From: Fox Chen <foxhlchen@gmail.com>
To: neilb@suse.de
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: [PATCH v3 08/13] docs: path-lookup: update i_op->put_link and cookie description
Date: Thu, 27 May 2021 17:16:13 +0800 [thread overview]
Message-ID: <20210527091618.287093-9-foxhlchen@gmail.com> (raw)
In-Reply-To: <20210527091618.287093-1-foxhlchen@gmail.com>
No inode->put_link operation anymore. We use delayed_call to
deal with link destruction. Cookie has been replaced with
struct delayed_call.
Related commit: commit fceef393a538 ("switch ->get_link() to
delayed_call, kill ->put_link()")
Signed-off-by: Fox Chen <foxhlchen@gmail.com>
---
Documentation/filesystems/path-lookup.rst | 30 ++++++-----------------
1 file changed, 8 insertions(+), 22 deletions(-)
diff --git a/Documentation/filesystems/path-lookup.rst b/Documentation/filesystems/path-lookup.rst
index 4650c6427963..3855809784cf 100644
--- a/Documentation/filesystems/path-lookup.rst
+++ b/Documentation/filesystems/path-lookup.rst
@@ -1066,34 +1066,20 @@ method. This is called both in RCU-walk and REF-walk. In RCU-walk the
RCU-walk. Much like the ``i_op->permission()`` method we
looked at previously, ``->get_link()`` would need to be careful that
all the data structures it references are safe to be accessed while
-holding no counted reference, only the RCU lock. Though getting a
-reference with ``->follow_link()`` is not yet done in RCU-walk mode, the
-code is ready to release the reference when that does happen.
-
-This need to drop the reference to a symlink adds significant
-complexity. It requires a reference to the inode so that the
-``i_op->put_link()`` inode operation can be called. In REF-walk, that
-reference is kept implicitly through a reference to the dentry, so
-keeping the ``struct path`` of the symlink is easiest. For RCU-walk,
-the pointer to the inode is kept separately. To allow switching from
-RCU-walk back to REF-walk in the middle of processing nested symlinks
-we also need the seq number for the dentry so we can confirm that
-switching back was safe.
-
-Finally, when providing a reference to a symlink, the filesystem also
-provides an opaque "cookie" that must be passed to ``->put_link()`` so that it
-knows what to free. This might be the allocated memory area, or a
-pointer to the ``struct page`` in the page cache, or something else
-completely. Only the filesystem knows what it is.
+holding no counted reference, only the RCU lock. A callback
+``struct delayed_called`` will be passed to ``->get_link()``:
+file systems can set their own put_link function and argument through
+``set_delayed_call()``. Later on, when VFS wants to put link, it will call
+``do_delayed_call()`` to invoke that callback function with the argument.
In order for the reference to each symlink to be dropped when the walk completes,
whether in RCU-walk or REF-walk, the symlink stack needs to contain,
along with the path remnants:
-- the ``struct path`` to provide a reference to the inode in REF-walk
-- the ``struct inode *`` to provide a reference to the inode in RCU-walk
+- the ``struct path`` to provide a reference to the previous path
+- the ``const char *`` to provide a reference to the to previous name
- the ``seq`` to allow the path to be safely switched from RCU-walk to REF-walk
-- the ``cookie`` that tells ``->put_path()`` what to put.
+- the ``struct delayed_call`` for later invocation.
This means that each entry in the symlink stack needs to hold five
pointers and an integer instead of just one pointer (the path
--
2.31.1
next prev parent reply other threads:[~2021-05-27 9:17 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-27 9:16 [PATCH v3 00/13] docs: path-lookup: Update pathlookup docs Fox Chen
2021-05-27 9:16 ` [PATCH v3 01/13] docs: path-lookup: update follow_managed() part Fox Chen
2021-05-27 9:16 ` [PATCH v3 02/13] docs: path-lookup: update path_to_nameidata() part Fox Chen
2021-05-27 9:16 ` [PATCH v3 03/13] docs: path-lookup: update path_mountpoint() part Fox Chen
2021-05-27 9:16 ` [PATCH v3 04/13] docs: path-lookup: update do_last() part Fox Chen
2021-05-27 9:16 ` [PATCH v3 05/13] docs: path-lookup: remove filename_mountpoint Fox Chen
2021-05-27 9:16 ` [PATCH v3 06/13] docs: path-lookup: Add macro name to symlink limit description Fox Chen
2021-05-27 9:16 ` [PATCH v3 07/13] docs: path-lookup: i_op->follow_link replaced with i_op->get_link Fox Chen
2021-05-27 9:16 ` Fox Chen [this message]
2021-05-27 9:16 ` [PATCH v3 09/13] docs: path-lookup: no get_link() Fox Chen
2021-05-27 9:16 ` [PATCH v3 10/13] docs: path-lookup: update WALK_GET, WALK_PUT desc Fox Chen
2021-06-17 22:31 ` NeilBrown
2021-05-27 9:16 ` [PATCH v3 11/13] docs: path-lookup: update get_link() ->follow_link description Fox Chen
2021-05-27 9:16 ` [PATCH v3 12/13] docs: path-lookup: update symlink description Fox Chen
2021-05-27 9:16 ` [PATCH v3 13/13] docs: path-lookup: use bare function() rather than literals Fox Chen
2021-06-17 22:35 ` [PATCH v3 00/13] docs: path-lookup: Update pathlookup docs NeilBrown
2021-06-18 1:00 ` Fox Chen
2021-06-18 17:39 ` Jonathan Corbet
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