VFS: delay the dentry name generation on sockets and pipes

[net-next-2.6.git] / Documentation / filesystems / vfs.txt

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index ea271f2d395400b82cd8023db74fed76d878ce06..a47cc819f37bb7f5535afbf2bf720766ae51dfdd 100644 (file)
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -827,7 +827,7 @@ This describes how a filesystem can overload the standard dentry
 operations. Dentries and the dcache are the domain of the VFS and the
 individual filesystem implementations. Device drivers have no business
 here. These methods may be set to NULL, as they are either optional or
-the VFS uses a default. As of kernel 2.6.13, the following members are
+the VFS uses a default. As of kernel 2.6.22, the following members are
 defined:
 
 struct dentry_operations {
@@ -837,6 +837,7 @@ struct dentry_operations {
        int (*d_delete)(struct dentry *);
        void (*d_release)(struct dentry *);
        void (*d_iput)(struct dentry *, struct inode *);
+       char *(*d_dname)(struct dentry *, char *, int);
 };
 
   d_revalidate: called when the VFS needs to revalidate a dentry. This
@@ -859,6 +860,26 @@ struct dentry_operations {
        VFS calls iput(). If you define this method, you must call
        iput() yourself
 
+  d_dname: called when the pathname of a dentry should be generated.
+       Usefull for some pseudo filesystems (sockfs, pipefs, ...) to delay
+       pathname generation. (Instead of doing it when dentry is created,
+       its done only when the path is needed.). Real filesystems probably
+       dont want to use it, because their dentries are present in global
+       dcache hash, so their hash should be an invariant. As no lock is
+       held, d_dname() should not try to modify the dentry itself, unless
+       appropriate SMP safety is used. CAUTION : d_path() logic is quite
+       tricky. The correct way to return for example "Hello" is to put it
+       at the end of the buffer, and returns a pointer to the first char.
+       dynamic_dname() helper function is provided to take care of this.
+
+Example :
+
+static char *pipefs_dname(struct dentry *dent, char *buffer, int buflen)
+{
+       return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
+                               dentry->d_inode->i_ino);
+}
+
 Each dentry has a pointer to its parent dentry, as well as a hash list
 of child dentries. Child dentries are basically like files in a
 directory.