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 ? -aneesh -- 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
