Re: [Xen-devel] [PATCH] fix xenctl_cpumap translation to handle bitops accessed like arrays

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 17/12/06 5:53 pm, "Jimi Xenidis" <jimix@xxxxxxxxxxxxxx> wrote:

> On PowerPC (and other big endian and/or RISC architectures) bit
> offsets in a bitmap are actually represented by a bit-offset from an
> element in an array rather than a bit-offset from the base memory
> pointer,  see xen/include/asm-powerpc/bitops.h for a complete
> explanation.
> 
> This complicates the conversion of cpumask_t from/to xenctl_cpumap.
> 
> The following patch allows an architecture to declare that bitops are
> "by long" rather than "by bit" and use an alternate scheme for
> encoding.

If the array-element type matters on big-endian systems then the tools
really need fixing: one libxc operation passes down a uint32_t unit; another
a uint64_t. Perhaps we should fix so they pass down 8-bit units (as the type
of xenctl_cpumap_t would suggest) and then we could have byte_to_long_bitmap
and long_to_byte_bitmap in Xen (which might encourage us to pull proper
endianness headers into Xen).

 -- Keir


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