On Fri, Oct 23, 2020 at 06:44:23PM +0300, Konstantin Komarov wrote:
> +
> +/*ntfs_readpage*/
> +/*ntfs_readpages*/
> +/*ntfs_writepage*/
> +/*ntfs_writepages*/
> +/*ntfs_block_truncate_page*/
What are these for?
> +int ntfs_readpage(struct file *file, struct page *page)
> +{
> + int err;
> + struct address_space *mapping = page->mapping;
> + struct inode *inode = mapping->host;
> + struct ntfs_inode *ni = ntfs_i(inode);
> + u64 vbo = (u64)page->index << PAGE_SHIFT;
> + u64 valid;
> + struct ATTRIB *attr;
> + const char *data;
> + u32 data_size;
> +
[...]
> +
> + if (is_compressed(ni)) {
> + if (PageUptodate(page)) {
> + unlock_page(page);
> + return 0;
> + }
You can skip this -- the readpage op won't be called for pages which
are Uptodate.
> + /* normal + sparse files */
> + err = mpage_readpage(page, ntfs_get_block);
> + if (err)
> + goto out;
It would be nice to use iomap instead of mpage, but that's a big ask.
> + valid = ni->i_valid;
> + if (vbo < valid && valid < vbo + PAGE_SIZE) {
> + if (PageLocked(page))
> + wait_on_page_bit(page, PG_locked);
> + if (PageError(page)) {
> + ntfs_inode_warn(inode, "file garbage at 0x%llx", valid);
> + goto out;
> + }
> + zero_user_segment(page, valid & (PAGE_SIZE - 1), PAGE_SIZE);
Nono, you can't zero data after the page has been unlocked. You can
handle this case in ntfs_get_block(). If the block is entirely beyond
i_size, returning a hole will cause mpage_readpage() to zero it. If it
straddles i_size, you can either ensure that the on-media block contains
zeroes after the EOF, or if you can't depend on that, you can read it
in synchronously in your get_block() and then zero the tail and set the
buffer Uptodate. Not the most appetising solution, but what you have here
is racy with the user writing to it after reading.
