Re: [Xen-devel] [PATCH v6 07/11] xen: introduce rangeset_consume_ranges

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Sep 19, 2017 at 04:29:32PM +0100, Roger Pau Monne wrote:
> This function allows to iterate over a rangeset while removing the
> processed regions.
> 
> It will be used by the following patches in order to store memory
> regions in rangesets, and remove them while iterating.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Tim Deegan <tim@xxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
> Changes since v5:
>  - New in this version.
> ---
>  xen/common/rangeset.c      | 28 ++++++++++++++++++++++++++++
>  xen/include/xen/rangeset.h |  4 ++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/xen/common/rangeset.c b/xen/common/rangeset.c
> index 6c6293c15c..fd4a6b3384 100644
> --- a/xen/common/rangeset.c
> +++ b/xen/common/rangeset.c
> @@ -298,6 +298,34 @@ int rangeset_report_ranges(
>      return rc;
>  }

I think you need to document the behaviour of this new function due to
its destructive nature.

Something like:

Iterate through the range within a range set. Call cb on each range
provided. Bail on first error. Destroy the range processed when cb
has consumed the whole range.

Though without reading further I don't know why cb will only consume
part of the range but not all of it all the time.

>  
> +int rangeset_consume_ranges(
> +    struct rangeset *r,
> +    int (*cb)(unsigned long s, unsigned long e, void *, unsigned long *c),
> +    void *ctxt)
> +{
> +    int rc = 0;
> +
> +    write_lock(&r->lock);
> +    while ( !rangeset_is_empty(r) )
> +    {
> +        unsigned long consumed = 0;
> +        struct range *x = first_range(r);
> +
> +        rc = cb(x->s, x->e, ctxt, &consumed);
> +
> +        ASSERT(consumed <= x->e - x->s + 1);
> +        x->s += consumed;
> +        if ( x->s > x->e )
> +            destroy_range(r, x);
> +
> +        if ( rc )
> +            break;
> +    }
> +    write_unlock(&r->lock);
> +
> +    return rc;
> +}
> +
>  int rangeset_add_singleton(
>      struct rangeset *r, unsigned long s)
>  {
> diff --git a/xen/include/xen/rangeset.h b/xen/include/xen/rangeset.h
> index aa6408248b..dfdb193800 100644
> --- a/xen/include/xen/rangeset.h
> +++ b/xen/include/xen/rangeset.h
> @@ -67,6 +67,10 @@ bool_t __must_check rangeset_overlaps_range(
>  int rangeset_report_ranges(
>      struct rangeset *r, unsigned long s, unsigned long e,
>      int (*cb)(unsigned long s, unsigned long e, void *), void *ctxt);
> +int rangeset_consume_ranges(
> +    struct rangeset *r,
> +    int (*cb)(unsigned long s, unsigned long e, void *, unsigned long *c),
> +    void *ctxt);
>  
>  /* Add/remove/query a single number. */
>  int __must_check rangeset_add_singleton(
> -- 
> 2.11.0 (Apple Git-81)
> 

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