[PATCHv2 0/4] Add "xl info" command

[PATCHv2 0/4] Add "xl info" command

[Andre Przywara]

The "info" subcommand is missing from the xl tool.
The attached patchset adds support for this, extending libxl on the way
to provide the necessary info only by using own functions.
On my system the output of xm info and xl info was identical, I omitted
the recent NUMA additions from xl info for now and will provide the
necessary patches later.

Reworked version due to comments from Ian and Vincent (thanks for the review!)
Changes to version 1:
- use Xen public headers for constants instead of (re-)defining them
- comment the meaning of the return value of get_sched_id()
- remove the masking feature for get_version_info
- make the version_info structure a member of libxl_ctx and fill it
  on demand, omitting the need to free it manually

Please apply!

Regards,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 488-3567-12

[PATCHv2 1/4] libxl: extend physinfo structure

[Andre Przywara]

The libxl version of the physinfo sysctl does not contain some
fields like nr_nodes or capabilities needed for xl info output.
Add them to the structure and the retrieving function.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
---
 tools/libxl/libxl.c |    4 ++++
 tools/libxl/libxl.h |    4 ++++
 2 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index f1fe35d..1ef4325 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -2344,6 +2344,10 @@ int libxl_get_physinfo(struct libxl_ctx *ctx, struct libxl_physinfo *physinfo)
     physinfo->total_pages = xcphysinfo.total_pages;
     physinfo->free_pages = xcphysinfo.free_pages;
     physinfo->scrub_pages = xcphysinfo.scrub_pages;
+    physinfo->nr_nodes = xcphysinfo.nr_nodes;
+    memcpy(physinfo->hw_cap,xcphysinfo.hw_cap, sizeof(physinfo->hw_cap));
+    physinfo->phys_cap = xcphysinfo.capabilities;
+
     return 0;
 }
 
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 6236059..8b9d869 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -426,6 +426,10 @@ struct libxl_physinfo {
     uint64_t total_pages;
     uint64_t free_pages;
     uint64_t scrub_pages;
+
+    uint32_t nr_nodes;
+    uint32_t hw_cap[8];
+    uint32_t phys_cap;
 };
 
 int libxl_get_physinfo(struct libxl_ctx *ctx, struct libxl_physinfo *physinfo);
-- 
1.6.4

[PATCHv2 2/4] libxl: add sched_get_id function

[Andre Przywara]

To get the name of the currently used scheduler, Xen provides a
sched_id sysctl.
Add a libxl wrapper around the libxc function to query this.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
---
 tools/libxl/libxl.c |   13 +++++++++++++
 tools/libxl/libxl.h |    2 ++
 2 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 1ef4325..3db4249 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -2421,3 +2421,16 @@ int libxl_set_vcpucount(struct libxl_ctx *ctx, uint32_t domid, uint32_t count)
     }
     return 0;
 }
+
+/*
+ * returns one of the XEN_SCHEDULER_* constants from public/domctl.h
+ * or -1 if an error occured.
+ */
+int libxl_get_sched_id(struct libxl_ctx *ctx)
+{
+    int sched, ret;
+
+    if ((ret = xc_sched_id(ctx->xch, &sched)) != 0)
+        return ret;
+    return sched;
+}
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 8b9d869..b079613 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -438,5 +438,7 @@ struct libxl_vcpuinfo *libxl_list_vcpu(struct libxl_ctx *ctx, uint32_t domid,
 int libxl_set_vcpuaffinity(struct libxl_ctx *ctx, uint32_t domid, uint32_t vcpuid,
                            uint64_t *cpumap, int cpusize);
 int libxl_set_vcpucount(struct libxl_ctx *ctx, uint32_t domid, uint32_t count);
+
+int libxl_get_sched_id(struct libxl_ctx *ctx);
 #endif /* LIBXL_H */
 
-- 
1.6.4

[PATCHv2 3/4] libxl: add version_info function

[Andre Przywara]

Xen provides a xen_version hypercall to query the values of several
interesting things (like hypervisor version, commandline used, actual
changeset, etc.). Create a user-friendly and efficient wrapper around
the libxc function to provide values for xl info output.
Since the information is static during the whole runtime, we store
it within the libxl_ctx structure and just deliver the pointer on
subsequent calls.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
---
 tools/libxl/libxl.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
 tools/libxl/libxl.h |   18 ++++++++++++++++++
 2 files changed, 64 insertions(+), 0 deletions(-)

diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index b079613..0d3b767 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -41,6 +41,21 @@ struct libxl_vminfo {
     uint32_t domid;
 };
 
+typedef struct {
+    int xen_version_major;
+    int xen_version_minor;
+    char *xen_version_extra;
+    char *compiler;
+    char *compile_by;
+    char *compile_domain;
+    char *compile_date;
+    char *capabilities;
+    char *changeset;
+    unsigned long virt_start;
+    unsigned long pagesize;
+    char *commandline;
+} libxl_version_info;
+
 struct libxl_ctx {
     int xch;
     struct xs_handle *xsh;
@@ -56,8 +71,11 @@ struct libxl_ctx {
      * set this after libxl_init and before any other call - or
      * may leave them untouched */
     int (*waitpid_instead)(pid_t pid, int *status, int flags);
+    libxl_version_info version_info;
 };
 
+const libxl_version_info* libxl_get_version_info(struct libxl_ctx *ctx);
+
 typedef struct {
     bool hvm;
     bool hap;
diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 3db4249..2e8d621 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -45,6 +45,7 @@ int libxl_ctx_init(struct libxl_ctx *ctx, int version)
     ctx->alloc_ptrs = calloc(ctx->alloc_maxsize, sizeof(void *));
     if (!ctx->alloc_ptrs)
         return ERROR_NOMEM;
+    memset(&ctx->version_info, 0, sizeof(libxl_version_info));
 
     ctx->xch = xc_interface_open();
     if (ctx->xch == -1) {
@@ -2351,6 +2352,51 @@ int libxl_get_physinfo(struct libxl_ctx *ctx, struct libxl_physinfo *physinfo)
     return 0;
 }
 
+const libxl_version_info* libxl_get_version_info(struct libxl_ctx *ctx)
+{
+    union {
+        xen_extraversion_t xen_extra;
+        xen_compile_info_t xen_cc;
+        xen_changeset_info_t xen_chgset;
+        xen_capabilities_info_t xen_caps;
+        xen_platform_parameters_t p_parms;
+        xen_commandline_t xen_commandline;
+    } u;
+    long xen_version;
+    libxl_version_info *info = &ctx->version_info;
+
+    if (info->xen_version_extra != NULL)
+        return info;
+
+    xen_version = xc_version(ctx->xch, XENVER_version, NULL);
+    info->xen_version_major = xen_version >> 16;
+    info->xen_version_minor = xen_version & 0xFF;
+    xc_version(ctx->xch, XENVER_extraversion, &u.xen_extra);
+    info->xen_version_extra = libxl_sprintf(ctx, u.xen_extra);
+
+    xc_version(ctx->xch, XENVER_compile_info, &u.xen_cc);
+    info->compiler = libxl_sprintf(ctx, u.xen_cc.compiler);
+    info->compile_by = libxl_sprintf(ctx, u.xen_cc.compile_by);
+    info->compile_domain = libxl_sprintf(ctx, u.xen_cc.compile_domain);
+    info->compile_date = libxl_sprintf(ctx, u.xen_cc.compile_date);
+
+    xc_version(ctx->xch, XENVER_capabilities, &u.xen_caps);
+    info->capabilities = libxl_sprintf(ctx, u.xen_caps);
+
+    xc_version(ctx->xch, XENVER_changeset, &u.xen_chgset);
+    info->changeset = libxl_sprintf(ctx, u.xen_chgset);
+
+    xc_version(ctx->xch, XENVER_platform_parameters, &u.p_parms);
+    info->virt_start = u.p_parms.virt_start;
+
+    info->pagesize = xc_version(ctx->xch, XENVER_pagesize, NULL);
+
+    xc_version(ctx->xch, XENVER_commandline, &u.xen_commandline);
+    info->commandline = libxl_sprintf(ctx, u.xen_commandline);
+
+    return info;
+}
+
 struct libxl_vcpuinfo *libxl_list_vcpu(struct libxl_ctx *ctx, uint32_t domid,
                                        int *nb_vcpu, int *cpusize)
 {
-- 
1.6.4

[PATCHv2 4/4] xl: add "xl info" command

[Andre Przywara]

The info subcommand was missing from the xl tool. Use the new libxl
wrapper functions to create a clone of "xm info". The splitting into
several smaller functions is enspired by the implementation in
XendNode.py.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
---
 tools/libxl/xl.c |  114 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 114 insertions(+), 0 deletions(-)

diff --git a/tools/libxl/xl.c b/tools/libxl/xl.c
index 1486a5e..e1cc529 100644
--- a/tools/libxl/xl.c
+++ b/tools/libxl/xl.c
@@ -30,6 +30,7 @@
 #include <sys/socket.h>
 #include <sys/select.h>
 #include <arpa/inet.h>
+#include <sys/utsname.h> /* for utsname in xl info */
 #include <xenctrl.h>
 #include <ctype.h>
 #include <inttypes.h>
@@ -2636,6 +2637,117 @@ int main_vcpuset(int argc, char **argv)
     exit(0);
 }
 
+static void output_xeninfo(void)
+{
+    const libxl_version_info *info;
+    int sched_id;
+
+    info = libxl_get_version_info(&ctx);
+    if ((sched_id = libxl_get_sched_id(&ctx)) < 0) {
+        fprintf(stderr, "get_sched_id sysctl failed.\n");
+        return;
+    }
+
+    printf("xen_major              : %d\n", info->xen_version_major);
+    printf("xen_minor              : %d\n", info->xen_version_minor);
+    printf("xen_extra              : %s\n", info->xen_version_extra);
+    printf("xen_caps               : %s\n", info->capabilities);
+    printf("xen_scheduler          : %s\n",
+        sched_id == XEN_SCHEDULER_SEDF ? "sedf" :
+        sched_id == XEN_SCHEDULER_CREDIT ? "credit" :
+        sched_id == XEN_SCHEDULER_CREDIT2 ? "credit2" : "unknown");
+    printf("xen_pagesize           : %lu\n", info->pagesize);
+    printf("platform_params        : virt_start=0x%lx\n", info->virt_start);
+    printf("xen_changeset          : %s\n", info->changeset);
+    printf("xen_commandline        : %s\n", info->commandline);
+    printf("cc_compiler            : %s\n", info->compiler);
+    printf("cc_compile_by          : %s\n", info->compile_by);
+    printf("cc_compile_domain      : %s\n", info->compile_domain);
+    printf("cc_compile_date        : %s\n", info->compile_date);
+
+    return;
+}
+
+static void output_nodeinfo(void)
+{
+    struct utsname utsbuf;
+
+    uname(&utsbuf);
+
+    printf("host                   : %s\n", utsbuf.nodename);
+    printf("release                : %s\n", utsbuf.release);
+    printf("version                : %s\n", utsbuf.version);
+    printf("machine                : %s\n", utsbuf.machine);
+
+    return;
+}
+
+static void output_physinfo(void)
+{
+    struct libxl_physinfo info;
+    const libxl_version_info *vinfo;
+    unsigned int i;
+
+    if (libxl_get_physinfo(&ctx, &info) != 0) {
+        fprintf(stderr, "libxl_physinfo failed.\n");
+        return;
+    }
+
+    printf("nr_cpus                : %d\n", info.nr_cpus);
+    printf("nr_nodes               : %d\n", info.nr_nodes);
+    printf("cores_per_socket       : %d\n", info.cores_per_socket);
+    printf("threads_per_core       : %d\n", info.threads_per_core);
+    printf("cpu_mhz                : %d\n", info.cpu_khz / 1000);
+    printf("hw_caps                : ");
+    for (i = 0; i < 8; i++)
+        printf("%08x%c", info.hw_cap[i], i < 7 ? ':' : '\n');
+    printf("virt_caps              :");
+    if (info.phys_cap & XEN_SYSCTL_PHYSCAP_hvm)
+        printf(" hvm");
+    if (info.phys_cap & XEN_SYSCTL_PHYSCAP_hvm_directio)
+        printf(" hvm_directio");
+    printf("\n");
+    vinfo = libxl_get_version_info(&ctx);
+    i = (1 << 20) / vinfo->pagesize;
+    printf("total_memory           : %lu\n", info.total_pages / i);
+    printf("free_memory            : %lu\n", info.free_pages / i);
+
+    return;
+}
+
+void info(int verbose)
+{
+    output_nodeinfo();
+
+    output_physinfo();
+
+    output_xeninfo();
+
+    printf("xend_config_format     : 4\n");
+
+    return;
+}
+
+void main_info(int argc, char **argv)
+{
+    int opt, verbose;
+
+    verbose = 0;
+    while ((opt = getopt(argc, argv, "h")) != -1) {
+        switch (opt) {
+        case 'h':
+            help("vcpu-list");
+            exit(0);
+        default:
+            fprintf(stderr, "option `%c' not supported.\n", opt);
+            break;
+        }
+    }
+
+    info(verbose);
+    exit(0);
+}
+
 int main(int argc, char **argv)
 {
     if (argc < 2) {
@@ -2696,6 +2808,8 @@ int main(int argc, char **argv)
         main_vcpupin(argc - 1, argv + 1);
     } else if (!strcmp(argv[1], "vcpu-set")) {
         main_vcpuset(argc - 1, argv + 1);
+    } else if (!strcmp(argv[1], "info")) {
+        main_info(argc - 1, argv + 1);
     } else if (!strcmp(argv[1], "help")) {
         if (argc > 2)
             help(argv[2]);
-- 
1.6.4

Re: [PATCHv2 0/4] Add "xl info" command

[Vincent Hanquez]

On 21/04/10 15:17, Andre Przywara wrote:
> The "info" subcommand is missing from the xl tool.
> The attached patchset adds support for this, extending libxl on the way
> to provide the necessary info only by using own functions.
> On my system the output of xm info and xl info was identical, I omitted
> the recent NUMA additions from xl info for now and will provide the
> necessary patches later.
>
> Reworked version due to comments from Ian and Vincent (thanks for the review!)
> Changes to version 1:
> - use Xen public headers for constants instead of (re-)defining them
> - comment the meaning of the return value of get_sched_id()
> - remove the masking feature for get_version_info
> - make the version_info structure a member of libxl_ctx and fill it
>    on demand, omitting the need to free it manually

all patches:

Acked-by: Vincent Hanquez <vincent.hanquez@eu.citrix.com>

Thanks for your contribution !

-- 
Vincent

Re: [PATCHv2 3/4] libxl: add version_info function

[Vincent Hanquez]

On 21/04/10 15:17, Andre Przywara wrote:
> +
> +    xc_version(ctx->xch, XENVER_commandline,&u.xen_commandline);
> +    info->commandline = libxl_sprintf(ctx, u.xen_commandline);

oh actually just missed that; it's important to not include a variable 
as the format string: if for some reason any of this field end up 
containing a %something, it will lead usually to segfault.

can you please replace all:

libxl_sprintf(ctx, ..);

by:

libxl_sprintf(ctx, "%s", ...);

Thanks,
-- 
Vincent

[PATCHv2a 3/4] libxl: add version_info function

[Andre Przywara]

Xen provides a xen_version hypercall to query the values of several
interesting things (like hypervisor version, commandline used, actual
changeset, etc.). Create a user-friendly and efficient wrapper around
the libxc function to provide values for xl info output.
Since the information is static during the whole runtime, we store
it within the libxl_ctx structure and just deliver the pointer on
subsequent calls.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
---
 tools/libxl/libxl.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
 tools/libxl/libxl.h |   18 ++++++++++++++++++
 2 files changed, 64 insertions(+), 0 deletions(-)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 3db4249..7cb3a1c 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -45,6 +45,7 @@ int libxl_ctx_init(struct libxl_ctx *ctx, int version)
     ctx->alloc_ptrs = calloc(ctx->alloc_maxsize, sizeof(void *));
     if (!ctx->alloc_ptrs)
         return ERROR_NOMEM;
+    memset(&ctx->version_info, 0, sizeof(libxl_version_info));
 
     ctx->xch = xc_interface_open();
     if (ctx->xch == -1) {
@@ -2351,6 +2352,51 @@ int libxl_get_physinfo(struct libxl_ctx *ctx, struct libxl_physinfo *physinfo)
     return 0;
 }
 
+const libxl_version_info* libxl_get_version_info(struct libxl_ctx *ctx)
+{
+    union {
+        xen_extraversion_t xen_extra;
+        xen_compile_info_t xen_cc;
+        xen_changeset_info_t xen_chgset;
+        xen_capabilities_info_t xen_caps;
+        xen_platform_parameters_t p_parms;
+        xen_commandline_t xen_commandline;
+    } u;
+    long xen_version;
+    libxl_version_info *info = &ctx->version_info;
+
+    if (info->xen_version_extra != NULL)
+        return info;
+
+    xen_version = xc_version(ctx->xch, XENVER_version, NULL);
+    info->xen_version_major = xen_version >> 16;
+    info->xen_version_minor = xen_version & 0xFF;
+    xc_version(ctx->xch, XENVER_extraversion, &u.xen_extra);
+    info->xen_version_extra = libxl_sprintf(ctx, "%s", u.xen_extra);
+
+    xc_version(ctx->xch, XENVER_compile_info, &u.xen_cc);
+    info->compiler = libxl_sprintf(ctx, "%s", u.xen_cc.compiler);
+    info->compile_by = libxl_sprintf(ctx, "%s", u.xen_cc.compile_by);
+    info->compile_domain = libxl_sprintf(ctx, "%s", u.xen_cc.compile_domain);
+    info->compile_date = libxl_sprintf(ctx, "%s", u.xen_cc.compile_date);
+
+    xc_version(ctx->xch, XENVER_capabilities, &u.xen_caps);
+    info->capabilities = libxl_sprintf(ctx, "%s", u.xen_caps);
+
+    xc_version(ctx->xch, XENVER_changeset, &u.xen_chgset);
+    info->changeset = libxl_sprintf(ctx, "%s", u.xen_chgset);
+
+    xc_version(ctx->xch, XENVER_platform_parameters, &u.p_parms);
+    info->virt_start = u.p_parms.virt_start;
+
+    info->pagesize = xc_version(ctx->xch, XENVER_pagesize, NULL);
+
+    xc_version(ctx->xch, XENVER_commandline, &u.xen_commandline);
+    info->commandline = libxl_sprintf(ctx, "%s", u.xen_commandline);
+
+    return info;
+}
+
 struct libxl_vcpuinfo *libxl_list_vcpu(struct libxl_ctx *ctx, uint32_t domid,
                                        int *nb_vcpu, int *cpusize)
 {
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index b079613..0d3b767 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -41,6 +41,21 @@ struct libxl_vminfo {
     uint32_t domid;
 };
 
+typedef struct {
+    int xen_version_major;
+    int xen_version_minor;
+    char *xen_version_extra;
+    char *compiler;
+    char *compile_by;
+    char *compile_domain;
+    char *compile_date;
+    char *capabilities;
+    char *changeset;
+    unsigned long virt_start;
+    unsigned long pagesize;
+    char *commandline;
+} libxl_version_info;
+
 struct libxl_ctx {
     int xch;
     struct xs_handle *xsh;
@@ -56,8 +71,11 @@ struct libxl_ctx {
      * set this after libxl_init and before any other call - or
      * may leave them untouched */
     int (*waitpid_instead)(pid_t pid, int *status, int flags);
+    libxl_version_info version_info;
 };
 
+const libxl_version_info* libxl_get_version_info(struct libxl_ctx *ctx);
+
 typedef struct {
     bool hvm;
     bool hap;
-- 
1.6.4

Re: [PATCHv2 3/4] libxl: add version_info function

[Andre Przywara]

Vincent Hanquez wrote:
> On 21/04/10 15:17, Andre Przywara wrote:
>> +
>> +    xc_version(ctx->xch, XENVER_commandline,&u.xen_commandline);
>> +    info->commandline = libxl_sprintf(ctx, u.xen_commandline);
> 
> oh actually just missed that; it's important to not include a variable 
> as the format string: if for some reason any of this field end up 
> containing a %something, it will lead usually to segfault.
Of course! I could tell you that I just wanted to know if someone will 
find this, but actually I was so keen on just replacing strdup with 
libxl_sprintf that I totally overlooked the changed semantic of the call.
 >
 > can you please replace all:
 >
 > libxl_sprintf(ctx, ..);
 >
 > by:
 >
 > libxl_sprintf(ctx, "%s", ...);
 >

Sure! Corrected patch follows!

Thanks for looking carefully!

Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 488-3567-12

Re: [PATCHv2 1/4] libxl: extend physinfo structure

[Paolo Bonzini]

On 04/21/2010 04:17 PM, Andre Przywara wrote:
> The libxl version of the physinfo sysctl does not contain some
> fields like nr_nodes or capabilities needed for xl info output.
> Add them to the structure and the retrieving function.

Vincent, Stefano, is it okay to break the ABI?

If so, I suggest adding an initial member to be filled with sizeof() of 
the structure, similar to many Win32 APIs like GetVersionEx.

http://msdn.microsoft.com/en-us/library/ms724451%28VS.85%29.aspx
http://msdn.microsoft.com/en-us/library/ms724834%28VS.85%29.aspx
http://msdn.microsoft.com/en-us/library/ms724833%28VS.85%29.aspx

Paolo

Re: [PATCHv2 1/4] libxl: extend physinfo structure

[Ian Jackson]

Paolo Bonzini writes ("Re: [PATCHv2 1/4] libxl: extend physinfo structure"):
> Vincent, Stefano, is it okay to break the ABI?

Yes, it is fine to break the ABI.

> If so, I suggest adding an initial member to be filled with sizeof() of 
> the structure, similar to many Win32 APIs like GetVersionEx.

We've basically decided we don't need to do that.  Libraries from
different major versions of Xen will not be ABI-compatible and will
have different sonames.  We intend that binaries linked to old
libraries will continue to work.

Ian.

Re: [PATCHv2 1/4] libxl: extend physinfo structure

[Ian Jackson]

I wrote:
> We've basically decided we don't need to do that.  Libraries from
> different major versions of Xen will not be ABI-compatible and will
> have different sonames.  We intend that binaries linked to old
> libraries will continue to work.

I mean, will continue to work _with the old library_ but the new
hypervisor/dom0.

Ian.

Re: [PATCHv2 1/4] libxl: extend physinfo structure

[Stefano Stabellini]

On Thu, 22 Apr 2010, Ian Jackson wrote:
> Paolo Bonzini writes ("Re: [PATCHv2 1/4] libxl: extend physinfo structure"):
> > Vincent, Stefano, is it okay to break the ABI?
> 
> Yes, it is fine to break the ABI.
> 
> > If so, I suggest adding an initial member to be filled with sizeof() of 
> > the structure, similar to many Win32 APIs like GetVersionEx.
> 
> We've basically decided we don't need to do that.  Libraries from
> different major versions of Xen will not be ABI-compatible and will
> have different sonames.  We intend that binaries linked to old
> libraries will continue to work.

Indeed.
We want to keep the library as simple as possible while providing all
the needed capabilities, and I think this simple schema provides just
that.