From: NeilBrown <neilb@suse.de>
To: Fox Chen <foxhlchen@gmail.com>
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: Re: [PATCH v2 08/12] docs: path-lookup: update i_op->put_link and cookie description
Date: Mon, 19 Apr 2021 11:37:21 +1000 [thread overview]
Message-ID: <87y2df12cu.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20210316054727.25655-9-foxhlchen@gmail.com>
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On Tue, Mar 16 2021, Fox Chen wrote:
> 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 e6b6c43ff0f6..8ab95dd9046e 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,
I'd put a ":", not "," at the end of above line.
> +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
() after function names please, both above and below.
Also: "when VFS want to put the link"
With these changes:
Reviewed-by: NeilBrown <neilb@suse.de>
Thanks,
NeilBrown
> +``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
> --
> 2.30.2
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next prev parent reply other threads:[~2021-04-19 1:37 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-16 5:47 [PATCH v2 00/12] docs: path-lookup: Update pathlookup docs Fox Chen
2021-03-16 5:47 ` [PATCH v2 01/12] docs: path-lookup: update follow_managed() part Fox Chen
2021-04-19 0:52 ` NeilBrown
2021-04-19 2:17 ` Matthew Wilcox
2021-04-19 2:33 ` Fox Chen
2021-04-19 3:25 ` Matthew Wilcox
2021-04-19 3:33 ` Fox Chen
2021-04-19 19:22 ` Jonathan Corbet
2021-04-20 1:12 ` Fox Chen
2021-03-16 5:47 ` [PATCH v2 02/12] docs: path-lookup: update path_to_nameidata() part Fox Chen
2021-04-19 1:00 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 03/12] docs: path-lookup: update path_mountpoint() part Fox Chen
2021-04-19 1:03 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 04/12] docs: path-lookup: update do_last() part Fox Chen
2021-04-19 1:17 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 05/12] docs: path-lookup: remove filename_mountpoint Fox Chen
2021-04-19 1:20 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 06/12] docs: path-lookup: Add macro name to symlink limit description Fox Chen
2021-04-19 1:22 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 07/12] docs: path-lookup: i_op->follow_link replaced with i_op->get_link Fox Chen
2021-04-19 1:28 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 08/12] docs: path-lookup: update i_op->put_link and cookie description Fox Chen
2021-04-19 1:37 ` NeilBrown [this message]
2021-03-16 5:47 ` [PATCH v2 09/12] docs: path-lookup: no get_link() Fox Chen
2021-04-19 1:41 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 10/12] docs: path-lookup: update WALK_GET, WALK_PUT desc Fox Chen
2021-04-19 1:47 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 11/12] docs: path-lookup: update get_link() ->follow_link description Fox Chen
2021-04-19 1:54 ` NeilBrown
2021-03-16 5:47 ` [PATCH v2 12/12] docs: path-lookup: update symlink description Fox Chen
2021-04-19 1:59 ` NeilBrown
2021-04-19 2:34 ` Fox Chen
2021-04-13 21:18 ` [PATCH v2 00/12] docs: path-lookup: Update pathlookup docs Jonathan Corbet
2021-04-13 22:26 ` NeilBrown
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