linux-kernel - Re: [PATCH 5/6] fsmount: do not use legacy MS

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Message-ID: <17157.1537542475@warthog.procyon.org.uk>
Date:   Fri, 21 Sep 2018 16:07:55 +0100
From:   David Howells <dhowells@...hat.com>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     dhowells@...hat.com, Al Viro <viro@...IV.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] fsmount: do not use legacy MS_ flags

Miklos Szeredi <mszeredi@...hat.com> wrote:

> What happens if we introduce new flags for fsmount(2) and are already out
> of flags for mount(2)?  I see a big mess that way.
> 
> So let's instead start a clean new set, to be used in the new API.

If we must.  But let's not call them just M_* please.  Let's call them
MOUNT_ATTR_* or something.

> The MS_RELATIME flag was accepted but ignored.  Simply leave this out of
> the new set, since "relatime" is the default.

Can we make RELATIME, STRICTATIME and NOATIME an enum rather than individual
flags?

	#define MOUNT_ATTR_RDONLY	0x01
	#define MOUNT_ATTR_NOSUID	0x02
	#define MOUNT_ATTR_NODEV	0x04
	#define MOUNT_ATTR_NOEXEC	0x08
	#define MOUNT_ATTR_RELATIME	0x00
	#define MOUNT_ATTR_NOATIME	0x10
	#define MOUNT_ATTR_STRICTATIME	0x20
	#define MOUNT_ATTR_ATIME_MASK	0x30
	#define MOUNT_ATTR_NODIRATIME	0x40

We can also use these for a mount_setattr() syscall:

	mount_setattr(int dfd, const char *path, unsigned int atflags,
		      unsigned int attr_values,
		      unsigned int attr_mask);

where atflags can potentially include AT_RECURSIVE.

David