docs: filesystems: vfs: actualize struct super_operations description

Added/updated descriptions for super_operations:
- free_inode method
- evict_inode method
- freeze_super/thaw_super method
- show_{devname,path,stats} procfs-related methods
- get_dquots method

Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20230313130718.253708-3-aleksandr.mikhalitsyn@canonical.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 59 insertions, 15 deletions

diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 120c42804689..769be5230210 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -245,33 +245,42 @@ struct super_operations
 -----------------------
 
 This describes how the VFS can manipulate the superblock of your
-filesystem.  As of kernel 2.6.22, the following members are defined:
+filesystem.  The following members are defined:
 
 .. code-block:: c
 
 	struct super_operations {
 		struct inode *(*alloc_inode)(struct super_block *sb);
 		void (*destroy_inode)(struct inode *);
+		void (*free_inode)(struct inode *);
 
 		void (*dirty_inode) (struct inode *, int flags);
-		int (*write_inode) (struct inode *, int);
-		void (*drop_inode) (struct inode *);
-		void (*delete_inode) (struct inode *);
+		int (*write_inode) (struct inode *, struct writeback_control *wbc);
+		int (*drop_inode) (struct inode *);
+		void (*evict_inode) (struct inode *);
 		void (*put_super) (struct super_block *);
 		int (*sync_fs)(struct super_block *sb, int wait);
+		int (*freeze_super) (struct super_block *);
 		int (*freeze_fs) (struct super_block *);
+		int (*thaw_super) (struct super_block *);
 		int (*unfreeze_fs) (struct super_block *);
 		int (*statfs) (struct dentry *, struct kstatfs *);
 		int (*remount_fs) (struct super_block *, int *, char *);
-		void (*clear_inode) (struct inode *);
 		void (*umount_begin) (struct super_block *);
 
 		int (*show_options)(struct seq_file *, struct dentry *);
+		int (*show_devname)(struct seq_file *, struct dentry *);
+		int (*show_path)(struct seq_file *, struct dentry *);
+		int (*show_stats)(struct seq_file *, struct dentry *);
 
 		ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
 		ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
-		int (*nr_cached_objects)(struct super_block *);
-		void (*free_cached_objects)(struct super_block *, int);
+		struct dquot **(*get_dquots)(struct inode *);
+
+		long (*nr_cached_objects)(struct super_block *,
+					struct shrink_control *);
+		long (*free_cached_objects)(struct super_block *,
+					struct shrink_control *);
 	};
 
 All methods are called without any locks being held, unless otherwise
@@ -292,6 +301,11 @@ or bottom half).
 	->alloc_inode was defined and simply undoes anything done by
 	->alloc_inode.
 
+``free_inode``
+	this method is called from RCU callback. If you use call_rcu()
+	in ->destroy_inode to free 'struct inode' memory, then it's
+	better to release memory in this method.
+
 ``dirty_inode``
 	this method is called by the VFS when an inode is marked dirty.
 	This is specifically for the inode itself being marked dirty,
@@ -319,8 +333,12 @@ or bottom half).
 	practice of using "force_delete" in the put_inode() case, but
 	does not have the races that the "force_delete()" approach had.
 
-``delete_inode``
-	called when the VFS wants to delete an inode
+``evict_inode``
+	called when the VFS wants to evict an inode. Caller does
+	*not* evict the pagecache or inode-associated metadata buffers;
+	the method has to use truncate_inode_pages_final() to get rid
+	of those. Caller makes sure async writeback cannot be running for
+	the inode while (or after) ->evict_inode() is called. Optional.
 
 ``put_super``
 	called when the VFS wishes to free the superblock
@@ -331,14 +349,25 @@ or bottom half).
 	superblock.  The second parameter indicates whether the method
 	should wait until the write out has been completed.  Optional.
 
+``freeze_super``
+	Called instead of ->freeze_fs callback if provided.
+	Main difference is that ->freeze_super is called without taking
+	down_write(&sb->s_umount). If filesystem implements it and wants
+	->freeze_fs to be called too, then it has to call ->freeze_fs
+	explicitly from this callback. Optional.
+
 ``freeze_fs``
 	called when VFS is locking a filesystem and forcing it into a
 	consistent state.  This method is currently used by the Logical
-	Volume Manager (LVM).
+	Volume Manager (LVM) and ioctl(FIFREEZE). Optional.
+
+``thaw_super``
+	called when VFS is unlocking a filesystem and making it writable
+	again after ->freeze_super. Optional.
 
 ``unfreeze_fs``
 	called when VFS is unlocking a filesystem and making it writable
-	again.
+	again after ->freeze_fs. Optional.
 
 ``statfs``
 	called when the VFS needs to get filesystem statistics.
@@ -347,22 +376,37 @@ or bottom half).
 	called when the filesystem is remounted.  This is called with
 	the kernel lock held
 
-``clear_inode``
-	called then the VFS clears the inode.  Optional
-
 ``umount_begin``
 	called when the VFS is unmounting a filesystem.
 
 ``show_options``
-	called by the VFS to show mount options for /proc/<pid>/mounts.
+	called by the VFS to show mount options for /proc/<pid>/mounts
+	and /proc/<pid>/mountinfo.
 	(see "Mount Options" section)
 
+``show_devname``
+	Optional. Called by the VFS to show device name for
+	/proc/<pid>/{mounts,mountinfo,mountstats}. If not provided then
+	'(struct mount).mnt_devname' will be used.
+
+``show_path``
+	Optional. Called by the VFS (for /proc/<pid>/mountinfo) to show
+	the mount root dentry path relative to the filesystem root.
+
+``show_stats``
+	Optional. Called by the VFS (for /proc/<pid>/mountstats) to show
+	filesystem-specific mount statistics.
+
 ``quota_read``
 	called by the VFS to read from filesystem quota file.
 
 ``quota_write``
 	called by the VFS to write to filesystem quota file.
 
+``get_dquots``
+	called by quota to get 'struct dquot' array for a particular inode.
+	Optional.
+
 ``nr_cached_objects``
 	called by the sb cache shrinking function for the filesystem to
 	return the number of freeable cached objects it contains.