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

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Message-ID: <3868.1537742717@warthog.procyon.org.uk>
Date:   Sun, 23 Sep 2018 23:45:17 +0100
From:   David Howells <dhowells@...hat.com>
To:     Christian Brauner <christian@...uner.io>
Cc:     dhowells@...hat.com, Miklos Szeredi <mszeredi@...hat.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] fsmount: do not use legacy MS_ flags

Christian Brauner <christian@...uner.io> wrote:

> Of course, I'm not sure what the reasons for all of the other arguments to
> this function are since it's not yet implemented.

Well, dfd, path and atflags are pretty standard.  atflags conveys things like
AT_EMPTY_PATH or AT_SYMLINK_NOFOLLOW and dfd conveys a file descriptor
pointing to a vfs object or AT_FDCWD.

> Seems that attr_values and attr_mask could be compacted to a single
> attr_mask maybe?

If you don't have a mask, you can't really do recursion.  Without the mask,
you have to supply the entire set of options absolutely - and this would get
stamped on everything in the target range.

With a mask in combination with the set of desired values, you can turn on or
off a specific subset of the attributes without affecting the rest - without
needing to know the rest.

David