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, 28 insertions, 18 deletions

diff --git a/fs/cifs/link.c b/fs/cifs/link.c
index 18e0e31a6d39..616e1bc0cc0a 100644
--- a/fs/cifs/link.c
+++ b/fs/cifs/link.c
@@ -510,8 +510,8 @@ cifs_hardlink(struct dentry *old_file, struct inode *inode,
 {
 	int rc = -EACCES;
 	unsigned int xid;
-	const char *from_name = NULL;
-	const char *to_name = NULL;
+	const char *from_name, *to_name;
+	void *page1, *page2;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
 	struct tcon_link *tlink;
 	struct cifs_tcon *tcon;
@@ -524,11 +524,17 @@ cifs_hardlink(struct dentry *old_file, struct inode *inode,
 	tcon = tlink_tcon(tlink);
 
 	xid = get_xid();
+	page1 = alloc_dentry_path();
+	page2 = alloc_dentry_path();
 
-	from_name = build_path_from_dentry(old_file);
-	to_name = build_path_from_dentry(direntry);
-	if ((from_name == NULL) || (to_name == NULL)) {
-		rc = -ENOMEM;
+	from_name = build_path_from_dentry(old_file, page1);
+	if (IS_ERR(from_name)) {
+		rc = PTR_ERR(from_name);
+		goto cifs_hl_exit;
+	}
+	to_name = build_path_from_dentry(direntry, page2);
+	if (IS_ERR(to_name)) {
+		rc = PTR_ERR(to_name);
 		goto cifs_hl_exit;
 	}
 
@@ -587,8 +593,8 @@ cifs_hardlink(struct dentry *old_file, struct inode *inode,
 	}
 
 cifs_hl_exit:
-	kfree(from_name);
-	kfree(to_name);
+	free_dentry_path(page1);
+	free_dentry_path(page2);
 	free_xid(xid);
 	cifs_put_tlink(tlink);
 	return rc;
@@ -600,7 +606,8 @@ cifs_get_link(struct dentry *direntry, struct inode *inode,
 {
 	int rc = -ENOMEM;
 	unsigned int xid;
-	const char *full_path = NULL;
+	const char *full_path;
+	void *page;
 	char *target_path = NULL;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
 	struct tcon_link *tlink = NULL;
@@ -620,11 +627,13 @@ cifs_get_link(struct dentry *direntry, struct inode *inode,
 	tcon = tlink_tcon(tlink);
 	server = tcon->ses->server;
 
-	full_path = build_path_from_dentry(direntry);
-	if (!full_path) {
+	page = alloc_dentry_path();
+	full_path = build_path_from_dentry(direntry, page);
+	if (IS_ERR(full_path)) {
 		free_xid(xid);
 		cifs_put_tlink(tlink);
-		return ERR_PTR(-ENOMEM);
+		free_dentry_path(page);
+		return ERR_CAST(full_path);
 	}
 
 	cifs_dbg(FYI, "Full path: %s inode = 0x%p\n", full_path, inode);
@@ -649,7 +658,7 @@ cifs_get_link(struct dentry *direntry, struct inode *inode,
 						&target_path, reparse_point);
 	}
 
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 	cifs_put_tlink(tlink);
 	if (rc != 0) {
@@ -669,7 +678,8 @@ cifs_symlink(struct user_namespace *mnt_userns, struct inode *inode,
 	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
 	struct tcon_link *tlink;
 	struct cifs_tcon *pTcon;
-	const char *full_path = NULL;
+	const char *full_path;
+	void *page = alloc_dentry_path();
 	struct inode *newinode = NULL;
 
 	xid = get_xid();
@@ -681,9 +691,9 @@ cifs_symlink(struct user_namespace *mnt_userns, struct inode *inode,
 	}
 	pTcon = tlink_tcon(tlink);
 
-	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 symlink_exit;
 	}
 
@@ -719,7 +729,7 @@ cifs_symlink(struct user_namespace *mnt_userns, struct inode *inode,
 		}
 	}
 symlink_exit:
-	kfree(full_path);
+	free_dentry_path(page);
 	cifs_put_tlink(tlink);
 	free_xid(xid);
 	return rc;