linux-kernel - RE: [PATCH 3/4] char/tpm: Improve a size determination in nine functions

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Date:   Wed, 18 Oct 2017 09:16:12 +0000
From:   <Alexander.Steffen@...ineon.com>
To:     <julia.lawall@...6.fr>, <zohar@...ux.vnet.ibm.com>
CC:     <linux-kernel@...r.kernel.org>, <kernel-janitors@...r.kernel.org>,
        <andriy.shevchenko@...ux.intel.com>,
        <elfring@...rs.sourceforge.net>, <linux-integrity@...r.kernel.org>,
        <linuxppc-dev@...ts.ozlabs.org>, <benh@...nel.crashing.org>,
        <clabbe.montjoie@...il.com>, <jarkko.sakkinen@...ux.intel.com>,
        <jgunthorpe@...idianresearch.com>, <jsnitsel@...hat.com>,
        <kgold@...ux.vnet.ibm.com>, <mpe@...erman.id.au>,
        <nayna@...ux.vnet.ibm.com>, <paulus@...ba.org>,
        <PeterHuewe@....de>, <stefanb@...ux.vnet.ibm.com>
Subject: RE: [PATCH 3/4] char/tpm: Improve a size determination in nine
 functions

> On Tue, 17 Oct 2017, Mimi Zohar wrote:
> 
> > On Tue, 2017-10-17 at 14:58 +0200, Julia Lawall wrote:
> > >
> > > On Tue, 17 Oct 2017, Mimi Zohar wrote:
> > >
> > > > On Tue, 2017-10-17 at 11:50 +0000, Alexander.Steffen@...ineon.com
> > > > wrote:
> > > > > > > Replace the specification of data structures by pointer
> dereferences
> > > > > > > as the parameter for the operator "sizeof" to make the
> corresponding
> > > > > > > size
> > > > > > > determination a bit safer according to the Linux coding style
> > > > > > > convention.
> > > > > >
> > > > > >
> > > > > > This patch does one style in favor of the other.
> > > > >
> > > > > I actually prefer that style, so I'd welcome this change :)
> > > >
> > > > Style changes should be reviewed and documented, like any other
> code
> > > > change, and added to Documentation/process/coding-style.rst or an
> > > > equivalent file.
> > >
> > > Actually, it has been there for many years:
> > >
> > > 14) Allocating memory
> > > ---------------------
> > > ...
> > > The preferred form for passing a size of a struct is the following:
> > >
> > > .. code-block:: c
> > >
> > > 	p = kmalloc(sizeof(*p), ...);
> > >
> > > The alternative form where struct name is spelled out hurts readability
> and
> > > introduces an opportunity for a bug when the pointer variable type is
> changed
> > > but the corresponding sizeof that is passed to a memory allocator is not.
> >
> > True, thanks for the reminder.  Is this common in new code?  Is there
> > a script/ or some other automated way of catching this usage before
> > patches are upstreamed?
> >
> > Just as you're doing here, the patch description should reference this
> > in the patch description.
> 
> The comment in the documentation seems have been there since Linux
> 2.6.14,
> ie 2005.  The fact that a lot of code still doesn't use that style, 12
> years later, suggests that actually it is not preferred, or not preferred
> by everyone.  Perhaps the paragraph in coding style should just be
> dropped.

Or maybe everyone just copied existing code, which did not follow that pattern, because nobody bothered to fix old code ;-)

(This is true at least for tpm_tis_spi, where I was involved in its creation.)

Alexander