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, 18 insertions, 12 deletions

diff --git a/fs/cifs/xattr.c b/fs/cifs/xattr.c
index 0195a9be3d28..e351b945135b 100644
--- a/fs/cifs/xattr.c
+++ b/fs/cifs/xattr.c
@@ -113,6 +113,7 @@ static int cifs_xattr_set(const struct xattr_handler *handler,
 	struct tcon_link *tlink;
 	struct cifs_tcon *pTcon;
 	const char *full_path;
+	void *page;
 
 	tlink = cifs_sb_tlink(cifs_sb);
 	if (IS_ERR(tlink))
@@ -120,10 +121,11 @@ static int cifs_xattr_set(const struct xattr_handler *handler,
 	pTcon = tlink_tcon(tlink);
 
 	xid = get_xid();
+	page = alloc_dentry_path();
 
-	full_path = build_path_from_dentry(dentry);
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	full_path = build_path_from_dentry(dentry, page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
 		goto out;
 	}
 	/* return dos attributes as pseudo xattr */
@@ -235,7 +237,7 @@ static int cifs_xattr_set(const struct xattr_handler *handler,
 	}
 
 out:
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 	cifs_put_tlink(tlink);
 	return rc;
@@ -298,6 +300,7 @@ static int cifs_xattr_get(const struct xattr_handler *handler,
 	struct tcon_link *tlink;
 	struct cifs_tcon *pTcon;
 	const char *full_path;
+	void *page;
 
 	tlink = cifs_sb_tlink(cifs_sb);
 	if (IS_ERR(tlink))
@@ -305,10 +308,11 @@ static int cifs_xattr_get(const struct xattr_handler *handler,
 	pTcon = tlink_tcon(tlink);
 
 	xid = get_xid();
+	page = alloc_dentry_path();
 
-	full_path = build_path_from_dentry(dentry);
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	full_path = build_path_from_dentry(dentry, page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
 		goto out;
 	}
 
@@ -401,7 +405,7 @@ static int cifs_xattr_get(const struct xattr_handler *handler,
 		rc = -EOPNOTSUPP;
 
 out:
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 	cifs_put_tlink(tlink);
 	return rc;
@@ -415,6 +419,7 @@ ssize_t cifs_listxattr(struct dentry *direntry, char *data, size_t buf_size)
 	struct tcon_link *tlink;
 	struct cifs_tcon *pTcon;
 	const char *full_path;
+	void *page;
 
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_XATTR)
 		return -EOPNOTSUPP;
@@ -425,10 +430,11 @@ ssize_t cifs_listxattr(struct dentry *direntry, char *data, size_t buf_size)
 	pTcon = tlink_tcon(tlink);
 
 	xid = get_xid();
+	page = alloc_dentry_path();
 
-	full_path = build_path_from_dentry(direntry);
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	full_path = build_path_from_dentry(direntry, page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
 		goto list_ea_exit;
 	}
 	/* return dos attributes as pseudo xattr */
@@ -442,7 +448,7 @@ ssize_t cifs_listxattr(struct dentry *direntry, char *data, size_t buf_size)
 		rc = pTcon->ses->server->ops->query_all_EAs(xid, pTcon,
 				full_path, NULL, data, buf_size, cifs_sb);
 list_ea_exit:
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 	cifs_put_tlink(tlink);
 	return rc;