[Qemu-devel] [PATCH 1/2] vhost: add vhost_has_free_slot() interface

[Igor Mammedov <imammedo@redhat.com>]

it will allow for other parts of QEMU check if it's safe
to map memory region during hotplug/runtime.
That way hotplug path will have a chance to cancel
hotplug operation instead of crashing in vhost_commit().

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 hw/virtio/vhost-backend.c         | 23 ++++++++++++++++++++++-
 hw/virtio/vhost-user.c            |  8 +++++++-
 hw/virtio/vhost.c                 | 21 +++++++++++++++++++++
 include/hw/virtio/vhost-backend.h |  2 ++
 include/hw/virtio/vhost.h         |  1 +
 stubs/Makefile.objs               |  1 +
 stubs/vhost.c                     |  6 ++++++
 7 files changed, 60 insertions(+), 2 deletions(-)
 create mode 100644 stubs/vhost.c

diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
index 4d68a27..46fa707 100644
--- a/hw/virtio/vhost-backend.c
+++ b/hw/virtio/vhost-backend.c
@@ -11,6 +11,7 @@
 #include "hw/virtio/vhost.h"
 #include "hw/virtio/vhost-backend.h"
 #include "qemu/error-report.h"
+#include "linux/vhost.h"
 
 #include <sys/ioctl.h>
 
@@ -42,11 +43,31 @@ static int vhost_kernel_cleanup(struct vhost_dev *dev)
     return close(fd);
 }
 
+static int vhost_kernel_memslots_limit(struct vhost_dev *dev)
+{
+    int limit;
+    int s = offsetof(struct vhost_memory, regions);
+    struct vhost_memory *mem = g_malloc0(s);
+
+    assert(dev->mem->nregions);
+    do {
+        s += sizeof mem->regions[0];
+        mem = g_realloc(mem, s);
+        mem->regions[mem->nregions] = dev->mem->regions[0];
+        mem->nregions++;
+    } while (vhost_kernel_call(dev, VHOST_SET_MEM_TABLE, mem) != -1);
+    limit = mem->nregions - 1 > 0 ? mem->nregions - 1 : 0;
+    g_free(mem);
+
+    return limit;
+}
+
 static const VhostOps kernel_ops = {
         .backend_type = VHOST_BACKEND_TYPE_KERNEL,
         .vhost_call = vhost_kernel_call,
         .vhost_backend_init = vhost_kernel_init,
-        .vhost_backend_cleanup = vhost_kernel_cleanup
+        .vhost_backend_cleanup = vhost_kernel_cleanup,
+        .vhost_backend_memslots_limit = vhost_kernel_memslots_limit
 };
 
 int vhost_set_backend_type(struct vhost_dev *dev, VhostBackendType backend_type)
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index d6f2163..0487809 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -352,9 +352,15 @@ static int vhost_user_cleanup(struct vhost_dev *dev)
     return 0;
 }
 
+static int vhost_user_memslots_limit(struct vhost_dev *dev)
+{
+    return VHOST_MEMORY_MAX_NREGIONS;
+}
+
 const VhostOps user_ops = {
         .backend_type = VHOST_BACKEND_TYPE_USER,
         .vhost_call = vhost_user_call,
         .vhost_backend_init = vhost_user_init,
-        .vhost_backend_cleanup = vhost_user_cleanup
+        .vhost_backend_cleanup = vhost_user_cleanup,
+        .vhost_backend_memslots_limit = vhost_user_memslots_limit
         };
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 2712c6f..e964004 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -26,6 +26,18 @@
 
 static struct vhost_log *vhost_log;
 
+static int used_memslots;
+static int memslots_limit = -1;
+
+bool vhost_has_free_slot(void)
+{
+    if (memslots_limit >= 0) {
+        return memslots_limit > used_memslots;
+    }
+
+    return true;
+}
+
 static void vhost_dev_sync_region(struct vhost_dev *dev,
                                   MemoryRegionSection *section,
                                   uint64_t mfirst, uint64_t mlast,
@@ -457,6 +469,7 @@ static void vhost_set_memory(MemoryListener *listener,
     dev->mem_changed_start_addr = MIN(dev->mem_changed_start_addr, start_addr);
     dev->mem_changed_end_addr = MAX(dev->mem_changed_end_addr, start_addr + size - 1);
     dev->memory_changed = true;
+    used_memslots = dev->mem->nregions;
 }
 
 static bool vhost_section(MemoryRegionSection *section)
@@ -1119,6 +1132,14 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
     if (r < 0) {
         goto fail_features;
     }
+
+    r = hdev->vhost_ops->vhost_backend_memslots_limit(hdev);
+    if (memslots_limit > 0) {
+        memslots_limit = MIN(memslots_limit, r);
+    } else {
+        memslots_limit = r;
+    }
+
     r = hdev->vhost_ops->vhost_call(hdev, VHOST_SET_MEM_TABLE, hdev->mem);
     if (r < 0) {
         r = -errno;
diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
index e472f29..28b6714 100644
--- a/include/hw/virtio/vhost-backend.h
+++ b/include/hw/virtio/vhost-backend.h
@@ -24,12 +24,14 @@ typedef int (*vhost_call)(struct vhost_dev *dev, unsigned long int request,
              void *arg);
 typedef int (*vhost_backend_init)(struct vhost_dev *dev, void *opaque);
 typedef int (*vhost_backend_cleanup)(struct vhost_dev *dev);
+typedef int (*vhost_backend_memslots_limit)(struct vhost_dev *dev);
 
 typedef struct VhostOps {
     VhostBackendType backend_type;
     vhost_call vhost_call;
     vhost_backend_init vhost_backend_init;
     vhost_backend_cleanup vhost_backend_cleanup;
+    vhost_backend_memslots_limit vhost_backend_memslots_limit;
 } VhostOps;
 
 extern const VhostOps user_ops;
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index dd51050..17ff7b6 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -81,4 +81,5 @@ uint64_t vhost_get_features(struct vhost_dev *hdev, const int *feature_bits,
                             uint64_t features);
 void vhost_ack_features(struct vhost_dev *hdev, const int *feature_bits,
                         uint64_t features);
+bool vhost_has_free_slot(void);
 #endif
diff --git a/stubs/Makefile.objs b/stubs/Makefile.objs
index 9937a12..d2f1b21 100644
--- a/stubs/Makefile.objs
+++ b/stubs/Makefile.objs
@@ -38,3 +38,4 @@ stub-obj-$(CONFIG_WIN32) += fd-register.o
 stub-obj-y += cpus.o
 stub-obj-y += kvm.o
 stub-obj-y += qmp_pc_dimm_device_list.o
+stub-obj-y += vhost.o
diff --git a/stubs/vhost.c b/stubs/vhost.c
new file mode 100644
index 0000000..d346b85
--- /dev/null
+++ b/stubs/vhost.c
@@ -0,0 +1,6 @@
+#include "hw/virtio/vhost.h"
+
+bool vhost_has_free_slot(void)
+{
+    return true;
+}
-- 
1.8.3.1