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>

3 files changed, 8 insertions, 8 deletions

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 8f737e76935c..63e821a80987 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -70,7 +70,7 @@ prototypes::
 	const char *(*get_link) (struct dentry *, struct inode *, struct delayed_call *);
 	void (*truncate) (struct inode *);
 	int (*permission) (struct inode *, int, unsigned int);
-	struct posix_acl * (*get_acl)(struct inode *, int, bool);
+	struct posix_acl * (*get_inode_acl)(struct inode *, int, bool);
 	int (*setattr) (struct dentry *, struct iattr *);
 	int (*getattr) (const struct path *, struct kstat *, u32, unsigned int);
 	ssize_t (*listxattr) (struct dentry *, char *, size_t);
@@ -88,9 +88,9 @@ prototypes::
 locking rules:
 	all may block
 
-=============	=============================================
+==============	=============================================
 ops		i_rwsem(inode)
-=============	=============================================
+==============	=============================================
 lookup:		shared
 create:		exclusive
 link:		exclusive (both)
@@ -104,7 +104,7 @@ readlink:	no
 get_link:	no
 setattr:	exclusive
 permission:	no (may not block if called in rcu-walk mode)
-get_acl:	no
+get_inode_acl:	no
 getattr:	no
 listxattr:	no
 fiemap:		no
@@ -113,7 +113,7 @@ atomic_open:	shared (exclusive if O_CREAT is set in open flags)
 tmpfile:	no
 fileattr_get:	no or exclusive
 fileattr_set:	exclusive
-=============	=============================================
+==============	=============================================
 
 
 	Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_rwsem
diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index df0dc37e6f58..d2d684ae7798 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -462,8 +462,8 @@ ERR_PTR(...).
 argument; instead of passing IPERM_FLAG_RCU we add MAY_NOT_BLOCK into mask.
 
 generic_permission() has also lost the check_acl argument; ACL checking
-has been taken to VFS and filesystems need to provide a non-NULL ->i_op->get_acl
-to read an ACL from disk.
+has been taken to VFS and filesystems need to provide a non-NULL
+->i_op->get_inode_acl to read an ACL from disk.
 
 ---
 
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index cbf3088617c7..cebede60db98 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -435,7 +435,7 @@ As of kernel 2.6.22, the following members are defined:
 		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 (*setattr) (struct user_namespace *, struct dentry *, struct iattr *);
 		int (*getattr) (struct user_namespace *, const struct path *, struct kstat *, u32, unsigned int);
 		ssize_t (*listxattr) (struct dentry *, char *, size_t);