smb: client: short-circuit negative lookups when parent dir is fully cached

When the parent directory has a valid and complete cached enumeration we
can assume that negative dentries are not present in the directory, thus
we can return without issuing a request.

This reduces traffic for common ENOENT when the directory entries are
cached.

Signed-off-by: Henrique Carvalho <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: hac-v

fs/smb/client/dir.c

@@ -683,6 +683,7 @@ cifs_lookup(struct inode *parent_dir_inode, struct dentry *direntry,
 	const char *full_path;
 	void *page;
 	int retry_count = 0;
+	struct cached_fid *cfid = NULL;
 
 	xid = get_xid();
 
@@ -722,6 +723,28 @@ cifs_lookup(struct inode *parent_dir_inode, struct dentry *direntry,
 		cifs_dbg(FYI, "non-NULL inode in lookup\n");
 	} else {
 		cifs_dbg(FYI, "NULL inode in lookup\n");
+
+		/*
+		 * We can only rely on negative dentries having the same
+		 * spelling as the cached dirent if case insensitivity is
+		 * forced on mount.
+		 *
+		 * XXX: if servers correctly announce Case Sensitivity Search
+		 * on GetInfo of FileFSAttributeInformation, then we can take
+		 * correct action even if case insensitive is not forced on
+		 * mount.
+		 */
+		if (pTcon->nocase && !open_cached_dir_by_dentry(pTcon, direntry->d_parent, &cfid)) {
+			/*
+			 * dentry is negative and parent is fully cached:
+			 * we can assume file does not exist
+			 */
+			if (cfid->dirents.is_valid) {
+				close_cached_dir(cfid);
+				goto out;
+			}
+			close_cached_dir(cfid);
+		}
 	}
 	cifs_dbg(FYI, "Full path: %s inode = 0x%p\n",
 		 full_path, d_inode(direntry));
@@ -755,6 +778,8 @@ cifs_lookup(struct inode *parent_dir_inode, struct dentry *direntry,
 		}
 		newInode = ERR_PTR(rc);
 	}
+
+out:
 	free_dentry_path(page);
 	cifs_put_tlink(tlink);
 	free_xid(xid);
@@ -765,7 +790,8 @@ static int
 cifs_d_revalidate(struct inode *dir, const struct qstr *name,
 		  struct dentry *direntry, unsigned int flags)
 {
-	struct inode *inode;
+	struct inode *inode = NULL;
+	struct cached_fid *cfid;
 	int rc;
 
 	if (flags & LOOKUP_RCU)
@@ -812,6 +838,21 @@ cifs_d_revalidate(struct inode *dir, const struct qstr *name,
 
 			return 1;
 		}
+	} else {
+		struct cifs_sb_info *cifs_sb = CIFS_SB(dir->i_sb);
+		struct cifs_tcon *tcon = cifs_sb_master_tcon(cifs_sb);
+
+		if (!open_cached_dir_by_dentry(tcon, direntry->d_parent, &cfid)) {
+			/*
+			 * dentry is negative and parent is fully cached:
+			 * we can assume file does not exist
+			 */
+			if (cfid->dirents.is_valid) {
+				close_cached_dir(cfid);
+				return 1;
+			}
+			close_cached_dir(cfid);
+		}
 	}
 
 	/*