linux-kernel - Re: debugfs_remove_recursive() while a file is in use by userspace

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Message-ID: <20151228205833.GA20955@kroah.com>
Date:	Mon, 28 Dec 2015 12:58:33 -0800
From:	Greg Kroah-Hartman <greg@...ah.com>
To:	Rajat Jain <rajatxjain@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-newbie@...r.kernel.org
Subject: Re: debugfs_remove_recursive() while a file is in use by userspace

On Mon, Dec 28, 2015 at 12:51:32PM -0800, Rajat Jain wrote:
> Thanks Greg and Al for the quick turnaround.
> 
> Essentially I have a device that supports something called "contexts"
> that can be "created" and "destroyed" during the life of the device. I
> want to expose some debug files for the context when it is created,
> and destroy the files when the context is destroyed. However, I'm not
> sure how do I ensure that the user is not in the middle of reading /
> writing / mmaping to those files. Also how do I know that user is
> still not holding a reference to the file structure.

You don't.

> It seems like debugfs is currently not a good choice for this? Would
> you recommend me to any other fs or subsystem that I should use for
> this?

What exactly do you need to export to userspace and for what purpose?
For debugging-only stuff, sure, use debugfs, but don't rely on it for
any "real" tools, only your own debugging.

> Would hanging those files under the sysfs node for the device sound
> any better (by representing each "context" using an embedded kobject)?

That would ensure that things work properly.  But you don't need a whole
kobject, just use a named group and a subdir will be created properly
for you.

good luck,

greg k-h
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