cifs: allocate buffer in the caller of build_path_from_dentry()

build_path_from_dentry() open-codes dentry_path_raw().  The reason
we can't use dentry_path_raw() in there (and postprocess the
result as needed) is that the callers of build_path_from_dentry()
expect that the object to be freed on cleanup and the string to
be used are at the same address.  That's painful, since the path
is naturally built end-to-beginning - we start at the leaf and
go through the ancestors, accumulating the pathname.

Life would be easier if we left the buffer allocation to callers.
It wouldn't be exact-sized buffer, but none of the callers keep
the result for long - it's always freed before the caller returns.
So there's no need to do exact-sized allocation; better use
__getname()/__putname(), same as we do for pathname arguments
of syscalls.  What's more, there's no need to do allocation under
spinlocks, so GFP_ATOMIC is not needed.

Next patch will replace the open-coded dentry_path_raw() (in
build_path_from_dentry_optional_prefix()) with calling the real
thing.  This patch only introduces wrappers for allocating/freeing
the buffers and switches to new calling conventions:
	build_path_from_dentry(dentry, buf)
expects buf to be address of a page-sized object or NULL,
return value is a pathname built inside that buffer on success,
ERR_PTR(-ENOMEM) if buf is NULL and ERR_PTR(-ENAMETOOLONG) if
the pathname won't fit into page.  Note that we don't need to
check for failure when allocating the buffer in the caller -
build_path_from_dentry() will do the right thing.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/fs/cifs/readdir.c b/fs/cifs/readdir.c
index 67c3177a1fda..7531e8905881 100644
--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -942,13 +942,14 @@ int cifs_readdir(struct file *file, struct dir_context *ctx)
 	char *tmp_buf = NULL;
 	char *end_of_smb;
 	unsigned int max_len;
-	const char *full_path = NULL;
+	const char *full_path;
+	void *page = alloc_dentry_path();
 
 	xid = get_xid();
 
-	full_path = build_path_from_dentry(file_dentry(file));
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	full_path = build_path_from_dentry(file_dentry(file), page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
 		goto rddir2_exit;
 	}
 
@@ -1043,7 +1044,7 @@ int cifs_readdir(struct file *file, struct dir_context *ctx)
 	kfree(tmp_buf);
 
 rddir2_exit:
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 	return rc;
 }