Hi, 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! There are even some cases when the logic actually is broken (I've tested it and it really does not work) - for example when you create an empty file, the inode won't get written when you fsync it. So what we should IMHO do is to convert all ext?_mark_inode_dirty() calls to simple mark_inode_dirty() (or even maybe introduce and use mark_inode_dirty_datasync() where appropriate). It will cost us some more CPU and stack space but if we optimize ext3_dirty_inode() for the case where handle is already started, it shouldn't be too bad. 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
