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Date: Mon, 12 Feb 2024 17:47:40 -0500
From: "Theodore Ts'o" <tytso@mit.edu>
To: Kent Overstreet <kent.overstreet@linux.dev>
Cc: brauner@kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/7] filesystem visibililty ioctls
Message-ID: <20240212224740.GA394352@mit.edu>
References: <20240206201858.952303-1-kent.overstreet@linux.dev>
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On Wed, Feb 07, 2024 at 03:26:55PM -0500, Kent Overstreet wrote:
> You've still got the ext4 version, we're not taking that away. But I
> don't think other filesystems will want to deal with the hassle of
> changing UUIDs at runtime, since that's effectively used for API access
> via sysfs and debugfs.

Thanks. I misunderstood the log.  I didn't realize this was just about
not hoisting the ioctl to the VFS level, and dropping the generic uuid
set.

I'm not convinced that we should be using the UUID for kernel API
access, if for no other reason that not all file systems have UUID's.
Sure, modern file systems have UUID's, and individual file systems
might have to have specific features that don't play well with UUID's
changing while the file system is mounted.  But I'm hoping that we
don't add any new interfaces that rely on using the UUID for API
access at the VFS layer.  After all, ext2 (not just ext3 and ext4) has
supported changing the UUID while the file system has been mounted for
*decades*.

     	       	    	       	    	    - Ted