox Chen
2021-04-13 21:18 ` [PATCH v2 00/12] docs: path-lookup: Update pathlookup docs Jonathan Corbet
2021-04-13 22:26 ` NeilBrown
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