[RFC PATCH v3 3/3] tools/misc: Add xen-vcpus-stats tool

[Matias Ezequiel Vara Larsen <matiasevara@xxxxxxxxx>]

Add a demonstration tool that uses the stats_table resource to
query vcpus' RUNSTATE_running counter for a DomU.

Signed-off-by: Matias Ezequiel Vara Larsen <matias.vara@xxxxxxxx>
---
Changes in v3:
- use memory layout as discussed at
  https://lists.xenproject.org/archives/html/xen-devel/2023-03/msg00383.html
- use virt_*()
- issue xenforeignmemory_close()

Changes in v2:
- use period instead of frec
- rely on version to ensure reading is coherent 

Changes in v1:
- change the name of the tool to xen-vcpus-stats
- set command line parameters in the same order that are passed
- remove header libs.h
- build by default
- remove errno, strerrno, "\n", and identation
- use errx when errno is not needed
- address better the number of pages requested and error msgs
- use the shared_vcpustatspage_t structure
- use the correct frame id when requesting the resource
---
 tools/misc/Makefile          |   6 ++
 tools/misc/xen-vcpus-stats.c | 132 +++++++++++++++++++++++++++++++++++
 2 files changed, 138 insertions(+)
 create mode 100644 tools/misc/xen-vcpus-stats.c

diff --git a/tools/misc/Makefile b/tools/misc/Makefile
index 8b9558b93f..9c7cb50483 100644
--- a/tools/misc/Makefile
+++ b/tools/misc/Makefile
@@ -51,6 +51,7 @@ TARGETS_COPY += xenpvnetboot
 
 # Everything which needs to be built
 TARGETS_BUILD := $(filter-out $(TARGETS_COPY),$(TARGETS_ALL))
+TARGETS_BUILD += xen-vcpus-stats
 
 # ... including build-only targets
 TARGETS_BUILD += $(TARGETS_BUILD-y)
@@ -139,4 +140,9 @@ xencov: xencov.o
 xen-ucode: xen-ucode.o
        $(CC) $(LDFLAGS) -o $@ $< $(LDLIBS_libxenctrl) $(APPEND_LDFLAGS)
 
+xen-vcpus-stats.o: CFLAGS += $(CFLAGS_libxenforeginmemory)
+
+xen-vcpus-stats: xen-vcpus-stats.o
+       $(CC) $(LDFLAGS) -o $@ $< $(LDLIBS_libxenctrl) 
$(LDLIBS_libxenforeignmemory) $(APPEND_LDFLAGS)
+
 -include $(DEPS_INCLUDE)
diff --git a/tools/misc/xen-vcpus-stats.c b/tools/misc/xen-vcpus-stats.c
new file mode 100644
index 0000000000..f277b6ce8f
--- /dev/null
+++ b/tools/misc/xen-vcpus-stats.c
@@ -0,0 +1,132 @@
+#include <err.h>
+#include <errno.h>
+#include <error.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <signal.h>
+
+#include <xenctrl.h>
+#include <xenforeignmemory.h>
+#include <xen/vcpu.h>
+
+/*
+ * Note that virt_*() is used when ordering is required between the hypevisor
+ * and the tool domain. This tool is meant to be arch-agnostic so add the
+ * corresponding barrier for each architecture.
+ *
+ */
+#if defined(__x86_64__)
+#define barrier() asm volatile("" ::: "memory")
+#define virt_rmb() barrier()
+#elif defined(__aarch64__)
+#define dmb(opt) asm volatile("dmb " #opt : : : "memory")
+#define virt_rmb() dmb(ishld)
+#else
+#error Please fill in barrier macros
+#endif
+
+static sig_atomic_t interrupted;
+static void close_handler(int signum)
+{
+    interrupted = 1;
+}
+
+int main(int argc, char **argv)
+{
+    xenforeignmemory_handle *fh;
+    xenforeignmemory_resource_handle *res;
+    size_t size;
+    int rc, domid, period, vcpu;
+    xen_vcpu_shmemstats_t *info_shmem;
+    xen_shared_vcpustats_t *info;
+    struct sigaction act;
+    uint32_t seq;
+    uint64_t value;
+
+    if ( argc != 4 )
+    {
+        fprintf(stderr, "Usage: %s <domid> <vcpu> <period>\n", argv[0]);
+        return 1;
+    }
+
+    domid = atoi(argv[1]);
+    vcpu = atoi(argv[2]);
+    period = atoi(argv[3]);
+
+    act.sa_handler = close_handler;
+    act.sa_flags = 0;
+    sigemptyset(&act.sa_mask);
+    sigaction(SIGHUP,  &act, NULL);
+    sigaction(SIGTERM, &act, NULL);
+    sigaction(SIGINT,  &act, NULL);
+    sigaction(SIGALRM, &act, NULL);
+
+    fh = xenforeignmemory_open(NULL, 0);
+
+    if ( !fh )
+        err(1, "xenforeignmemory_open");
+
+    rc = xenforeignmemory_resource_size(
+        fh, domid, XENMEM_resource_stats_table,
+        XENMEM_resource_stats_table_id_vcpustats, &size);
+
+    if ( rc )
+        err(1, "Fail: Get size");
+
+    res = xenforeignmemory_map_resource(
+        fh, domid, XENMEM_resource_stats_table,
+        XENMEM_resource_stats_table_id_vcpustats, 0, size >> XC_PAGE_SHIFT,
+        (void **)&info_shmem, PROT_READ, 0);
+
+    if ( !res )
+        err(1, "Fail: Map");
+
+    if ( info_shmem->magic != VCPU_STATS_MAGIC )
+    {
+        fprintf(stderr, "Wrong magic number\n");
+        return 1;
+    }
+
+    if ( offsetof(struct vcpu_stats, runstate_running_time) > info_shmem->size 
)
+    {
+        fprintf(stderr, "The counter is not produced\n");
+        return 1;
+    }
+
+    info = (xen_shared_vcpustats_t*)((void*)info_shmem
+                                     + info_shmem->offset
+                                     + info_shmem->size * vcpu);
+
+    if ( info->runstate_running_time & ((uint64_t)1 << 63) )
+    {
+        fprintf(stderr, "The counter is inactived or has overflowed\n");
+        return 1;
+    }
+
+    while ( !interrupted )
+    {
+        sleep(period);
+        do {
+            seq = info[vcpu].seq;
+            virt_rmb();
+            value = info[vcpu].runstate_running_time;
+            virt_rmb();
+        } while ( (info[vcpu].seq & 1) ||
+                  (seq != info[vcpu].seq) );
+        if ( value & ((uint64_t)1 << 63) )
+            break;
+        printf("running_vcpu_time[%d]: %ld\n", vcpu, value);
+    }
+
+    rc = xenforeignmemory_unmap_resource(fh, res);
+    if ( rc )
+        err(1, "Fail: Unmap");
+
+    rc = xenforeignmemory_close(fh);
+    if ( rc )
+        err(1, "Fail: Close");
+
+    return 0;
+}
-- 
2.34.1