NFS: While the storage container for NFS file handles must be able to

   store 128 bytes, usually NFS servers don't use file handles that
   are more than 32 bytes in size.  This patch creates an efficient
   mechanism for comparing file handles that ignores the unused bytes
   in a file handle.
Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@fys.uio.no>

fs/lockd/svcsubs.c

@@ -67,7 +67,7 @@ nlm_lookup_file(struct svc_rqst *rqstp, struct nlm_file **result,
 	down(&nlm_file_sema);
 
 	for (file = nlm_files[hash]; file; file = file->f_next)
-		if (!memcmp(&file->f_handle, f, sizeof(*f)))
+		if (!nfs_compare_fh(&file->f_handle, f))
 			goto found;
 
 	dprintk("lockd: creating file for (%08x %08x %08x %08x %08x %08x)\n",

fs/nfs/dir.c

@@ -610,7 +610,7 @@ static int nfs_lookup_revalidate(struct dentry * dentry, struct nameidata *nd)
 	verifier = nfs_save_change_attribute(dir);
 	error = nfs_cached_lookup(dir, dentry, &fhandle, &fattr);
 	if (!error) {
-		if (memcmp(NFS_FH(inode), &fhandle, sizeof(struct nfs_fh))!= 0)
+		if (nfs_compare_fh(NFS_FH(inode), &fhandle))
 			goto out_bad;
 		if (nfs_lookup_verify_inode(inode, isopen))
 			goto out_zap_parent;
@@ -623,7 +623,7 @@ static int nfs_lookup_revalidate(struct dentry * dentry, struct nameidata *nd)
 	error = NFS_PROTO(dir)->lookup(dir, &dentry->d_name, &fhandle, &fattr);
 	if (error)
 		goto out_bad;
-	if (memcmp(NFS_FH(inode), &fhandle, sizeof(struct nfs_fh))!= 0)
+	if (nfs_compare_fh(NFS_FH(inode), &fhandle))
 		goto out_bad;
 	if ((error = nfs_refresh_inode(inode, &fattr)) != 0)
 		goto out_bad;

fs/nfs/inode.c

@@ -596,7 +596,7 @@ nfs_find_actor(struct inode *inode, void *opaque)
 
 	if (NFS_FILEID(inode) != fattr->fileid)
 		return 0;
-	if (memcmp(NFS_FH(inode), fh, sizeof(struct nfs_fh)) != 0)
+	if (nfs_compare_fh(NFS_FH(inode), fh))
 		return 0;
 	if (is_bad_inode(inode))
 		return 0;
@@ -1259,7 +1259,7 @@ static int nfs_compare_super(struct super_block *sb, void *data)
 		return 0;
 	if (old->addr.sin_port != server->addr.sin_port)
 		return 0;
-	return !memcmp(&old->fh, &server->fh, sizeof(struct nfs_fh));
+	return !nfs_compare_fh(&old->fh, &server->fh);
 }
 
 static struct super_block *nfs_get_sb(struct file_system_type *fs_type,

include/linux/nfs.h

@@ -8,6 +8,7 @@
 #define _LINUX_NFS_H
 
 #include <linux/sunrpc/msg_prot.h>
+#include <linux/string.h>
 
 #define NFS_PROGRAM	100003
 #define NFS_PORT	2049
@@ -138,6 +139,16 @@ struct nfs_fh {
 	unsigned char		data[NFS_MAXFHSIZE];
 };
 
+/*
+ * Returns a zero iff the size and data fields match.
+ * Checks only "size" bytes in the data field.
+ */
+static inline int nfs_compare_fh(const struct nfs_fh *a, const struct nfs_fh *b)
+{
+	return a->size != b->size || memcmp(a->data, b->data, a->size) != 0;
+}
+
+
 /*
  * This is really a general kernel constant, but since nothing like
  * this is defined in the kernel headers, I have to do it here.