Re: Filling holes in ext2

[Andrew Morton <akpm@zip.com.au>]

Adrian Cox wrote:
> 
> Andrew Morton wrote:
> 
> > It matters.  -ac kernels handle this by clearing out the blocks
> > on the error path in __block_prepare_write().  If you retest with
> > -ac kernels, you should just see zeroes.
> 
> That doesn't help. The problem occurs just the same on -ac kernels.

OK, that code is for IO errors and disk-full.

> In this case __block_prepare_write() is successful. What happens is that
> if __copy_from_user() fails, the block remains mapped but not up to
> date. Thus the next read access to the file fetches the garbage data off
> disk, and presents it to the user.

generic_file_write() will mark the page not up-to-date in this case.
I wonder what's actually going on?  Perhaps the fact that we've
instantiated a block in ext2 outside i_size?

If you change the error path in -ac's generic_file_write() thusly:

-	goto fail_write;
+	status = -EFAULT;
+	goto sync_failure;

does it fix it?

Can you send the code you're using to demonstrate this?

-