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, 36 insertions, 39 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index af49b3937e15..3d4e6e7dac1d 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -530,7 +530,8 @@ int cifs_open(struct inode *inode, struct file *file)
 	struct cifs_tcon *tcon;
 	struct tcon_link *tlink;
 	struct cifsFileInfo *cfile = NULL;
-	const char *full_path = NULL;
+	void *page;
+	const char *full_path;
 	bool posix_open_ok = false;
 	struct cifs_fid fid;
 	struct cifs_pending_open open;
@@ -546,9 +547,10 @@ int cifs_open(struct inode *inode, struct file *file)
 	tcon = tlink_tcon(tlink);
 	server = tcon->ses->server;
 
-	full_path = build_path_from_dentry(file_dentry(file));
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	page = alloc_dentry_path();
+	full_path = build_path_from_dentry(file_dentry(file), page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
 		goto out;
 	}
 
@@ -640,7 +642,7 @@ int cifs_open(struct inode *inode, struct file *file)
 	}
 
 out:
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 	cifs_put_tlink(tlink);
 	return rc;
@@ -689,7 +691,8 @@ cifs_reopen_file(struct cifsFileInfo *cfile, bool can_flush)
 	struct TCP_Server_Info *server;
 	struct cifsInodeInfo *cinode;
 	struct inode *inode;
-	const char *full_path = NULL;
+	void *page;
+	const char *full_path;
 	int desired_access;
 	int disposition = FILE_OPEN;
 	int create_options = CREATE_NOT_DIR;
@@ -699,9 +702,8 @@ cifs_reopen_file(struct cifsFileInfo *cfile, bool can_flush)
 	mutex_lock(&cfile->fh_mutex);
 	if (!cfile->invalidHandle) {
 		mutex_unlock(&cfile->fh_mutex);
-		rc = 0;
 		free_xid(xid);
-		return rc;
+		return 0;
 	}
 
 	inode = d_inode(cfile->dentry);
@@ -715,12 +717,13 @@ cifs_reopen_file(struct cifsFileInfo *cfile, bool can_flush)
 	 * called and if the server was down that means we end up here, and we
 	 * can never tell if the caller already has the rename_sem.
 	 */
-	full_path = build_path_from_dentry(cfile->dentry);
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	page = alloc_dentry_path();
+	full_path = build_path_from_dentry(cfile->dentry, page);
+	if (IS_ERR(full_path)) {
 		mutex_unlock(&cfile->fh_mutex);
+		free_dentry_path(page);
 		free_xid(xid);
-		return rc;
+		return PTR_ERR(full_path);
 	}
 
 	cifs_dbg(FYI, "inode = 0x%p file flags 0x%x for %s\n",
@@ -838,7 +841,7 @@ reopen_success:
 		cifs_relock_file(cfile);
 
 reopen_error_exit:
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 	return rc;
 }
@@ -2069,34 +2072,31 @@ cifs_get_writable_path(struct cifs_tcon *tcon, const char *name,
 		       int flags,
 		       struct cifsFileInfo **ret_file)
 {
-	struct list_head *tmp;
 	struct cifsFileInfo *cfile;
-	struct cifsInodeInfo *cinode;
-	const char *full_path;
+	void *page = alloc_dentry_path();
 
 	*ret_file = NULL;
 
 	spin_lock(&tcon->open_file_lock);
-	list_for_each(tmp, &tcon->openFileList) {
-		cfile = list_entry(tmp, struct cifsFileInfo,
-			     tlist);
-		full_path = build_path_from_dentry(cfile->dentry);
-		if (full_path == NULL) {
+	list_for_each_entry(cfile, &tcon->openFileList, tlist) {
+		struct cifsInodeInfo *cinode;
+		const char *full_path = build_path_from_dentry(cfile->dentry, page);
+		if (IS_ERR(full_path)) {
 			spin_unlock(&tcon->open_file_lock);
-			return -ENOMEM;
+			free_dentry_path(page);
+			return PTR_ERR(full_path);
 		}
-		if (strcmp(full_path, name)) {
-			kfree(full_path);
+		if (strcmp(full_path, name))
 			continue;
-		}
 
-		kfree(full_path);
 		cinode = CIFS_I(d_inode(cfile->dentry));
 		spin_unlock(&tcon->open_file_lock);
+		free_dentry_path(page);
 		return cifs_get_writable_file(cinode, flags, ret_file);
 	}
 
 	spin_unlock(&tcon->open_file_lock);
+	free_dentry_path(page);
 	return -ENOENT;
 }
 
@@ -2104,35 +2104,32 @@ int
 cifs_get_readable_path(struct cifs_tcon *tcon, const char *name,
 		       struct cifsFileInfo **ret_file)
 {
-	struct list_head *tmp;
 	struct cifsFileInfo *cfile;
-	struct cifsInodeInfo *cinode;
-	const char *full_path;
+	void *page = alloc_dentry_path();
 
 	*ret_file = NULL;
 
 	spin_lock(&tcon->open_file_lock);
-	list_for_each(tmp, &tcon->openFileList) {
-		cfile = list_entry(tmp, struct cifsFileInfo,
-			     tlist);
-		full_path = build_path_from_dentry(cfile->dentry);
-		if (full_path == NULL) {
+	list_for_each_entry(cfile, &tcon->openFileList, tlist) {
+		struct cifsInodeInfo *cinode;
+		const char *full_path = build_path_from_dentry(cfile->dentry, page);
+		if (IS_ERR(full_path)) {
 			spin_unlock(&tcon->open_file_lock);
-			return -ENOMEM;
+			free_dentry_path(page);
+			return PTR_ERR(full_path);
 		}
-		if (strcmp(full_path, name)) {
-			kfree(full_path);
+		if (strcmp(full_path, name))
 			continue;
-		}
 
-		kfree(full_path);
 		cinode = CIFS_I(d_inode(cfile->dentry));
 		spin_unlock(&tcon->open_file_lock);
+		free_dentry_path(page);
 		*ret_file = find_readable_file(cinode, 0);
 		return *ret_file ? 0 : -ENOENT;
 	}
 
 	spin_unlock(&tcon->open_file_lock);
+	free_dentry_path(page);
 	return -ENOENT;
 }