libxenlight: fix GC when cloning contexts

Provide a function to clone a context. This is necessary
because simply copying the structs will eventually
corrup the GC: maxsize is updated in the cloned context
but not in the originating, yet they have the same array
of referenced pointers alloc_ptrs.

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.com>

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 10ed0e06fdaf7747de0ee695ed9f460365c90b93..41010ef5df4d0a276ad9d7af0473f1446776a956 100644 (file)
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -656,10 +656,17 @@ void dm_xenstore_record_pid(struct libxl_ctx *ctx, void *for_spawn,
     struct libxl_device_model_starting *starting = for_spawn;
     struct libxl_ctx clone;
     char *kvs[3];
-    int rc;
-
-    clone = *ctx;
-    clone.xsh = xs_daemon_open();
+    int rc, cloned;
+
+    if (libxl_clone_context_xs(ctx, &clone)) {
+        XL_LOG(ctx, XL_LOG_ERROR, "Out of memory when cloning context");
+        /* Throw a prayer fallback */
+        clone = *ctx;
+        clone.xsh = xs_daemon_open();
+        cloned = 0;
+    } else {
+        cloned = 1;
+    }
     /* we mustn't use the parent's handle in the child */
 
     kvs[0] = "image/device-model-pid";
@@ -669,7 +676,11 @@ void dm_xenstore_record_pid(struct libxl_ctx *ctx, void *for_spawn,
     if (rc) XL_LOG_ERRNO(&clone, XL_LOG_ERROR,
                          "Couldn't record device model pid %ld at %s/%s",
                          (unsigned long)innerchild, starting->dom_path, kvs);
-    xs_daemon_close(clone.xsh);
+    if (cloned) {
+        libxl_discard_cloned_context_xs(&clone);
+    } else {
+        xs_daemon_close(clone.xsh);
+    }
 }
 
 static int libxl_vfb_and_vkb_from_device_model_info(struct libxl_ctx *ctx,

diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index eb54d344a951da5ec2206811f438fa78f7049528..16705f3b7ae17d839a004d95668fbdffec56bc57 100644 (file)
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -212,15 +212,19 @@ int libxl_devices_destroy(struct libxl_ctx *ctx, uint32_t domid, int force)
     fd_set rfds;
     struct timeval tv;
     flexarray_t *toremove;
-    struct libxl_ctx clone = *ctx;
+    struct libxl_ctx clone;
+
+    if (libxl_clone_context_xs(ctx, &clone)) {
+        XL_LOG(ctx, XL_LOG_ERROR, "Out of memory when cloning context");
+        return ERROR_NOMEM;
+    }
 
-    clone.xsh = xs_daemon_open();
     toremove = flexarray_make(16, 1);
     path = libxl_sprintf(&clone, "/local/domain/%d/device", domid);
     l1 = libxl_xs_directory(&clone, XBT_NULL, path, &num1);
     if (!l1) {
         XL_LOG(&clone, XL_LOG_ERROR, "%s is empty", path);
-        xs_daemon_close(clone.xsh);
+        libxl_discard_cloned_context_xs(&clone);
         return -1;
     }
     for (i = 0; i < num1; i++) {
@@ -269,7 +273,7 @@ int libxl_devices_destroy(struct libxl_ctx *ctx, uint32_t domid, int force)
         xs_rm(clone.xsh, XBT_NULL, path);
     }
     flexarray_free(toremove);
-    xs_daemon_close(clone.xsh);
+    libxl_discard_cloned_context_xs(&clone);
     return 0;
 }
 

diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c
index a04ac8ddf7decdf6598eaafd1c84fb351a4499df..eeadbfd71f44bde808df4020d65440f5fc8f7c72 100644 (file)
--- a/tools/libxl/libxl_internal.c
+++ b/tools/libxl/libxl_internal.c
@@ -28,6 +28,28 @@ int libxl_error_set(struct libxl_ctx *ctx, int code)
     return 0;
 }
 
+int libxl_clone_context(struct libxl_ctx *from, struct libxl_ctx *to)
+{
+    /* We could just copy the structs, but since
+     * maxsize is not a pointer we need to take care
+     * of our own GC. */
+    *to = *from;
+    to->alloc_ptrs = NULL;
+    to->alloc_maxsize = 256;
+    to->alloc_ptrs = calloc(to->alloc_maxsize, sizeof(void *));
+    if (!to->alloc_ptrs)
+        return ERROR_NOMEM;
+    return 0;
+}
+
+void libxl_discard_cloned_context(struct libxl_ctx *ctx)
+{
+    /* We only need to worry about GC-related fields */
+    (void)libxl_ctx_free(ctx);
+    if (ctx->alloc_ptrs)
+        free(ctx->alloc_ptrs);
+}
+
 int libxl_ptr_add(struct libxl_ctx *ctx, void *ptr)
 {
     int i;

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index a08821be343307dfd94712855d3757783985e67c..6aa98cae64df5bf9b943e1f4e72a6e53bb4fda2b 100644 (file)
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -63,6 +63,23 @@ typedef struct {
 #define PRINTF_ATTRIBUTE(x, y) __attribute__((format(printf, x, y)))
 
 /* memory allocation tracking/helpers */
+int libxl_clone_context(struct libxl_ctx *from, struct libxl_ctx *to);
+static inline int libxl_clone_context_xs(
+                struct libxl_ctx *from, struct libxl_ctx *to)
+{
+    int rc;
+    rc = libxl_clone_context(from, to);
+    if (rc) return rc;
+    to->xsh = xs_daemon_open();
+    return 0;
+}
+void libxl_discard_cloned_context(struct libxl_ctx *ctx);
+static inline void libxl_discard_cloned_context_xs(
+                struct libxl_ctx *ctx)
+{
+    libxl_discard_cloned_context(ctx);
+    xs_daemon_close(ctx->xsh);
+}
 int libxl_ptr_add(struct libxl_ctx *ctx, void *ptr);
 int libxl_free(struct libxl_ctx *ctx, void *ptr);
 int libxl_free_all(struct libxl_ctx *ctx);