linux-kernel - Re: [RFC PATCH 1/4] fs: Add FS_XFLAG_COMPRESSED & FS_XFLAG_ENCRYPTED for FS_IOC

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Message-ID: <Z7UQHL5odYOBqAvo@dread.disaster.area>
Date: Wed, 19 Feb 2025 09:56:28 +1100
From: Dave Chinner <david@...morbit.com>
To: Pali Rohár <pali@...nel.org>
Cc: Amir Goldstein <amir73il@...il.com>, Eric Biggers <ebiggers@...nel.org>,
	"Darrick J. Wong" <djwong@...nel.org>,
	ronnie sahlberg <ronniesahlberg@...il.com>,
	Chuck Lever <chuck.lever@...cle.com>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Steve French <sfrench@...ba.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-cifs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/4] fs: Add FS_XFLAG_COMPRESSED & FS_XFLAG_ENCRYPTED
 for FS_IOC_FS[GS]ETXATTR API

On Tue, Feb 18, 2025 at 08:27:01PM +0100, Pali Rohár wrote:
> On Tuesday 18 February 2025 10:13:46 Amir Goldstein wrote:
> > > and there is no need for whacky field
> > > masks or anything like that. All it needs is a single bit to
> > > indicate if the windows attributes are supported, and they are all
> > > implemented as normal FS_XFLAG fields in the fsx_xflags field.
> > >
> 
> If MS adds 3 new attributes then we cannot add them to fsx_xflags
> because all bits of fsx_xflags would be exhausted.

And then we can discuss how to extend the fsxattr structure to
implement more flags.

In this scenario we'd also need another flag bit to indicate that
there is a second set of windows attributes that are supported...

i.e. this isn't a problem we need to solve right now.

> Just having only one FS_XFLAGS_HAS_WIN_ATTRS flag for determining windows
> attribute support is not enough, as it would not say anything useful for
> userspace.

IDGI.

That flag is only needed to tell userspace "this filesystem supports
windows attributes". Then GET will return the ones that are set,
and SET will return -EINVAL for those that it can't set (e.g.
compress, encrypt). What more does userspace actually need?

-Dave.
-- 
Dave Chinner
david@...morbit.com