NFS: Use the 64-bit server readdir cookies when possible

When we're running as a 64-bit architecture and are not running in
32-bit compatibility mode, it is better to use the 64-bit readdir
cookies that supplied by the server. Doing so improves the accuracy
of telldir()/seekdir(), particularly when the directory is changing,
for instance, when doing 'rm -rf'.

We still fall back to using the 32-bit offsets on 32-bit architectures
and when in compatibility mode.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/dir.c

@@ -144,7 +144,6 @@ struct nfs_cache_array {
 	struct nfs_cache_array_entry array[0];
 };
 
-typedef int (*decode_dirent_t)(struct xdr_stream *, struct nfs_entry *, bool);
 typedef struct {
 	struct file	*file;
 	struct page	*page;
@@ -153,7 +152,7 @@ typedef struct {
 	u64		*dir_cookie;
 	u64		last_cookie;
 	loff_t		current_index;
-	decode_dirent_t	decode;
+	loff_t		prev_index;
 
 	unsigned long	dir_verifier;
 	unsigned long	timestamp;
@@ -240,6 +239,25 @@ int nfs_readdir_add_to_array(struct nfs_entry *entry, struct page *page)
 	return ret;
 }
 
+static inline
+int is_32bit_api(void)
+{
+#ifdef CONFIG_COMPAT
+	return in_compat_syscall();
+#else
+	return (BITS_PER_LONG == 32);
+#endif
+}
+
+static
+bool nfs_readdir_use_cookie(const struct file *filp)
+{
+	if ((filp->f_mode & FMODE_32BITHASH) ||
+	    (!(filp->f_mode & FMODE_64BITHASH) && is_32bit_api()))
+		return false;
+	return true;
+}
+
 static
 int nfs_readdir_search_for_pos(struct nfs_cache_array *array, nfs_readdir_descriptor_t *desc)
 {
@@ -289,7 +307,7 @@ int nfs_readdir_search_for_cookie(struct nfs_cache_array *array, nfs_readdir_des
 			    !nfs_readdir_inode_mapping_valid(nfsi)) {
 				ctx->duped = 0;
 				ctx->attr_gencount = nfsi->attr_gencount;
-			} else if (new_pos < desc->ctx->pos) {
+			} else if (new_pos < desc->prev_index) {
 				if (ctx->duped > 0
 				    && ctx->dup_cookie == *desc->dir_cookie) {
 					if (printk_ratelimit()) {
@@ -305,7 +323,11 @@ int nfs_readdir_search_for_cookie(struct nfs_cache_array *array, nfs_readdir_des
 				ctx->dup_cookie = *desc->dir_cookie;
 				ctx->duped = -1;
 			}
-			desc->ctx->pos = new_pos;
+			if (nfs_readdir_use_cookie(desc->file))
+				desc->ctx->pos = *desc->dir_cookie;
+			else
+				desc->ctx->pos = new_pos;
+			desc->prev_index = new_pos;
 			desc->cache_entry_index = i;
 			return 0;
 		}
@@ -376,9 +398,10 @@ int nfs_readdir_xdr_filler(struct page **pages, nfs_readdir_descriptor_t *desc,
 static int xdr_decode(nfs_readdir_descriptor_t *desc,
 		      struct nfs_entry *entry, struct xdr_stream *xdr)
 {
+	struct inode *inode = file_inode(desc->file);
 	int error;
 
-	error = desc->decode(xdr, entry, desc->plus);
+	error = NFS_PROTO(inode)->decode_dirent(xdr, entry, desc->plus);
 	if (error)
 		return error;
 	entry->fattr->time_start = desc->timestamp;
@@ -756,6 +779,7 @@ int readdir_search_pagecache(nfs_readdir_descriptor_t *desc)
 
 	if (desc->page_index == 0) {
 		desc->current_index = 0;
+		desc->prev_index = 0;
 		desc->last_cookie = 0;
 	}
 	do {
@@ -786,11 +810,14 @@ int nfs_do_filldir(nfs_readdir_descriptor_t *desc)
 			desc->eof = true;
 			break;
 		}
-		desc->ctx->pos++;
 		if (i < (array->size-1))
 			*desc->dir_cookie = array->array[i+1].cookie;
 		else
 			*desc->dir_cookie = array->last_cookie;
+		if (nfs_readdir_use_cookie(file))
+			desc->ctx->pos = *desc->dir_cookie;
+		else
+			desc->ctx->pos++;
 		if (ctx->duped != 0)
 			ctx->duped = 1;
 	}
@@ -860,9 +887,14 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
 {
 	struct dentry	*dentry = file_dentry(file);
 	struct inode	*inode = d_inode(dentry);
-	nfs_readdir_descriptor_t my_desc,
-			*desc = &my_desc;
 	struct nfs_open_dir_context *dir_ctx = file->private_data;
+	nfs_readdir_descriptor_t my_desc = {
+		.file = file,
+		.ctx = ctx,
+		.dir_cookie = &dir_ctx->dir_cookie,
+		.plus = nfs_use_readdirplus(inode, ctx),
+	},
+			*desc = &my_desc;
 	int res = 0;
 
 	dfprintk(FILE, "NFS: readdir(%pD2) starting at cookie %llu\n",
@@ -875,14 +907,6 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
 	 * to either find the entry with the appropriate number or
 	 * revalidate the cookie.
 	 */
-	memset(desc, 0, sizeof(*desc));
-
-	desc->file = file;
-	desc->ctx = ctx;
-	desc->dir_cookie = &dir_ctx->dir_cookie;
-	desc->decode = NFS_PROTO(inode)->decode_dirent;
-	desc->plus = nfs_use_readdirplus(inode, ctx);
-
 	if (ctx->pos == 0 || nfs_attribute_cache_expired(inode))
 		res = nfs_revalidate_mapping(inode, file->f_mapping);
 	if (res < 0)
@@ -954,7 +978,10 @@ static loff_t nfs_llseek_dir(struct file *filp, loff_t offset, int whence)
 	}
 	if (offset != filp->f_pos) {
 		filp->f_pos = offset;
-		dir_ctx->dir_cookie = 0;
+		if (nfs_readdir_use_cookie(filp))
+			dir_ctx->dir_cookie = offset;
+		else
+			dir_ctx->dir_cookie = 0;
 		dir_ctx->duped = 0;
 	}
 	inode_unlock(inode);