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

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Message-ID: <20250216183432.GA2404@sol.localdomain>
Date: Sun, 16 Feb 2025 10:34:32 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: Pali Rohár <pali@...nel.org>
Cc: Amir Goldstein <amir73il@...il.com>,
	"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 Sun, Feb 16, 2025 at 05:40:26PM +0100, Pali Rohár wrote:
> This allows to get or set FS_COMPR_FL and FS_ENCRYPT_FL bits via FS_IOC_FSGETXATTR/FS_IOC_FSSETXATTR API.
> 
> Signed-off-by: Pali Rohár <pali@...nel.org>

Does this really allow setting FS_ENCRYPT_FL via FS_IOC_FSSETXATTR, and how does
this interact with the existing fscrypt support in ext4, f2fs, ubifs, and ceph
which use that flag?  In the fscrypt case it's very intentional that
FS_ENCRYPT_FL can be gotten via FS_IOC_GETFLAGS but not set via FS_IOC_SETFLAGS.
A simple toggle of the flag can't work, as it doesn't provide the needed
information.  Instead there is a separate ioctl (FS_IOC_SET_ENCRYPTION_POLICY)
for enabling encryption which takes additional parameters and only works on
empty directories.

- Eric