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Date: Thu, 5 Jul 2012 21:33:43 +0300
From: Ilya Dryomov <idryomov@gmail.com>
To: Zach Brown <zab@zabbo.net>
Cc: Alexander Block <ablock84@googlemail.com>, linux-btrfs@vger.kernel.org
Subject: Re: [RFC PATCH 4/7] Btrfs: introduce subvol uuids and times
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On Thu, Jul 05, 2012 at 10:20:16AM -0700, Zach Brown wrote:
> On 07/05/2012 10:14 AM, Alexander Block wrote:
> >On Thu, Jul 5, 2012 at 7:08 PM, Zach Brown<zab@zabbo.net>  wrote:
> >>
> >>Careful, timespec will be different sizes in 32bit userspace and a 64bit
> >>kernel.  I'd use btrfs_timespec to get a fixed size timespec and avoid
> >>all the compat_timespec noise.  (I'd then also worry about padding and
> >>might pack the struct.. I always lose track of the best practice across
> >>all archs.)
> 
> >Hmm we currently don't have ctree.h in ioctl.h. Can I include it there
> >or are there problems with that? As an alternative I could define my
> >own struct for that.
> 
> Hmm, yeah, it looks like ioctl.h is well isolated and doesn't really
> have a precedent for pulling in format bits from the kernel
> implementation.
> 
> I'd do as you suggested and just make its own ioctl_timespec with a
> comment that its duplicating other similar structures to keep ioctl.h
> from getting tangled up in the kernel-side includes.

This has been done for restriper, see struct btrfs_balance_args vs
struct btrfs_disk_balance_args.  You could do the same thing:

struct btrfs_ioctl_timespec {
	__u64 sec;
	__u32 nsec;
} __attribute__ ((__packed__));

and take endianess into account with le{64,32}_to_cpu and
cpu_to_le{64,32} macros.

Thanks,

		Ilya