linux-kernel - Re: [PATCH] fs: add the FIGETFROZEN ioctl call

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Message-ID: <20160415005052.6734gfnt7kjpwxyc@mguzik>
Date:	Fri, 15 Apr 2016 02:50:54 +0200
From:	Mateusz Guzik <mguzik@...hat.com>
To:	Florian Margaine <florian@...gaine.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: add the FIGETFROZEN ioctl call

On Thu, Apr 14, 2016 at 09:57:07AM +0200, Florian Margaine wrote:
> This lets userland get the filesystem freezing status, aka whether the
> filesystem is frozen or not. This is so that an application can know if
> it should freeze the filesystem or if it isn't necessary when taking a
> snapshot.

The feature may be useful in general, I don't know.

However, I'm confused why programs would depend on it. If you froze
a particular subsystem, you don't have to check. If you did not, what
prevents whoever originaly froze it from unfreezing as you access it?

As such, maybe the feature you are looking for would count how many
times the fs is frozen.

-- 
Mateusz Guzik