linux-kernel - Re: [RFC] simple_recursive

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Date:   Fri, 15 Nov 2019 21:18:20 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>, yu kuai <yukuai3@...wei.com>,
        rafael@...nel.org, oleg@...hat.com, mchehab+samsung@...nel.org,
        corbet@....net, tytso@....edu, jmorris@...ei.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        zhengbin13@...wei.com, yi.zhang@...wei.com,
        chenxiang66@...ilicon.com, xiexiuqi@...wei.com
Subject: Re: [RFC] simple_recursive_removal()

On Fri, Nov 15, 2019 at 07:41:38PM +0000, Al Viro wrote:
> On Fri, Nov 15, 2019 at 06:42:09PM +0000, Al Viro wrote:
> > Come to think of that, if we use IS_DEADDIR as "no more additions" marking,
> > that looks like a good candidate for all in-kernel rm -rf on ramfs-style
> > filesystems without cross-directory renames.  This bit in kill_it() above
> >  		if victim is regular
> >  			__debugfs_file_removed(victim)
> > would be an fs-specific callback passed by the caller, turning the whole
> > thing into this:
> 
> Umm...  A bit more than that, actually - the callback would be
> void remove_one(struct dentry *victim)
> {
> 	if (d_is_reg(victim))
> 		__debugfs_file_removed(victim);
> 	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
> }
> and the caller would do
> 	simple_pin_fs(&debug_fs_type, &debugfs_mount, &debugfs_mount_count);
> 	simple_recursive_removal(dentry, remove_one);
> 	simple_release_fs(&debugfs_mount, &debugfs_mount_count);

OK... debugfs and tracefs definitely convert to that; so do, AFAICS,
spufs and selinuxfs, and I wouldn't be surprised if it could be
used in a few more places...  securityfs, almost certainly qibfs,
gadgetfs looks like it could make use of that.  Maybe subrpc
as well, but I'll need to look in details.  configfs won't,
unfortunately...