fs: rename current get acl method

The current way of setting and getting posix acls through the generic
xattr interface is error prone and type unsafe. The vfs needs to
interpret and fixup posix acls before storing or reporting it to
userspace. Various hacks exist to make this work. The code is hard to
understand and difficult to maintain in it's current form. Instead of
making this work by hacking posix acls through xattr handlers we are
building a dedicated posix acl api around the get and set inode
operations. This removes a lot of hackiness and makes the codepaths
easier to maintain. A lot of background can be found in [1].

The current inode operation for getting posix acls takes an inode
argument but various filesystems (e.g., 9p, cifs, overlayfs) need access
to the dentry. In contrast to the ->set_acl() inode operation we cannot
simply extend ->get_acl() to take a dentry argument. The ->get_acl()
inode operation is called from:

acl_permission_check()
-> check_acl()
   -> get_acl()

which is part of generic_permission() which in turn is part of
inode_permission(). Both generic_permission() and inode_permission() are
called in the ->permission() handler of various filesystems (e.g.,
overlayfs). So simply passing a dentry argument to ->get_acl() would
amount to also having to pass a dentry argument to ->permission(). We
should avoid this unnecessary change.

So instead of extending the existing inode operation rename it from
->get_acl() to ->get_inode_acl() and add a ->get_acl() method later that
passes a dentry argument and which filesystems that need access to the
dentry can implement instead of ->get_inode_acl(). Filesystems like cifs
which allow setting and getting posix acls but not using them for
permission checking during lookup can simply not implement
->get_inode_acl().

This is intended to be a non-functional change.

Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1]
Suggested-by/Inspired-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3db0b23c6a5526..2395e1388e2e7f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -560,8 +560,8 @@ struct posix_acl;
 #define ACL_NOT_CACHED ((void *)(-1))
 /*
  * ACL_DONT_CACHE is for stacked filesystems, that rely on underlying fs to
- * cache the ACL.  This also means that ->get_acl() can be called in RCU mode
- * with the LOOKUP_RCU flag.
+ * cache the ACL.  This also means that ->get_inode_acl() can be called in RCU
+ * mode with the LOOKUP_RCU flag.
  */
 #define ACL_DONT_CACHE ((void *)(-3))
 
@@ -2142,7 +2142,7 @@ struct inode_operations {
 	struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int);
 	const char * (*get_link) (struct dentry *, struct inode *, struct delayed_call *);
 	int (*permission) (struct user_namespace *, struct inode *, int);
-	struct posix_acl * (*get_acl)(struct inode *, int, bool);
+	struct posix_acl * (*get_inode_acl)(struct inode *, int, bool);
 
 	int (*readlink) (struct dentry *, char __user *,int);