On Thu 10-09-09 16:34:55, Aneesh Kumar K.V wrote: > On Thu, Sep 10, 2009 at 12:52:16PM +0200, Jan Kara wrote: > > On Thu 10-09-09 14:45:51, Aneesh Kumar K.V wrote: > > > On Thu, Sep 10, 2009 at 02:34:49PM +0530, Aneesh Kumar K.V wrote: > > > > On Thu, Sep 10, 2009 at 10:50:56AM +0200, Jan Kara wrote: > > > > > Hi, > > > > > > > > > > On Thu 10-09-09 12:16:05, Aneesh Kumar K.V wrote: > > > > > > On Tue, Sep 08, 2009 at 03:26:01PM +0200, Jan Kara wrote: > > > > > > > When looking at how ext3/4 handles fsync, I've realized I don't > > > > > > > understand how writing out inode on fsync can work. The problem is that > > > > > > > ext3/4 mostly calls ext?_mark_inode_dirty() which actually does *not* dirty > > > > > > > the inode. It just copies the in-memory inode content to disk buffer. > > > > > > > So in particular the inode looks clean to VFS and our check in > > > > > > > ext?_sync_file() shouldn't trigger. > > > > > > > The only obvious case when we call mark_inode_dirty() is from write_end > > > > > > > functions when we update i_size but that's clearly not enough. Now I did > > > > > > > some research why things seem to be actually working. The trick is that > > > > > > > when allocating block, we call vfs_dq_alloc_block() which calls > > > > > > > mark_inode_dirty(). But that's all what's keeping our fsync / writeout > > > > > > > logic from breaking! > > > > > > > > > > > > ext4_handle_dirty_metadata should do mark_inode_dirty right ? > > > > > > __ext4_handle_dirty_metadata -> mark_buffer_dirty ->__set_page_dirty > > > > > > -> __mark_inode_dirty -> list_move(&inode->i_list, &sb->s_dirty); > > > > > ext4_handle_dirty_metadata() marks the buffer dirty only when we do not > > > > > have a journal (BTW, the inode that gets dirtied in the nojournal case > > > > > is the block-device one, not the one whose metadata we mark as dirty, so > > > > > it won't work there either - but Google guys are working on this I think). > > > > > With a journal the function just calls jbd2_journal_dirty_metadata which > > > > > does nothing with the inode. > > > > > > > > When we don't have a journal handle we do that as a part of journal commit > > > > right ? __jbd2_journal_temp_unlink_buffer -> mark_buffer_dirty > > > > > > > > I guess fsync only requires the meta data update to be in journal ? > > > > > > > > > > Adding the file inode to the sb->s_dirty is done through block_write_end ? > > > Why do you mention above that it is not "clearly not enough" ? > > Where? I don't see block_write_end() marking the inode dirty anywhere... > > It calls __block_commit_write() and that dirties only buffers, not the > > inode. > mark_buffer_dirty -> __set_page_dirty -> __mark_inode_dirty OK, but that sets only I_DIRTY_PAGES not I_DIRTY_DATA or I_DIRTY. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
