int ntfs_readpage (struct file * file, struct page * page);
For non-resident attributes, ntfs_readpage fills the page of the open file file by calling the ntfs version of the generic block_read_full_page function, ntfs_read_block, which in turn creates and reads in the buffers associated with the page asynchronously.
For resident attributes, OTOH, ntfs_readpage fills page by copying the data from the mft record (which at this stage is most likely in memory) and fills the remainder with zeroes. Thus, in this case, I/O is synchronous, as even if the mft record is not cached at this point in time, we need to wait for it to be read in before we can do the copy.
Return 0 on success and -errno on error.
Do not make this function static! It is used by mft.c!