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Re: [libvirt] [PATCH 1/2] libxl: expose multiple emulators per guest in the capabilities XML



David Scott wrote:
> libxl allows users to choose between two standard emulators:
> 1. (default in xen-4.2): qemu "traditional" (aka "qemu-dm")
> 2. (default in xen-4.3): qemu "upstream" (aka "qemu-system-i386")
>
> The person who builds and packages xen gets to choose which
> emulators are built. We examine the filesystem for the emulators
> at runtime and expose them as separate "domains" within the same
> "guest" architecture.
>
> Signed-off-by: David Scott <dave scott eu citrix com>
> ---
>  src/libxl/libxl_conf.c |   87 ++++++++++++++++++++++++++++++++++++-----------
>  1 files changed, 66 insertions(+), 21 deletions(-)
>
> diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
> index 7e0753a..472d116 100644
> --- a/src/libxl/libxl_conf.c
> +++ b/src/libxl/libxl_conf.c
> @@ -29,6 +29,8 @@
>  #include <libxl.h>
>  #include <sys/types.h>
>  #include <sys/socket.h>
> +#include <sys/stat.h>
> +#include <unistd.h>
>  
>  #include "internal.h"
>  #include "virlog.h"
> @@ -50,6 +52,28 @@
>  /* see xen-unstable.hg/xen/include/asm-x86/cpufeature.h */
>  #define LIBXL_X86_FEATURE_PAE_MASK 0x40
>  
> +enum emulator_type {
> +    emulator_traditional = 0,
> +    emulator_upstream    = 1,
> +    emulator_last        = 2,
> +    /* extend with specific qemu versions later */
> +};
>   

Do you think this will need to be extended in the future?  As
'qemu-traditional' goes by way of the Dodo, this won't be needed right?

> +
> +#define EMULATOR_LIB64 "/usr/lib64/xen/bin/"
> +#define EMULATOR_LIB32 "/usr/lib/xen/bin/"
> +
> +#define EMULATOR_TRADITIONAL "qemu-dm"
> +#define EMULATOR_UPSTREAM    "qemu-system-i386"
>   

I think this could be made quite a bit simpler with something like

#define LIBXL_EMULATOR_TRADITIONAL_PATH LIBDIR "/xen/bin/qemu-dm"
#define LIBXL_EMULATOR_UPSTREAM_PATH LIBDIR "/xen/bin/qemu-sytstem-i386"

> +
> +static const char* emulator_lib64_path [] = {
> +    EMULATOR_LIB64 EMULATOR_TRADITIONAL,
> +    EMULATOR_LIB64 EMULATOR_UPSTREAM,
> +};
> +
> +static const char* emulator_lib32_path [] = {
> +    EMULATOR_LIB32 EMULATOR_TRADITIONAL,
> +    EMULATOR_LIB32 EMULATOR_UPSTREAM,
> +};
>  
>  struct guest_arch {
>      virArch arch;
> @@ -68,10 +92,11 @@ static virCapsPtr
>  libxlBuildCapabilities(virArch hostarch,
>                         int host_pae,
>                         struct guest_arch *guest_archs,
> -                       int nr_guest_archs)
> +                       int nr_guest_archs,
> +                       int emulators_found[])
>  {
>      virCapsPtr caps;
> -    int i;
> +    int i, j;
>  
>      if ((caps = virCapabilitiesNew(hostarch, 1, 1)) == NULL)
>          goto no_memory;
> @@ -91,12 +116,8 @@ libxlBuildCapabilities(virArch hostarch,
>          if ((guest = virCapabilitiesAddGuest(caps,
>                                               guest_archs[i].hvm ? "hvm" : "xen",
>                                               guest_archs[i].arch,
> -                                             ((hostarch == VIR_ARCH_X86_64) ?
> -                                              "/usr/lib64/xen/bin/qemu-dm" :
> -                                              "/usr/lib/xen/bin/qemu-dm"),
> -                                             (guest_archs[i].hvm ?
> -                                              "/usr/lib/xen/boot/hvmloader" :
> -                                              NULL),
> +                                             NULL,
> +                                             NULL,
>                                               1,
>                                               machines)) == NULL) {
>              virCapabilitiesFreeMachines(machines, 1);
> @@ -104,13 +125,21 @@ libxlBuildCapabilities(virArch hostarch,
>          }
>          machines = NULL;
>  
> -        if (virCapabilitiesAddGuestDomain(guest,
> -                                          "xen",
> -                                          NULL,
> -                                          NULL,
> -                                          0,
> -                                          NULL) == NULL)
> -            goto no_memory;
> +        for (j = 0; j < emulator_last; ++j) {
> +            if (emulators_found[j] == -1) /* failure from stat(2) */
> +                continue;
> +            if (virCapabilitiesAddGuestDomain(guest,
> +                                              "xen",
> +                                              ((hostarch == VIR_ARCH_X86_64) ?
> +                                               emulator_lib64_path[j] :
> +                                               emulator_lib32_path[j]),
> +                                              (guest_archs[i].hvm ?
> +                                               "/usr/lib/xen/boot/hvmloader" :
> +                                               NULL),
> +                                              0,
> +                                              NULL) == NULL)
> +                goto no_memory;
> +        }
>   

and then just add the emulators here.  E.g.

if (virFileExists(LIBXL_EMULATOR_TRADITIONAL_PATH) {
    if (virCapabilitiesAddGuestDomain(guest,
                                      "xen",
                                      LIBXL_EMULATOR_TRADITIONAL_PATH
                                      (guest_archs[i].hvm ?
                                      "/usr/lib/xen/boot/hvmloader" :
                                      NULL),
                                      0,
                                      NULL) == NULL)
        goto no_memory;
}
if (virFileExists(LIBXL_EMULATOR_UPSTREAM_PATH) {
    if (virCapabilitiesAddGuestDomain(guest,
                                      "xen",
                                      LIBXL_EMULATOR_UPSTREAM_PATH
                                      (guest_archs[i].hvm ?
                                      "/usr/lib/xen/boot/hvmloader" :
                                      NULL),
                                      0,
                                      NULL) == NULL)
        goto no_memory;
}

                                     
Regards,
Jim

>  
>          if (guest_archs[i].pae &&
>              virCapabilitiesAddGuestFeature(guest,
> @@ -163,7 +192,8 @@ libxlBuildCapabilities(virArch hostarch,
>  static virCapsPtr
>  libxlMakeCapabilitiesInternal(virArch hostarch,
>                                libxl_physinfo *phy_info,
> -                              char *capabilities)
> +                              char *capabilities,
> +                              int emulators_found[])
>  {
>      char *str, *token;
>      regmatch_t subs[4];
> @@ -243,7 +273,7 @@ libxlMakeCapabilitiesInternal(virArch hostarch,
>                  continue;
>              }
>  
> -            /* Search for existing matching (model,hvm) tuple */
> +            /* Search for existing matching (arch,hvm) tuple */
>              for (i = 0 ; i < nr_guest_archs ; i++) {
>                  if ((guest_archs[i].arch == arch) &&
>                      guest_archs[i].hvm == hvm) {
> @@ -277,7 +307,8 @@ libxlMakeCapabilitiesInternal(virArch hostarch,
>      if ((caps = libxlBuildCapabilities(hostarch,
>                                         host_pae,
>                                         guest_archs,
> -                                       nr_guest_archs)) == NULL)
> +                                       nr_guest_archs,
> +                                       emulators_found)) == NULL)
>          goto no_memory;
>  
>      return caps;
> @@ -756,9 +787,13 @@ error:
>  virCapsPtr
>  libxlMakeCapabilities(libxl_ctx *ctx)
>  {
> -    int err;
> +    int i, err;
>      libxl_physinfo phy_info;
>      const libxl_version_info *ver_info;
> +    struct stat sbuf;
> +    const char *path;
> +    virArch hostarch;
> +    int emulators_found[emulator_last];
>  
>      err = regcomp(&xen_cap_rec, xen_cap_re, REG_EXTENDED);
>      if (err != 0) {
> @@ -782,9 +817,19 @@ libxlMakeCapabilities(libxl_ctx *ctx)
>          return NULL;
>      }
>  
> -    return libxlMakeCapabilitiesInternal(virArchFromHost(),
> +    hostarch = virArchFromHost();
> +
> +    for (i = 0; i < emulator_last; i++){
> +        path = (hostarch == VIR_ARCH_X86_64)?
> +                emulator_lib64_path[i]:
> +                emulator_lib32_path[i];
> +        emulators_found[i] = stat(path, &sbuf);
> +    }
> +
> +    return libxlMakeCapabilitiesInternal(hostarch,
>                                           &phy_info,
> -                                         ver_info->capabilities);
> +                                         ver_info->capabilities,
> +                                         emulators_found);
>  }
>  
>  int
>   


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