pagecache_isize_extended(9) update pagecache after extension of i_size


void pagecache_isize_extended(struct inode * inode, loff_t from, loff_t to);



inode for which i_size was extended


original inode size


new inode size


Handle extension of inode size either caused by extending truncate or by write starting after current i_size. We mark the page straddling current i_size RO so that page_mkwrite is called on the nearest write access to the page. This way filesystem can be sure that page_mkwrite is called on the page before user writes to the page via mmap after the i_size has been changed.

The function must be called after i_size is updated so that page fault coming after we unlock the page will already see the new i_size. The function must be called while we still hold i_mutex - this not only makes sure i_size is stable but also that userspace cannot observe new i_size value before we are prepared to store mmap writes at new inode size.