[PATCH v2 04/12] docs: path-lookup: update do_last() part

Fox Chen
2021-03-16T05:48:57Z

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.

-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