linux-kernel - Re: [PATCH] loop: Disable fallocate() zero and discard if not supported

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Date: Mon, 10 Jun 2024 07:14:42 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Cyril Hrubis <chrubis@...e.cz>
Cc: Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...nel.dk>,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jan Kara <jack@...e.cz>
Subject: Re: [PATCH] loop: Disable fallocate() zero and discard if not
 supported

On Mon, Jun 10, 2024 at 04:13:23PM +0200, Cyril Hrubis wrote:
> Do we need noinline attribute for the function as well or unlikely() in
> the if condition?

unlikely sounds like the right thing here.

> > (and maybe one day we figure out a way for the file system to
> > advertise what fallocate modes it actually supports..)
> 
> One of my ideas was to try fallocate() with zero size in the
> loop_reconfigure_limits() to see if we get EOPNOTSUPP but for that to
> work we would have to make sure that we do not bail early on zero size
> in the vfs layer...

And the VFS layer doesn't know, it has to go all the way into the
file system..