linux-ext4 - Re: [PATCH] ext4: minor defrag code improvements

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Message-ID: <Ytq4SDKXE0rqVUVD@debian-BULLSEYE-live-builder-AMD64>
Date:   Fri, 22 Jul 2022 10:46:32 -0400
From:   Eric Whitney <enwlinux@...il.com>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Eric Whitney <enwlinux@...il.com>, Jan Kara <jack@...e.cz>,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: minor defrag code improvements

* Theodore Ts'o <tytso@....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