linux-ext4 - Re: [PATCH 1/4] fs: introduce SB

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Date:   Wed, 17 Jun 2020 20:19:35 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     Satya Tangirala <satyat@...gle.com>, linux-fsdevel@...r.kernel.org,
        linux-fscrypt@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH 1/4] fs: introduce SB_INLINECRYPT

On Thu, Jun 18, 2020 at 11:19:12AM +1000, Dave Chinner wrote:
> On Wed, Jun 17, 2020 at 07:57:29AM +0000, Satya Tangirala wrote:
> > Introduce SB_INLINECRYPT, which is set by filesystems that wish to use
> > blk-crypto for file content en/decryption. This flag maps to the
> > '-o inlinecrypt' mount option which multiple filesystems will implement,
> > and code in fs/crypto/ needs to be able to check for this mount option
> > in a filesystem-independent way.
> > 
> > Signed-off-by: Satya Tangirala <satyat@...gle.com>
> > ---
> >  fs/proc_namespace.c | 1 +
> >  include/linux/fs.h  | 1 +
> >  2 files changed, 2 insertions(+)
> > 
> > diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c
> > index 3059a9394c2d..e0ff1f6ac8f1 100644
> > --- a/fs/proc_namespace.c
> > +++ b/fs/proc_namespace.c
> > @@ -49,6 +49,7 @@ static int show_sb_opts(struct seq_file *m, struct super_block *sb)
> >  		{ SB_DIRSYNC, ",dirsync" },
> >  		{ SB_MANDLOCK, ",mand" },
> >  		{ SB_LAZYTIME, ",lazytime" },
> > +		{ SB_INLINECRYPT, ",inlinecrypt" },
> >  		{ 0, NULL }
> >  	};
> >  	const struct proc_fs_opts *fs_infop;
> 
> NACK.
> 
> SB_* flgs are for functionality enabled on the superblock, not for
> indicating mount options that have been set by the user.

That's an interesting claim, given that most SB_* flags are for mount options.
E.g.:

	ro => SB_RDONLY
	nosuid => SB_NOSUID
	nodev => SB_NODEV
	noexec => SB_NOEXEC
	sync => SB_SYNCHRONOUS
	mand => SB_MANDLOCK
	noatime => SB_NOATIME
	nodiratime => SB_NODIRATIME
	lazytime => SB_LAZYTIME

> 
> If the mount options are directly parsed by the filesystem option
> parser (as is done later in this patchset), then the mount option
> setting should be emitted by the filesystem's ->show_options
> function, not a generic function.
> 
> The option string must match what the filesystem defines, not
> require separate per-filesystem and VFS definitions of the same
> option that people could potentially get wrong (*cough* i_version vs
> iversion *cough*)....

Are you objecting to the use of a SB_* flag, or just to showing the flag in
show_sb_opts() instead of in the individual filesystems?  Note that the SB_*
flag was requested by Christoph
(https://lkml.kernel.org/r/20191031183217.GF23601@infradead.org/,
https://lkml.kernel.org/r/20191031212103.GA6244@infradead.org/).  We originally
used a function fscrypt_operations::inline_crypt_enabled() instead.

- Eric