Re: [Xen-devel] [PATCH QEMU-XEN v4 7/9] xen: Use stable library interfaces when they are available.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 21 Oct 2015, Ian Campbell wrote:
> In Xen 4.7 we are refactoring parts libxenctrl into a number of
> separate libraries which will provide backward and forward API and ABI
> compatiblity.
> 
> Specifically libxenevtchn, libxengnttab and libxenforeignmemory.
> 
> Previous patches have already laid the groundwork for using these by
> switching the existing compatibility shims to reflect the intefaces to
> these libraries.
> 
> So all which remains is to update configure to detect the libraries
> and enable their use. Although they are notionally independent we take
> an all or nothing approach to the three libraries since they were
> added at the same time.
> 
> The only non-obvious bit is that we now open a proper xenforeignmemory
> handle for xen_fmem instead of reusing the xen_xc handle.
> 
> Build tested with 4.0, 4.5 and the patches targetting 4.7 which adds
> these libraries.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> ---
> v4: xenforeignmemory_open is now a compat wrapper, so no ifdef.
> 
>     Simplify configury by asserting that interface version 470 will
>     always have the libraries (lack of them makes it 460).
> 
>     Ran checkpatch and fixed everything except:
> 
> ERROR: need consistent spacing around '*' (ctx:WxV)
> +typedef xc_interface *XenXC;
> 
> Which I think is a false +ve.
> 
> simplify configury
> ---
>  configure                   | 55 
> +++++++++++++++++++++++++++++++++++++++++++++
>  include/hw/xen/xen_common.h | 38 +++++++++++++++++++++++++++++--
>  2 files changed, 91 insertions(+), 2 deletions(-)
> 
> diff --git a/configure b/configure
> index 779623a..fe0a39d 100755
> --- a/configure
> +++ b/configure
> @@ -1840,6 +1840,7 @@ fi
>  
>  if test "$xen" != "no" ; then
>    xen_libs="-lxenstore -lxenctrl -lxenguest"
> +  xen_stable_libs="-lxenforeignmemory -lxengnttab -lxenevtchn"
>  
>    # First we test whether Xen headers and libraries are available.
>    # If no, we are done and there is no Xen support.
> @@ -1862,6 +1863,57 @@ EOF
>    # Xen unstable
>    elif
>        cat > $TMPC <<EOF &&
> +/*
> + * If we have stable libs the we don't want the libxc compat
> + * layers, regardless of what CFLAGS we may have been given.
> + */
> +#undef XC_WANT_COMPAT_EVTCHN_API
> +#undef XC_WANT_COMPAT_GNTTAB_API
> +#undef XC_WANT_COMPAT_MAP_FOREIGN_API
> +#include <xenctrl.h>
> +#include <xenstore.h>
> +#include <xenevtchn.h>
> +#include <xengnttab.h>
> +#include <xenforeignmemory.h>
> +#include <stdint.h>
> +#include <xen/hvm/hvm_info_table.h>
> +#if !defined(HVM_MAX_VCPUS)
> +# error HVM_MAX_VCPUS not defined
> +#endif
> +int main(void) {
> +  xc_interface *xc;
> +  xenforeignmemory_handle *xfmem;
> +  xenevtchn_handle *xe;
> +  xengnttab_handle *xg;
> +
> +  xs_daemon_open();
> +
> +  xc = xc_interface_open(0, 0, 0);
> +  xc_hvm_set_mem_type(0, 0, HVMMEM_ram_ro, 0, 0);
> +  xc_domain_add_to_physmap(0, 0, XENMAPSPACE_gmfn, 0, 0);
> +  xc_hvm_inject_msi(xc, 0, 0xf0000000, 0x00000000);
> +  xc_hvm_create_ioreq_server(xc, 0, HVM_IOREQSRV_BUFIOREQ_ATOMIC, NULL);
> +
> +  xfmem = xenforeignmemory_open(0, 0);
> +  xenforeignmemory_map(xfmem, 0, 0, 0, 0, 0);
> +
> +  xe = xenevtchn_open(0, 0);
> +  xenevtchn_fd(xe);
> +
> +  xg = xengnttab_open(0, 0);
> +  xengnttab_map_grant_ref(xg, 0, 0, 0);
> +
> +  return 0;
> +}
> +EOF
> +      compile_prog "" "$xen_libs $xen_stable_libs"
> +  then
> +    xen_ctrl_version=470
> +    xen=yes

this is good


> +
> +  # Xen 4.6
> +  elif
> +      cat > $TMPC <<EOF &&
>  #include <xenctrl.h>
>  #include <xenstore.h>
>  #include <stdint.h>
> @@ -2037,6 +2089,9 @@ EOF
>    fi
>  
>    if test "$xen" = yes; then
> +    if test $xen_ctrl_version -ge 470  ; then
> +     libs_softmmu="$xen_stable_libs $libs_softmmu"

tab


> +    fi
>      libs_softmmu="$xen_libs $libs_softmmu"
>    fi
>  fi
> diff --git a/include/hw/xen/xen_common.h b/include/hw/xen/xen_common.h
> index 2a5f27a..38293b4 100644
> --- a/include/hw/xen/xen_common.h
> +++ b/include/hw/xen/xen_common.h
> @@ -6,6 +6,17 @@
>  #include <stddef.h>
>  #include <inttypes.h>
>  
> +#if CONFIG_XEN_CTRL_INTERFACE_VERSION >= 470
> +/*
> + * If we have new enough libxenctrl then we do not want/need these compat
> + * interfaces, despite what the user supplied cflags might say. They
> + * must be undefined before including xenctrl.h
> + */
> +#undef XC_WANT_COMPAT_EVTCHN_API
> +#undef XC_WANT_COMPAT_GNTTAB_API
> +#undef XC_WANT_COMPAT_MAP_FOREIGN_API
> +#endif

Can we always do the #under given that earlier libxenctrl versions will
simple ignore them?  I am asking because I would prefer to avoid
introducing another ifdef here outside the sequence if ifdefs already
present below.


>  #include <xenctrl.h>
>  #if CONFIG_XEN_CTRL_INTERFACE_VERSION < 420
>  #  include <xs.h>
> @@ -151,8 +162,8 @@ static inline void xs_close(struct xs_handle *xsh)
>  }
>  
>  
> -/* Xen 4.1 */
> -#else
> +/* Xen 4.1 thru 4.6 */
> +#elif CONFIG_XEN_CTRL_INTERFACE_VERSION < 470
>  
>  typedef xc_interface *XenXC;
>  typedef xc_interface *xenforeignmemory_handle;
> @@ -195,6 +206,29 @@ static inline int xc_fd(xc_interface *xen_xc)
>  {
>      return -1;
>  }
> +#else /* CONFIG_XEN_CTRL_INTERFACE_VERSION >= 470 */
> +
> +typedef xc_interface *XenXC;
> +
> +#  define XC_INTERFACE_FMT "%p"
> +#  define XC_HANDLER_INITIAL_VALUE    NULL
> +
> +#include <xenevtchn.h>
> +#include <xengnttab.h>
> +#include <xenforeignmemory.h>
> +
> +static inline XenXC xen_xc_interface_open(void *logger, void 
> *dombuild_logger,
> +                                          unsigned int open_flags)
> +{
> +    return xc_interface_open(logger, dombuild_logger, open_flags);
> +}
> +
> +/* FIXME There is now way to have the xen fd */
                     ^ no way

> +static inline int xc_fd(xc_interface *xen_xc)
> +{
> +    return -1;
> +}
> +
>  #endif
>  
>  /* Xen before 4.2 */
> -- 
> 2.1.4
> 

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