Add missing documentation for the d_op->d_real() method and d_real()
helper.
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
---
Documentation/filesystems/Locking | 2 ++
Documentation/filesystems/vfs.txt | 19 +++++++++++++++++++
include/linux/dcache.h | 7 +++++++
3 files changed, 28 insertions(+)
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -20,6 +20,7 @@ be able to use diff(1).
char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
struct vfsmount *(*d_automount)(struct path *path);
int (*d_manage)(struct dentry *, bool);
+ struct dentry *(*d_real)(struct dentry *, struct inode *, unsigned int);
locking rules:
rename_lock ->d_lock may block rcu-walk
@@ -34,6 +35,7 @@ d_iput: no no yes no
d_dname: no no no no
d_automount: no no yes no
d_manage: no no yes (ref-walk) maybe
+d_real no no yes no
--------------------------- inode_operations ---------------------------
prototypes:
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -938,6 +938,7 @@ struct dentry_operations {
char *(*d_dname)(struct dentry *, char *, int);
struct vfsmount *(*d_automount)(struct path *);
int (*d_manage)(struct dentry *, bool);
+ struct dentry *(*d_real)(struct dentry *, struct inode *, unsigned int);
};
d_revalidate: called when the VFS needs to revalidate a dentry. This
@@ -1060,6 +1061,24 @@ struct dentry_operations {
This function is only used if DCACHE_MANAGE_TRANSIT is set on the
dentry being transited from.
+ d_real: overlay/union type filesystems implement this method to return one of
+ the underlying dentries hidden by the overlay. It is used in three
+ different modes:
+
+ Called from open it may need to copy-up the file depending on the
+ supplied open flags. This mode is selected with a non-zero flags
+ argument. In this mode the d_real method can return an error.
+
+ Called from file_dentry() it returns the real dentry matching the inode
+ argument. The real dentry may be from a lower layer already copied up,
+ but still referenced from the file. This mode is selected with a
+ non-NULL inode argument. This will always succeed.
+
+ With NULL inode and zero flags the topmost real underlying dentry is
+ returned. This will always succeed.
+
+ This method is never called with both non-NULL inode and non-zero flags.
+
Example :
static char *pipefs_dname(struct dentry *dent, char *buffer, int buflen)
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -554,6 +554,13 @@ static inline struct dentry *d_backing_d
return upper;
}
+/**
+ * d_real - Return the real dentry
+ * @dentry: The dentry to query
+ *
+ * If dentry is on an union/overlay, then return the underlying, real dentry.
+ * Otherwise return the dentry itself.
+ */
static inline struct dentry *d_real(struct dentry *dentry)
{
if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
--
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