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Subject[PATCH v3 110/110] update Documentation/filesystems/ regarding the follow_link/put_link changes
Date
From: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
Documentation/filesystems/porting | 17 +++++++++++++++++
Documentation/filesystems/vfs.txt | 18 ++++++++++--------
2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index e69274d..3eae250 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -483,3 +483,20 @@ in your dentry operations instead.
--
[mandatory]
->aio_read/->aio_write are gone. Use ->read_iter/->write_iter.
+---
+[recommended]
+ for embedded ("fast") symlinks just set inode->i_link to wherever the
+ symlink body is and use simple_follow_link() as ->follow_link().
+--
+[mandatory]
+ calling conventions for ->follow_link() have changed. Instead of returning
+ cookie and using nd_set_link() to store the body to traverse, we return
+ the body to traverse and store the cookie using explicit void ** argument.
+ nameidata isn't passed at all - nd_jump_link() doesn't need it and
+ nd_[gs]et_link() is gone.
+--
+[mandatory]
+ calling conventions for ->put_link() have changed. It gets inode instead of
+ dentry, it does not get nameidata at all and it gets called only when cookie
+ is non-NULL. Note that link body isn't available anymore, so if you need it,
+ store it as cookie.
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 542d935..b403b29 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -436,16 +436,18 @@ otherwise noted.

follow_link: called by the VFS to follow a symbolic link to the
inode it points to. Only required if you want to support
- symbolic links. This method returns a void pointer cookie
- that is passed to put_link().
+ symbolic links. This method returns the symlink body
+ to traverse (and possibly resets the current position with
+ nd_jump_link()). If the body won't go away until the inode
+ is gone, nothing else is needed; if it needs to be otherwise
+ pinned, the data needed to release whatever we'd grabbed
+ is to be stored in void * variable passed by address to
+ follow_link() instance.

put_link: called by the VFS to release resources allocated by
- follow_link(). The cookie returned by follow_link() is passed
- to this method as the last parameter. It is used by
- filesystems such as NFS where page cache is not stable
- (i.e. page that was installed when the symbolic link walk
- started might not be in the page cache at the end of the
- walk).
+ follow_link(). The cookie stored by follow_link() is passed
+ to this method as the last parameter; only called when
+ cookie isn't NULL.

permission: called by the VFS to check for access rights on a POSIX-like
filesystem.
--
2.1.4


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