[Xen-devel] Re: [PATCH] xen: add a comment for hypercall_xlat_continuation

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.11.11 at 08:57, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
> # HG changeset patch
> # User Ian Campbell <ian.campbell@xxxxxxxxxx>
> # Date 1320911800 0
> # Node ID 3c6eaf62996dd26d7d0a055955d30bc6c7067f91
> # Parent  e6af32ecb4483457d5ad9a7b674c18aaf20cc085
> xen: add a comment for hypercall_xlat_continuation
> 
> The interface of this function is really rather complex and having reverse
> engineered it for the N'th time I think it is time to write things down.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

Thanks for doing this!
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

> diff -r e6af32ecb448 -r 3c6eaf62996d xen/include/xen/compat.h
> --- a/xen/include/xen/compat.h        Tue Oct 18 14:15:09 2011 +0100
> +++ b/xen/include/xen/compat.h        Thu Nov 10 07:56:40 2011 +0000
> @@ -185,6 +185,34 @@ static inline int name(k xen_ ## n *x, k
>      CHECK_FIELD_COMMON_(k, CHECK_NAME_(k, n ## __ ## f1 ## __ ## f2 ## __ 
> ## \
>                                         f3, F2), n, f1.f2.f3)
>  
> +/*
> + * Translate a native continuation into a compat guest continuation.
> + *
> + * id: If non-NULL then points to an integer N between 0-5. Will be updated
> + * with the value of the N'th argument to the hypercall. The N'th argument 
> must
> + * not be subject to translation (i.e. cannot be referenced by @mask 
> below).
> + * This option is useful for extracting the "op" argument or similar from 
> the
> + * hypercall to enable further xlat processing.
> + *
> + * mask: Specifies which of the hypercall arguments require compat 
> translation.
> + * bit 0 indicates that the 0'th argument requires translation, bit 1 
> indicates
> + * that the first argument requires translation and so on. Native and 
> compat
> + * values for each translated argument are provided as @varargs (see 
> below).
> + *
> + * varargs: For each bit which is set in @mask the varargs contain a native
> + * value (unsigned long) and a compat value (unsigned int). If the native 
> value
> + * and compat value differ and the N'th argument is equal to the native 
> value
> + * then that argument is replaced by the compat value. If the native and 
> compat
> + * values are equal then no translation takes place. If the N'th argument 
> does
> + * not equal the native value then no translation takes place.
> + *
> + * Any untranslated argument (whether due to not being requested in @mask,
> + * native and compat values being equal or N'th argument not equalling 
> native
> + * value) must be equal in both native and compat representations (i.e. the
> + * native version cannot have any bits > 32 set)
> + *
> + * Return: Number of arguments which were actually translated.
> + */
>  int hypercall_xlat_continuation(unsigned int *id, unsigned int mask, ...);
>  
>  /* In-place translation functons: */




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