int ntfs_setattr (struct dentry * dentry, struct iattr * attr);
We have to trap VFS attempts to truncate the file described by dentry as soon as possible, because we do not implement changes in i_size yet. So we abort all i_size changes here.
We also abort all changes of user, group, and mode as we do not implement the NTFS ACLs yet.
Called with ->i_sem held. For the ATTR_SIZE (i.e. ->truncate) case, also called with ->i_alloc_sem held for writing.
Basically this is a copy of generic notify_change and inode_setattr functionality, except we intercept and abort changes in i_size.