linux-kernel - Re: [PATCH 06/19] Add ioctl() argument and attribute handling utils

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Message-ID: <1833173750.1044971282356941800.JavaMail.root@zmail07.collab.prod.int.phx2.redhat.com>
Date:	Fri, 20 Aug 2010 22:15:41 -0400 (EDT)
From:	Miloslav Trmac <mitr@...hat.com>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	Herbert Xu <herbert@...dor.hengli.com.au>,
	linux-crypto@...r.kernel.org,
	Nikos Mavrogiannopoulos <n.mavrogiannopoulos@...il.com>,
	Neil Horman <nhorman@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/19] Add ioctl() argument and attribute handling utils

----- "Stefan Richter" <stefanr@...6.in-berlin.de> wrote:
> Miloslav Trmač wrote:
> > --- /dev/null
> > +++ b/crypto/userspace/utils.c
> [...]
> > +#ifdef CONFIG_COMPAT
> > +/* max() is too clever for compile-time constants */
> > +#define CONST_MAX(A, B) ((A) > (B) ? (A) : (B))
> > +
> > +#define MAX_SESSION_INPUT_DATA_SIZE					\
> > +	(CONST_MAX(sizeof(struct ncr_session_input_data),		\
> > +		   sizeof(struct compat_ncr_session_input_data)))
> > +#define MAX_SESSION_OUTPUT_BUFFER_SIZE					\
> > +	(CONST_MAX(sizeof(struct ncr_session_output_buffer),		\
> > +		   sizeof(struct compat_ncr_session_output_buffer)))
> > +
> > +#else /* !CONFIG_COMPAT */
> > +
> > +#define MAX_SESSION_INPUT_DATA_SIZE (sizeof(struct ncr_session_input_data))
> > +#define MAX_SESSION_OUTPUT_BUFFER_SIZE			\
> > +	(sizeof(struct ncr_session_output_buffer))
> > +
> > +#endif /* !CONFIG_COMPAT */
> 
> struct compat_xyz cannot be bigger than struct xyz, can it?
Perhaps not, but the code has been written and it's easier to keep it than to speculate :)  It also helps document the fact that the data format depends on properties of the userspace.
    Mirek
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