NFS: Avoid duplicate uncached readdir calls on eof

If we've reached the end of the directory, then cache that information
in the context so that we don't need to do an uncached readdir in order
to rediscover that fact.

Fixes: 794092c5 ("NFS: Do uncached readdir when we're seeking a cookie in an empty page cache")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/dir.c

@@ -80,6 +80,7 @@ static struct nfs_open_dir_context *alloc_nfs_open_dir_context(struct inode *dir
 		ctx->dir_cookie = 0;
 		ctx->dup_cookie = 0;
 		ctx->page_index = 0;
+		ctx->eof = false;
 		spin_lock(&dir->i_lock);
 		if (list_empty(&nfsi->open_files) &&
 		    (nfsi->cache_validity & NFS_INO_DATA_INVAL_DEFER))
@@ -168,6 +169,7 @@ struct nfs_readdir_descriptor {
 	unsigned int	cache_entry_index;
 	signed char duped;
 	bool plus;
+	bool eob;
 	bool eof;
 };
 
@@ -989,7 +991,7 @@ static void nfs_do_filldir(struct nfs_readdir_descriptor *desc,
 		ent = &array->array[i];
 		if (!dir_emit(desc->ctx, ent->name, ent->name_len,
 		    nfs_compat_user_ino64(ent->ino), ent->d_type)) {
-			desc->eof = true;
+			desc->eob = true;
 			break;
 		}
 		memcpy(desc->verf, verf, sizeof(desc->verf));
@@ -1005,7 +1007,7 @@ static void nfs_do_filldir(struct nfs_readdir_descriptor *desc,
 			desc->duped = 1;
 	}
 	if (array->page_is_eof)
-		desc->eof = true;
+		desc->eof = !desc->eob;
 
 	kunmap(desc->page);
 	dfprintk(DIRCACHE, "NFS: nfs_do_filldir() filling ended @ cookie %llu\n",
@@ -1048,7 +1050,7 @@ static int uncached_readdir(struct nfs_readdir_descriptor *desc)
 
 	status = nfs_readdir_xdr_to_array(desc, desc->verf, verf, arrays, sz);
 
-	for (i = 0; !desc->eof && i < sz && arrays[i]; i++) {
+	for (i = 0; !desc->eob && i < sz && arrays[i]; i++) {
 		desc->page = arrays[i];
 		nfs_do_filldir(desc, verf);
 	}
@@ -1107,9 +1109,15 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
 	desc->duped = dir_ctx->duped;
 	page_index = dir_ctx->page_index;
 	desc->attr_gencount = dir_ctx->attr_gencount;
+	desc->eof = dir_ctx->eof;
 	memcpy(desc->verf, dir_ctx->verf, sizeof(desc->verf));
 	spin_unlock(&file->f_lock);
 
+	if (desc->eof) {
+		res = 0;
+		goto out_free;
+	}
+
 	if (test_and_clear_bit(NFS_INO_FORCE_READDIR, &nfsi->flags) &&
 	    list_is_singular(&nfsi->open_files))
 		invalidate_mapping_pages(inode->i_mapping, page_index + 1, -1);
@@ -1143,7 +1151,7 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
 
 		nfs_do_filldir(desc, nfsi->cookieverf);
 		nfs_readdir_page_unlock_and_put_cached(desc);
-	} while (!desc->eof);
+	} while (!desc->eob && !desc->eof);
 
 	spin_lock(&file->f_lock);
 	dir_ctx->dir_cookie = desc->dir_cookie;
@@ -1151,9 +1159,10 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
 	dir_ctx->duped = desc->duped;
 	dir_ctx->attr_gencount = desc->attr_gencount;
 	dir_ctx->page_index = desc->page_index;
+	dir_ctx->eof = desc->eof;
 	memcpy(dir_ctx->verf, desc->verf, sizeof(dir_ctx->verf));
 	spin_unlock(&file->f_lock);
-
+out_free:
 	kfree(desc);
 
 out:
@@ -1195,6 +1204,7 @@ static loff_t nfs_llseek_dir(struct file *filp, loff_t offset, int whence)
 		if (offset == 0)
 			memset(dir_ctx->verf, 0, sizeof(dir_ctx->verf));
 		dir_ctx->duped = 0;
+		dir_ctx->eof = false;
 	}
 	spin_unlock(&filp->f_lock);
 	return offset;

include/linux/nfs_fs.h

@@ -107,6 +107,7 @@ struct nfs_open_dir_context {
 	__u64 dup_cookie;
 	pgoff_t page_index;
 	signed char duped;
+	bool eof;
 };
 
 /*