On Wed, 19 Sep 2007 16:43:08 +0900 KAMEZAWA Hiroyuki <[EMAIL PROTECTED]> wrote:
> A clarification of page <-> fs interface (page cache). > > At first, each FS has to access to struct page->mapping directly. > But it's not just pointer. (we use special 1bit enconding for anon.) > > Although there is historical consensus that page->mapping points to its > inode's > address space, I think adding some neat helper functon is not bad. > > This patch adds page-cache.h which containes page<->address_space<->inode > function which is required (used) by subsystems. > > Following functions are added > > * page_mapping_cache() ... returns address space if a page is page cache > * page_mapping_anon() ... returns anon_vma if a page is anonymous page. > * page_is_pagecache() ... returns true if a page is page-cache. > * page_inode() ... returns inode which a page-cache belongs to. > * is_page_consistent() ... returns true if a page is still valid page cache > > Followings are moved > * page_mapping() ... returns swapper_space or address_space a page is > on. > (from mm.h) > * page_index() ... returns position of a page in its inode > (from mm.h) > * remove_mapping() ... a safe routine to remove page->mapping from page. > (from swap.h) I have two other functions that might want integration with this scheme: page_file_mapping() ... returns backing address space page_file_index() ... returns the index therein They are identical to page_mapping_cache() and page_index() for page cache pages, but they also work on swap cache pages. That is, for swapcache pages they return: page_file_mapping: page_swap_info(page)->swap_file->f_mapping page_file_index: swp_offset((swp_offset_t)page_private(page)) When a filesystem uses these functions instead of page->mapping and page->index, it allows passing swap cache pages into the regular filesystem read/write paths. This is useful for things like swap over NFS, where swap is backed by a swapfile on a 'regular' filesystem. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
