s3: Fix trans2 path to use case-insensitive stat optimization

Often times before creating a file, a client will first query to see
if it already exists.  Since some systems have a case-insensitive stat
that is called from unix_convert, we can definitively return
STATUS_NO_SUCH_FILE to the client without scanning the whole
directory.

This code path is taken from trans2querypathinfo, but trans2findfirst
still does a full directory scan even though the get_real_filename
(the case-insensitive stat vfs call) can prevent this.

This patch adds the get_real_filename call to the trans2find* path,
and also changes the vfs_default behavior for
SMB_VFS_GET_REAL_FILENAME.  Previously, in the absence of a
get_real_filename implementation, we would fallback to the full
directory scan.  The default behavior now returns -1 and sets errno to
EOPNOTSUPP.  This allows SMB_VFS_GET_REALFILENAME to be called from
trans2* and unix_convert.
(cherry picked from commit 92558a875ebf842e652614a5519ae101dd62ffd1)

2 files changed, 51 insertions, 6 deletions

diff --git a/source3/smbd/dir.c b/source3/smbd/dir.c
index b4a8f942c24..e7902871d38 100644
--- a/source3/smbd/dir.c
+++ b/source3/smbd/dir.c
@@ -576,6 +576,9 @@ const char *dptr_ReadDirName(TALLOC_CTX *ctx,
 {
 	char *name = NULL;
 	char *pathreal = NULL;
+	char *found_name = NULL;
+	int ret;
+
 	SET_STAT_INVALID(*pst);
 
 	if (dptr->has_wild || dptr->did_stat) {
@@ -640,6 +643,20 @@ const char *dptr_ReadDirName(TALLOC_CTX *ctx,
 		goto clean;
 	}
 
+	/*
+	 * Try case-insensitive stat if the fs has the ability. This avoids
+	 * scanning the whole directory.
+	 */
+	ret = SMB_VFS_GET_REAL_FILENAME(dptr->conn, dptr->path, dptr->wcard,
+					ctx, &found_name);
+	if (ret == 0) {
+		name = found_name;
+		goto clean;
+	} else if (errno == ENOENT) {
+		/* The case-insensitive lookup was authoritative. */
+		goto clean;
+	}
+
 	TALLOC_FREE(pathreal);
 
 	return dptr_normal_ReadDirName(dptr, poffset, pst);
diff --git a/source3/smbd/filename.c b/source3/smbd/filename.c
index 80722a7cd08..774ab27a74b 100644
--- a/source3/smbd/filename.c
+++ b/source3/smbd/filename.c
@@ -447,9 +447,9 @@ NTSTATUS unix_convert(TALLOC_CTX *ctx,
 			 */
 
 			if (name_has_wildcard ||
-			    (SMB_VFS_GET_REAL_FILENAME(
-				     conn, dirpath, start,
-				     talloc_tos(), &found_name) == -1)) {
+			    (get_real_filename(conn, dirpath, start,
+					       talloc_tos(),
+					       &found_name) == -1)) {
 				char *unmangled;
 
 				if (end) {
@@ -789,9 +789,9 @@ static bool fname_equal(const char *name1, const char *name2,
  If the name looks like a mangled name then try via the mangling functions
 ****************************************************************************/
 
-int get_real_filename(connection_struct *conn, const char *path,
-		      const char *name, TALLOC_CTX *mem_ctx,
-		      char **found_name)
+static int get_real_filename_full_scan(connection_struct *conn,
+				       const char *path, const char *name,
+				       TALLOC_CTX *mem_ctx, char **found_name)
 {
 	struct smb_Dir *cur_dir;
 	const char *dname;
@@ -887,6 +887,34 @@ int get_real_filename(connection_struct *conn, const char *path,
 	return -1;
 }
 
+/****************************************************************************
+ Wrapper around the vfs get_real_filename and the full directory scan
+ fallback.
+****************************************************************************/
+
+int get_real_filename(connection_struct *conn, const char *path,
+		      const char *name, TALLOC_CTX *mem_ctx,
+		      char **found_name)
+{
+	int ret;
+
+	/* Try the vfs first to take advantage of case-insensitive stat. */
+	ret = SMB_VFS_GET_REAL_FILENAME(conn, path, name, mem_ctx, found_name);
+
+	/*
+	 * If the case-insensitive stat was successful, or returned an error
+	 * other than EOPNOTSUPP then there is no need to fall back on the
+	 * full directory scan.
+	 */
+	if (ret == 0 || (ret == -1 && errno != EOPNOTSUPP)) {
+		return ret;
+	}
+
+	ret = get_real_filename_full_scan(conn, path, name, mem_ctx,
+					  found_name);
+	return ret;
+}
+
 static NTSTATUS build_stream_path(TALLOC_CTX *mem_ctx,
 				  connection_struct *conn,
 				  const char *orig_path,