VFS: Introduce inode-getting helpers for layered/unioned fs environments

Introduce some function for getting the inode (and also the dentry) in an environment where layered/unioned filesystems are in operation. The problem is that we have places where we need *both* the union dentry and the lower source or workspace inode or dentry available, but we can only have a handle on one of them. Therefore we need to derive the handle to the other from that. The idea is to introduce an extra field in struct dentry that allows the union dentry to refer to and pin the lower dentry. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

VFS: Introduce inode-getting helpers for layered/unioned fs environments
Introduce some function for getting the inode (and also the dentry) in an environment where layered/unioned filesystems are in operation. The problem is that we have places where we need *both* the union dentry and the lower source or workspace inode or dentry available, but we can only have a handle on one of them. Therefore we need to derive the handle to the other from that. The idea is to introduce an extra field in struct dentry that allows the union dentry to refer to and pin the lower dentry. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
David Howells · Al Viro
1 parent ce7b9facdf
Showing 1 changed file with 57 additions and 0 deletions Side-by-side Diff
include/linux/dcache.h
@@ -464,5 +464,62 @@
 {
 	return mult_frac(val, sysctl_vfs_cache_pressure, 100);
 }
+
+/**
+ * d_inode - Get the actual inode of this dentry
+ * @dentry: The dentry to query
+ *
+ * This is the helper normal filesystems should use to get at their own inodes
+ * in their own dentries and ignore the layering superimposed upon them.
+ */
+static inline struct inode *d_inode(const struct dentry *dentry)
+{
+	return dentry->d_inode;
+}
+
+/**
+ * d_inode_rcu - Get the actual inode of this dentry with ACCESS_ONCE()
+ * @dentry: The dentry to query
+ *
+ * This is the helper normal filesystems should use to get at their own inodes
+ * in their own dentries and ignore the layering superimposed upon them.
+ */
+static inline struct inode *d_inode_rcu(const struct dentry *dentry)
+{
+	return ACCESS_ONCE(dentry->d_inode);
+}
+
+/**
+ * d_backing_inode - Get upper or lower inode we should be using
+ * @upper: The upper layer
+ *
+ * This is the helper that should be used to get at the inode that will be used
+ * if this dentry were to be opened as a file.  The inode may be on the upper
+ * dentry or it may be on a lower dentry pinned by the upper.
+ *
+ * Normal filesystems should not use this to access their own inodes.
+ */
+static inline struct inode *d_backing_inode(const struct dentry *upper)
+{
+	struct inode *inode = upper->d_inode;
+
+	return inode;
+}
+
+/**
+ * d_backing_dentry - Get upper or lower dentry we should be using
+ * @upper: The upper layer
+ *
+ * This is the helper that should be used to get the dentry of the inode that
+ * will be used if this dentry were opened as a file.  It may be the upper
+ * dentry or it may be a lower dentry pinned by the upper.
+ *
+ * Normal filesystems should not use this to access their own dentries.
+ */
+static inline struct dentry *d_backing_dentry(struct dentry *upper)
+{
+	return upper;
+}
+
 #endif	/* __LINUX_DCACHE_H */
...	...	@@ -464,5 +464,62 @@
464	464	{
465	465	return mult_frac(val, sysctl_vfs_cache_pressure, 100);
466	466	}
	467	+
	468	+/**
	469	+ * d_inode - Get the actual inode of this dentry
	470	+ * @dentry: The dentry to query
	471	+ *
	472	+ * This is the helper normal filesystems should use to get at their own inodes
	473	+ * in their own dentries and ignore the layering superimposed upon them.
	474	+ */
	475	+static inline struct inode d_inode(const struct dentry dentry)
	476	+{
	477	+ return dentry->d_inode;
	478	+}
	479	+
	480	+/**
	481	+ * d_inode_rcu - Get the actual inode of this dentry with ACCESS_ONCE()
	482	+ * @dentry: The dentry to query
	483	+ *
	484	+ * This is the helper normal filesystems should use to get at their own inodes
	485	+ * in their own dentries and ignore the layering superimposed upon them.
	486	+ */
	487	+static inline struct inode d_inode_rcu(const struct dentry dentry)
	488	+{
	489	+ return ACCESS_ONCE(dentry->d_inode);
	490	+}
	491	+
	492	+/**
	493	+ * d_backing_inode - Get upper or lower inode we should be using
	494	+ * @upper: The upper layer
	495	+ *
	496	+ * This is the helper that should be used to get at the inode that will be used
	497	+ * if this dentry were to be opened as a file. The inode may be on the upper
	498	+ * dentry or it may be on a lower dentry pinned by the upper.
	499	+ *
	500	+ * Normal filesystems should not use this to access their own inodes.
	501	+ */
	502	+static inline struct inode d_backing_inode(const struct dentry upper)
	503	+{
	504	+ struct inode *inode = upper->d_inode;
	505	+
	506	+ return inode;
	507	+}
	508	+
	509	+/**
	510	+ * d_backing_dentry - Get upper or lower dentry we should be using
	511	+ * @upper: The upper layer
	512	+ *
	513	+ * This is the helper that should be used to get the dentry of the inode that
	514	+ * will be used if this dentry were opened as a file. It may be the upper
	515	+ * dentry or it may be a lower dentry pinned by the upper.
	516	+ *
	517	+ * Normal filesystems should not use this to access their own dentries.
	518	+ */
	519	+static inline struct dentry d_backing_dentry(struct dentry upper)
	520	+{
	521	+ return upper;
	522	+}
	523	+
467	524	#endif /* __LINUX_DCACHE_H */