linux-kernel - Re: [PATCH 3/3] Add a pair of system calls to make extended file stats available [ver #2]

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Date:	Wed, 30 Jun 2010 13:14:10 +0100
From:	David Howells <dhowells@...hat.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	dhowells@...hat.com, viro@...iv.linux.org.uk, smfrench@...il.com,
	jlayton@...hat.com, mcao@...ibm.com,
	aneesh.kumar@...ux.vnet.ibm.com, linux-cifs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	samba-technical@...ts.samba.org, sjayaraman@...e.de,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/3] Add a pair of system calls to make extended file stats available [ver #2]

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

> Given a 64 bit flag word, you can start using bits for the version from
> the top and bits from the bottom for fields:

I suppose.  It's cleaner, though, to keep them separate.

> Alternatively, you can also make it a 64 bit argument everywhere, which has
> some other small disadvantages.

No, you can't.  32-bit systems can only pass 32-bit arguments.  If you're
suggesting passing a pointer to a 64-bit argument instead, how's that any
different from my suggestion of a separate parameter block?

> The idea of a syscall API with multiple fixed-length and variable-length
> fields in the same structure scares me. If you want to go this far,
> it may be better to base the interface on netlink and allow querying
> multiple files at once.

Urgh.  Netlink is way too much overhead and even scarier.  That's pretty much
a guarantee that people won't use it.  It also has to work if CONFIG_NET=n.

David
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