Re: [PATCH v1 2/5] libxc/trace: Add xc_tbuf_set_cpu_mask_array a variant of xc_tbuf_set_cpu_mask (v3)

[Ian Campbell <ian.campbell@citrix.com>]

On Wed, 2014-06-04 at 09:44 -0400, Konrad Rzeszutek Wilk wrote:
> which uses an xc_cpumap_t instead of a uint32_t. This means
> we can use an arbitrary bitmap without being limited to the
> 32-bits the xc_tbuf_set_cpu_mask_array can only do.

We do not guarantee API stability for libxc, so it is OK to either fix
the existing one or replace it. No need to keep the old one around
(unless perhaps calling applications fall into two sets each of whom
finds a different interface best).

> We also add an macro which can be used by both libxc and
> xentrace.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> [v2: Use DIV_ROUND_UP macro as suggested by Daniel]
> [v3: Use 'int' for bits instead of 'unsigned int' as spotted by Boris]
> ---
>  tools/libxc/xc_bitops.h |  2 ++
>  tools/libxc/xc_tbuf.c   | 40 ++++++++++++++++++++++++++++++++++++++++
>  tools/libxc/xenctrl.h   |  1 +
>  3 files changed, 43 insertions(+)
> 
> diff --git a/tools/libxc/xc_bitops.h b/tools/libxc/xc_bitops.h
> index d8e0c16..b8cf2bd 100644
> --- a/tools/libxc/xc_bitops.h
> +++ b/tools/libxc/xc_bitops.h
> @@ -12,6 +12,8 @@
>  #define BITMAP_ENTRY(_nr,_bmap) ((_bmap))[(_nr)/BITS_PER_LONG]
>  #define BITMAP_SHIFT(_nr) ((_nr) % BITS_PER_LONG)
>  
> +#define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))

This isn't really a bitops.h thing, xc_private.h seems like the usual
dumping ground for stuff which doesn't fit elsewhere.

> +int xc_tbuf_set_cpu_mask_array(xc_interface *xch, xc_cpumap_t mask, int bits)
> +{
> +    DECLARE_SYSCTL;
> +    DECLARE_HYPERCALL_BUFFER(uint8_t, bytemap);
> +    int ret = -1;
> +    int local_bits;
> +
> +    if ( bits <= 0 )
> +        goto out;
> +
> +    local_bits = xc_get_max_cpus(xch);
> +    if ( bits > local_bits )
> +    {
> +        PERROR("Wrong amount of bits supplied: %u, using %u\n", bits, local_bits);

Should we not just return an error?

> +        bits = local_bits;
> +    }
> +    bytemap = xc_hypercall_buffer_alloc(xch, bytemap, DIV_ROUND_UP(bits, 8));
> +    if ( bytemap == NULL )
> +    {
> +        PERROR("Could not allocate memory for xc_tbuf_set_cpu_mask_array hypercall");
> +        goto out;
> +    }
> +
> +    memcpy(bytemap, mask, DIV_ROUND_UP(bits, 8));

Take a look at Dario's "libxc: get and set soft and hard affinity"[0]
for how to do this using the hypercall bounce buffer interface.

[0] <1401237770-7003-6-git-send-email-dario.faggioli@citrix.com>

Ian.

> +
> +    sysctl.cmd = XEN_SYSCTL_tbuf_op;
> +    sysctl.interface_version = XEN_SYSCTL_INTERFACE_VERSION;
> +    sysctl.u.tbuf_op.cmd  = XEN_SYSCTL_TBUFOP_set_cpu_mask;
> +
> +    set_xen_guest_handle(sysctl.u.tbuf_op.cpu_mask.bitmap, bytemap);
> +    sysctl.u.tbuf_op.cpu_mask.nr_bits = bits;
> +
> +    ret = do_sysctl(xch, &sysctl);
> +
> +    xc_hypercall_buffer_free(xch, bytemap);
> +
> + out:
> +    return ret;
> +}
>  
>  int xc_tbuf_set_evt_mask(xc_interface *xch, uint32_t mask)
>  {