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author | 2021-05-27 17:16:13 +0800 | |
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committer | 2021-06-18 11:36:08 -0600 | |
commit | 671f73356f6a2aa2fb1bb71f8fdeeba858b6fec6 (patch) | |
tree | f02abd6a303c8a64ce12de6f6a55d9a57f1d0c53 /Documentation/filesystems | |
parent | docs: path-lookup: i_op->follow_link replaced with i_op->get_link (diff) | |
download | linux-671f73356f6a2aa2fb1bb71f8fdeeba858b6fec6.tar.gz linux-671f73356f6a2aa2fb1bb71f8fdeeba858b6fec6.tar.bz2 linux-671f73356f6a2aa2fb1bb71f8fdeeba858b6fec6.zip |
docs: path-lookup: update i_op->put_link and cookie description
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>
Reviewed-by: NeilBrown <neilb@suse.de>
Link: https://lore.kernel.org/r/20210527091618.287093-9-foxhlchen@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/filesystems')
-rw-r--r-- | Documentation/filesystems/path-lookup.rst | 30 |
1 files 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 |