union-mount: Implement union-aware truncate()
Original-author: Valerie Aurora <vaurora@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com> (Further development)
diff --git a/fs/open.c b/fs/open.c
index fbe9f7c..3397dc8 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -64,7 +64,8 @@
static long do_sys_truncate(const char __user *pathname, loff_t length)
{
- struct path path;
+ struct path parent, path;
+ struct vfsmount *mnt;
struct inode *inode;
int error;
@@ -72,7 +73,7 @@
if (length < 0) /* sorry, but loff_t says... */
goto out;
- error = user_path(pathname, &path);
+ error = user_path_and_parent(AT_FDCWD, pathname, 0, &parent, &path);
if (error)
goto out;
inode = path.dentry->d_inode;
@@ -86,18 +87,50 @@
if (!S_ISREG(inode->i_mode))
goto dput_and_out;
- error = mnt_want_write(path.mnt);
+ /* If we're looking at the lower layer of a union mount, then we need
+ * to create the file on the upperfs and truncate that.
+ */
+ if (IS_MNT_LOWER(path.mnt) && parent.mnt)
+ mnt = parent.mnt;
+ else
+ mnt = path.mnt;
+
+ error = mnt_want_write(mnt);
if (error)
goto dput_and_out;
- error = inode_permission(inode, MAY_WRITE);
- if (error)
- goto mnt_drop_write_and_out;
+ if (unlikely(IS_MNT_UNION(mnt))) {
+ /* We have to be able to write to the upperfs. */
+ error = -EROFS;
+ if (mnt->mnt_sb->s_flags & MS_RDONLY)
+ goto mnt_drop_write_and_out;
+
+ /* But the lowerfs inode must offer write permission - if the
+ * lowerfs was mounted writably. */
+ error = __inode_permission(inode, MAY_WRITE);
+ if (error)
+ goto mnt_drop_write_and_out;
+ } else {
+ error = inode_permission(inode, MAY_WRITE);
+ if (error)
+ goto mnt_drop_write_and_out;
+ }
error = -EPERM;
if (IS_APPEND(inode))
goto mnt_drop_write_and_out;
+ if (IS_MNT_LOWER(path.mnt)) {
+ mutex_lock(&parent.dentry->d_inode->i_mutex);
+ error = union_copyup(&parent, &path, false, length);
+ mutex_unlock(&parent.dentry->d_inode->i_mutex);
+ if (error)
+ goto mnt_drop_write_and_out;
+ mntget(path.mnt);
+ }
+
+ /* path may have changed after copyup */
+ inode = path.dentry->d_inode;
error = get_write_access(inode);
if (error)
goto mnt_drop_write_and_out;
@@ -119,9 +152,10 @@
put_write_and_out:
put_write_access(inode);
mnt_drop_write_and_out:
- mnt_drop_write(path.mnt);
+ mnt_drop_write(mnt);
dput_and_out:
path_put(&path);
+ path_put(&parent);
out:
return error;
}
