renegade-project/linux-next
2
0
Fork 0
mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-28 07:04:00 +08:00
Code

docs: path-lookup: update do_last() part

Browse Source 
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 c5971b8c63 ("take post-lookup
part of do_last() out of loop")

Signed-off-by: Fox Chen <foxhlchen@gmail.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Link: https://lore.kernel.org/r/20210527091618.287093-5-foxhlchen@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Fox Chen 2021-05-27 17:16:09 +08:00 committed by Jonathan Corbet
parent 8593d2cc8c
commit 71e0a67dc6
1 changed files with 19 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
Documentation/filesystems/path-lookup.rst
View File

@ -495,11 +495,11 @@ This is important when unmounting a filesystem that is inaccessible, such as
one provided by a dead NFS server. one provided by a dead NFS server.
Finally ``path_openat()`` is used for the ``open()`` system call; it 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 complexity needed to handle the different subtleties of O_CREAT (with
or without O_EXCL), final "``/``" characters, and trailing symbolic or without O_EXCL), final "``/``" characters, and trailing symbolic
links. We will revisit this in the final part of this series, which 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. not always, take ``i_rwsem``, depending on what it finds.
Each of these, or the functions which call them, need to be alert to Each of these, or the functions which call them, need to be alert to
@ -1196,29 +1196,26 @@ potentially need to call ``link_path_walk()`` again and again on
successive symlinks until one is found that doesn't point to another successive symlinks until one is found that doesn't point to another
symlink. symlink.
This case is handled by the relevant caller of ``link_path_walk()``, such as This case is handled by relevant callers of ``link_path_walk()``, such as
``path_lookupat()`` using a loop that calls ``link_path_walk()``, and then ``path_lookupat()``, ``path_openat()`` using a loop that calls ``link_path_walk()``,
handles the final component. If the final component is a symlink and then handles the final component by calling ``open_last_lookups()`` or
that needs to be followed, then ``trailing_symlink()`` is called to set ``lookup_last()``. If it is a symlink that needs to be followed,
things up properly and the loop repeats, calling ``link_path_walk()`` ``open_last_lookups()`` or ``lookup_last()`` will set things up properly and
again. This could loop as many as 40 times if the last component of return the path so that the loop repeats, calling
each symlink is another symlink. ``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 Of the various functions that examine the final component,
report that it is a symlink are ``lookup_last()``, ``mountpoint_last()`` ``open_last_lookups()`` is the most interesting as it works in tandem
and ``do_last()``, each of which use the same convention as with ``do_open()`` for opening a file. Part of ``open_last_lookups()`` runs
``walk_component()`` of returning ``1`` if a symlink was found that needs with ``i_rwsem`` held and this part is in a separate function: ``lookup_open()``.
to be followed.
Of these, ``do_last()`` is the most interesting as it is used for Explaining ``open_last_lookups()`` and ``do_open()`` completely is beyond the scope
opening a file. Part of ``do_last()`` runs with ``i_rwsem`` held and this of this article, but a few highlights should help those interested in exploring
part is in a separate function: ``lookup_open()``. the code.
Explaining ``do_last()`` completely is beyond the scope of this article, 1. Rather than just finding the target file, ``do_open()`` is used after
but a few highlights should help those interested in exploring the ``open_last_lookup()`` to open
code.
1. Rather than just finding the target file, ``do_last()`` needs to open
it. If the file was found in the dcache, then ``vfs_open()`` is used for 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 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 the filesystem provides it) to combine the final lookup with the open, or