Re: [PATCH] ext4: minor defrag code improvements

[Eric Whitney <enwlinux@gmail.com>]

* Theodore Ts'o <tytso@mit.edu>:
> On Wed, Jul 20, 2022 at 11:11:38AM -0400, Eric Whitney wrote:
> > > Is ETXTBUSY still reported by the kernel?  I couldn't find it in a search after
> > > reading this:  lwn.net/Articles/866493/
> > > I didn't consider that because an executable wasn't involved - interesting that
> > > it was used for some operations applied to swap files.
> 
> The LWN article is specifically about whether it's worth it to block
> writes to executable files.
> 
> However, if you look at some places where ETXTBSY is returned, such as
> in fs/open.c and fs/read_write.c, it's being returned when there is
> attempt to operate on a swap file using fallocate(2), write(2) or
> copy_file(2).  So I agree with Jan that it's better for the defrag
> code to be consistent those uses of ETXTBSY.
> 
> I'll also add that, "busy" does make some sense as a concept, since if
> you run "swapoff", you can now defrag the file, since it's no longer
> being used as a swap file --- hence, it's no longer busy.  So I don't
> have as visceral reaction to using EBUSY, but given the other ways
> defrag might return EBUSY where it *would* make sense to retry the
> defrag, I agree that changing the error return in the case of an
> attempted defrag of a swap file to ETXTBSY makes sense.
> 
> 						- Ted

Thanks for your review.  I'll modify the patch to return ETXTBSY and repost.

Eric