libxl_set_memory_target: retain the same maxmem offset on top of the current target

In libxl_set_memory_target when setting the new maxmem, retain the same
offset on top of the current target. In the future the offset will
include memory allocated by QEMU for rom files.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl.c

@@ -4676,11 +4676,16 @@ int libxl_set_memory_target(libxl_ctx *ctx, uint32_t domid,
     uint32_t current_max_memkb = 0;
     char *memmax, *endptr, *videoram_s = NULL, *target = NULL;
     char *dompath = libxl__xs_get_dompath(gc, domid);
-    xc_domaininfo_t info;
     libxl_dominfo ptr;
     char *uuid;
     xs_transaction_t t;
 
+    libxl_dominfo_init(&ptr);
+    if (libxl_domain_info(ctx, &ptr, domid) < 0)
+        goto out_no_transaction;
+
+    uuid = libxl__uuid2string(gc, ptr.uuid);
+
 retry_transaction:
     t = xs_transaction_start(ctx->xsh);
 
@@ -4756,13 +4761,12 @@ retry_transaction:
     }
 
     if (enforce) {
-        memorykb = new_target_memkb + videoram;
-        rc = xc_domain_setmaxmem(ctx->xch, domid, memorykb +
-                LIBXL_MAXMEM_CONSTANT);
+        memorykb = ptr.max_memkb - current_target_memkb + new_target_memkb;
+        rc = xc_domain_setmaxmem(ctx->xch, domid, memorykb);
         if (rc != 0) {
             LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR,
                     "xc_domain_setmaxmem domid=%d memkb=%d failed "
-                    "rc=%d\n", domid, memorykb + LIBXL_MAXMEM_CONSTANT, rc);
+                    "rc=%d\n", domid, memorykb, rc);
             abort_transaction = 1;
             goto out;
         }
@@ -4781,18 +4785,9 @@ retry_transaction:
 
     libxl__xs_write(gc, t, libxl__sprintf(gc, "%s/memory/target",
                 dompath), "%"PRIu32, new_target_memkb);
-    rc = xc_domain_getinfolist(ctx->xch, domid, 1, &info);
-    if (rc != 1 || info.domain != domid) {
-        abort_transaction = 1;
-        goto out;
-    }
 
-    libxl_dominfo_init(&ptr);
-    xcinfo2xlinfo(ctx, &info, &ptr);
-    uuid = libxl__uuid2string(gc, ptr.uuid);
     libxl__xs_write(gc, t, libxl__sprintf(gc, "/vm/%s/memory", uuid),
             "%"PRIu32, new_target_memkb / 1024);
-    libxl_dominfo_dispose(&ptr);
 
 out:
     if (!xs_transaction_end(ctx->xsh, t, abort_transaction)
@@ -4801,6 +4796,7 @@ out:
             goto retry_transaction;
 
 out_no_transaction:
+    libxl_dominfo_dispose(&ptr);
     GC_FREE;
     return rc;
 }