linux-kernel - Re: [PATCH net-next v7 01/19] lib/bitmap.c: conversion routines to/from u32 array

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Message-Id: <20160208153635.67df5ac2576138088a859087@linux-foundation.org>
Date:	Mon, 8 Feb 2016 15:36:35 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Decotigny <ddecotig@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ben Hutchings <ben@...adent.org.uk>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-api@...r.kernel.org, linux-mips@...ux-mips.org,
	fcoe-devel@...n-fcoe.org, Tejun Heo <tj@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Eugenia Emantayev <eugenia@...lanox.co.il>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Ido Shamay <idos@...lanox.com>, Joe Perches <joe@...ches.com>,
	Saeed Mahameed <saeedm@...lanox.com>,
	Govindarajulu Varadarajan <_govind@....com>,
	Venkata Duvvuru <VenkatKumar.Duvvuru@...lex.Com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Pravin B Shelar <pshelar@...ira.com>,
	Ed Swierk <eswierk@...portsystems.com>,
	Robert Love <robert.w.love@...el.com>,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	Yuval Mintz <Yuval.Mintz@...gic.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	David Decotigny <decot@...glers.com>
Subject: Re: [PATCH net-next v7 01/19] lib/bitmap.c: conversion routines
 to/from u32 array

On Sun,  7 Feb 2016 17:08:45 -0800 David Decotigny <ddecotig@...il.com> wrote:

> From: David Decotigny <decot@...glers.com>
> 
> Aimed at transferring bitmaps to/from user-space in a 32/64-bit agnostic
> way.
> 
> Tested:
>   unit tests (next patch) on qemu i386, x86_64, ppc, ppc64 BE and LE,
>   ARM.
> 
> @@ -1060,6 +1062,90 @@ int bitmap_allocate_region(unsigned long *bitmap, unsigned int pos, int order)
>  EXPORT_SYMBOL(bitmap_allocate_region);
>  
>  /**
> + * bitmap_from_u32array - copy the contents of a u32 array of bits to bitmap
> + *	@bitmap: array of unsigned longs, the destination bitmap, non NULL
> + *	@nbits: number of bits in @bitmap
> + *	@buf: array of u32 (in host byte order), the source bitmap, non NULL
> + *	@nwords: number of u32 words in @buf
> + *
> + * copy min(nbits, 32*nwords) bits from @buf to @bitmap, remaining
> + * bits between nword and nbits in @bitmap (if any) are cleared. In
> + * last word of @bitmap, the bits beyond nbits (if any) are kept
> + * unchanged.
> + */

This will leave the caller not knowing how many valid bits are actually
present in the resulting bitmap.  To determine that, the caller will
need to perform (duplicated) math on `nbits' and `nwords'.

> +void bitmap_from_u32array(unsigned long *bitmap, unsigned int nbits,
> +			  const u32 *buf, unsigned int nwords)

So how about we make this return the number of valid bits in *bitmap?

> +/**
> + * bitmap_to_u32array - copy the contents of bitmap to a u32 array of bits
> + *	@buf: array of u32 (in host byte order), the dest bitmap, non NULL
> + *	@nwords: number of u32 words in @buf
> + *	@bitmap: array of unsigned longs, the source bitmap, non NULL
> + *	@nbits: number of bits in @bitmap
> + *
> + * copy min(nbits, 32*nwords) bits from @bitmap to @buf. Remaining
> + * bits after nbits in @buf (if any) are cleared.
> + */
> +void bitmap_to_u32array(u32 *buf, unsigned int nwords,
> +			const unsigned long *bitmap, unsigned int nbits)

Ditto.