The removed lines were initially added by commit 314e64084d31, but the
subsequent code which was using the nb_vm variable was later removed by
commit 2ba368d13893, which makes these lines of code an overlooked
reminiscence. Moreover, the call becomes very expensive when there is a
considerable number of VMs (~1000 instances) running on the host.

Signed-off-by: Costin Lupu <costin.lupu@cs.pub.ro>
---
 tools/libs/light/libxl_create.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/tools/libs/light/libxl_create.c b/tools/libs/light/libxl_create.c
index 0c64268f66..43e9ba9c63 100644
--- a/tools/libs/light/libxl_create.c
+++ b/tools/libs/light/libxl_create.c
@@ -578,7 +578,7 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config *d_config,
                        uint32_t *domid, bool soft_reset)
 {
     libxl_ctx *ctx = libxl__gc_owner(gc);
-    int ret, rc, nb_vm;
+    int ret, rc;
     const char *dom_type;
     char *uuid_string;
     char *dom_path, *vm_path, *libxl_path;
@@ -586,7 +586,6 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config *d_config,
     struct xs_permissions rwperm[1];
     struct xs_permissions noperm[1];
     xs_transaction_t t = 0;
-    libxl_vminfo *vm_list;
 
     /* convenience aliases */
     libxl_domain_create_info *info = &d_config->c_info;
@@ -869,14 +868,6 @@ retry_transaction:
                         ARRAY_SIZE(rwperm));
     }
 
-    vm_list = libxl_list_vm(ctx, &nb_vm);
-    if (!vm_list) {
-        LOGD(ERROR, *domid, "cannot get number of running guests");
-        rc = ERROR_FAIL;
-        goto out;
-    }
-    libxl_vminfo_list_free(vm_list, nb_vm);
-
     xs_write(ctx->xsh, t, GCSPRINTF("%s/uuid", vm_path), uuid_string, strlen(uuid_string));
     xs_write(ctx->xsh, t, GCSPRINTF("%s/name", vm_path), info->name, strlen(info->name));
 
-- 
2.20.1

On Mon, Apr 19, 2021 at 04:01:42PM +0300, Costin Lupu wrote:
> The removed lines were initially added by commit 314e64084d31, but the
> subsequent code which was using the nb_vm variable was later removed by
> commit 2ba368d13893, which makes these lines of code an overlooked
> reminiscence. Moreover, the call becomes very expensive when there is a
> considerable number of VMs (~1000 instances) running on the host.
> 

Nice catch.

> Signed-off-by: Costin Lupu <costin.lupu@cs.pub.ro>

Acked-by: Wei Liu <wl@xen.org>

> ---
>  tools/libs/light/libxl_create.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/tools/libs/light/libxl_create.c b/tools/libs/light/libxl_create.c
> index 0c64268f66..43e9ba9c63 100644
> --- a/tools/libs/light/libxl_create.c
> +++ b/tools/libs/light/libxl_create.c
> @@ -578,7 +578,7 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config *d_config,
>                         uint32_t *domid, bool soft_reset)
>  {
>      libxl_ctx *ctx = libxl__gc_owner(gc);
> -    int ret, rc, nb_vm;
> +    int ret, rc;
>      const char *dom_type;
>      char *uuid_string;
>      char *dom_path, *vm_path, *libxl_path;
> @@ -586,7 +586,6 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config *d_config,
>      struct xs_permissions rwperm[1];
>      struct xs_permissions noperm[1];
>      xs_transaction_t t = 0;
> -    libxl_vminfo *vm_list;
>  
>      /* convenience aliases */
>      libxl_domain_create_info *info = &d_config->c_info;
> @@ -869,14 +868,6 @@ retry_transaction:
>                          ARRAY_SIZE(rwperm));
>      }
>  
> -    vm_list = libxl_list_vm(ctx, &nb_vm);
> -    if (!vm_list) {
> -        LOGD(ERROR, *domid, "cannot get number of running guests");
> -        rc = ERROR_FAIL;
> -        goto out;
> -    }
> -    libxl_vminfo_list_free(vm_list, nb_vm);
> -
>      xs_write(ctx->xsh, t, GCSPRINTF("%s/uuid", vm_path), uuid_string, strlen(uuid_string));
>      xs_write(ctx->xsh, t, GCSPRINTF("%s/name", vm_path), info->name, strlen(info->name));
>  
> -- 
> 2.20.1
>