linux-kernel - Re: [PATCH 21/32] VFS: Implement fsmount() to effect a pre-configured mount [ver #8]

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Message-ID: <26748.1528125864@warthog.procyon.org.uk>
Date:   Mon, 04 Jun 2018 16:24:24 +0100
From:   David Howells <dhowells@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     dhowells@...hat.com, Al Viro <viro@...iv.linux.org.uk>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        linux-afs@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 21/32] VFS: Implement fsmount() to effect a pre-configured mount [ver #8]

Arnd Bergmann <arnd@...db.de> wrote:

> The prototype in the header doesn't match the one in the implementation,
> which should cause a compile-time error, at least if syscalls.h is included
> in namespace.c

I've fixed that sort of thing up from kbuild warnings.

> Do you have a particular use case in mind for the spare_4/spare_5 arguments?
> If not, we can probably skip them. If we end up needing them after all, we
> can always add a new syscall entry point, or use one of the flag bits to
> decide whether the additional arguments are valid or not.

Whilst that is true, these aren't really (or probably shouldn't be) hot path
syscalls, so I would contend that just clearing the extra arguments shouldn't
be much of a performance loss.  On the other hand, syscall numbers are to some
extent precious.  If we hit ~512 syscalls we start to have an issue as we
start to get overlaps.

And, yes, I do have ideas for them involving ID mapping on mounts (ie. killing
off shiftfs).

> >  COND_SYSCALL(sys_fsopen);
> > +COND_SYSCALL(sys_fsmount);
> 
> This should only be needed if the syscall is optional, which it doesn't
> seem to be (same for the other ones here).

Al removed them.

David