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: fceef393a538134f03b778c5d2519e670269342f Signed-off-by: Fox Chen <foxhlchen@xxxxxxxxx> --- Documentation/filesystems/path-lookup.rst | 31 +++++++---------------- 1 file changed, 9 insertions(+), 22 deletions(-) diff --git a/Documentation/filesystems/path-lookup.rst b/Documentation/filesystems/path-lookup.rst index 0a362849b26f..8572300b5405 100644 --- a/Documentation/filesystems/path-lookup.rst +++ b/Documentation/filesystems/path-lookup.rst @@ -1068,34 +1068,21 @@ 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. + +Finally, 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``. Latter 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 -- 2.30.0
