linux-kernel - Re: [RFC v4+ hot_track 13/19] debugfs: introduce one function

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Date:	Mon, 29 Oct 2012 15:54:21 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Zhi Yong Wu <zwu.kernel@...il.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linuxram@...ux.vnet.ibm.com, viro@...iv.linux.org.uk,
	david@...morbit.com, tytso@....edu, cmm@...ibm.com,
	wuzhy@...ux.vnet.ibm.com, wenqing.lz@...bao.com
Subject: Re: [RFC v4+ hot_track 13/19] debugfs: introduce one function

On Tue, Oct 30, 2012 at 06:45:19AM +0800, Zhi Yong Wu wrote:
> On Tue, Oct 30, 2012 at 6:34 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> > On Tue, Oct 30, 2012 at 06:25:50AM +0800, Zhi Yong Wu wrote:
> >> On Tue, Oct 30, 2012 at 2:11 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> >> > On Mon, Oct 29, 2012 at 12:30:55PM +0800, zwu.kernel@...il.com wrote:
> >> >> From: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
> >> >>
> >> >>   The debugfs function is used to get expected dentry.
> >> >
> >> > Huh?  Why do you need this?  Why haven't you added documentation for the
> >> It is used to determine if one sysfs directory has been created. OK, i
> >> will add some doc, thanks for your suggestion.
> >
> > You didn't answer the "why" part here.  How come you think you need
> ah, Let me say its scenario at first. If we do two mount ops as below:
> 1.) mount -o loop,hot_track image1 /data1
> 2.) mount -o loop,hot_track image2 /data2
> 
> The mount -o hot_track operation will automatically create one sysfs
> directory /sys/kernel/debug/hot_track. To prevent this dir being
> created again when 2.) is done, we need to know if it has existed at
> first. In my patch, i at first get its dentry by this new function,
> then determine if its d_inode field is NULL, if no, it means that this
> sysfs dir has existed.
> This is the reason that i want to add one new function.

Why not do like the rest of the kernel does and just have a:
	static dentry *hot_track_root;
and use that as your root debugfs directory dentry:

	if (!hot_track_root) {
		/* Create root directory */
		hot_track_root = debugfs_create(...);
	}

No need to look anything up :)

thanks,

greg k-h
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