[Xen-devel] [PATCH v2 4/6] libxl: allow creation of domains with a specified or random domid

[Paul Durrant <pdurrant@xxxxxxxxxx>]

This patch adds a 'domid' field to libxl_domain_create_info and then
modifies do_domain_create() to use that value if it is valid. Any valid
domid will be checked against the retired domid list before being passed
to libxl__domain_make().
If the domid value is invalid then Xen will choose the domid, as before,
unless the value is the new special RANDOM_DOMID value added to the API.
This value instructs libxl__domain_make() to select a random domid value,
check it for validity, verify it does not match a retired domain, and then
pass it to Xen's XEN_DOMCTL_createdomain operation. If Xen determines that
it co-incides with an existing domain, a new random value will be
selected and the operation will be re-tried.

NOTE: libxl__logv() is also modified to only log valid domid values in
      messages rather than any domid, valid or otherwise, that is not
      INVALID_DOMID.

Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
---
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Wei Liu <wl@xxxxxxx>
Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>

v2:
 - Re-worked to use a value from libxl_domain_create_info
---
 tools/libxl/libxl.h          |  9 +++++++++
 tools/libxl/libxl_create.c   | 32 +++++++++++++++++++++++++++++++-
 tools/libxl/libxl_internal.c |  2 +-
 tools/libxl/libxl_types.idl  |  1 +
 4 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 18c1a2d6bf..7e60ee1c8b 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -1268,6 +1268,14 @@ void libxl_mac_copy(libxl_ctx *ctx, libxl_mac *dst, 
const libxl_mac *src);
  */
 #define LIBXL_HAVE_DOMAIN_NEED_MEMORY_CONFIG
 
+/*
+ * LIBXL_HAVE_CREATEINFO_DOMID
+ *
+ * libxl_domain_create_new() and libxl_domain_create_restore() will use
+ * a domid specified in libxl_domain_create_info().
+ */
+#define LIBXL_HAVE_CREATEINFO_DOMID
+
 typedef char **libxl_string_list;
 void libxl_string_list_dispose(libxl_string_list *sl);
 int libxl_string_list_length(const libxl_string_list *sl);
@@ -1528,6 +1536,7 @@ int libxl_ctx_free(libxl_ctx *ctx /* 0 is OK */);
 /* domain related functions */
 
 #define INVALID_DOMID ~0
+#define RANDOM_DOMID (INVALID_DOMID - 1)
 
 /* If the result is ERROR_ABORTED, the domain may or may not exist
  * (in a half-created state).  *domid will be valid and will be the
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 1835a5502c..ee76dee364 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -600,9 +600,39 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config 
*d_config,
             goto out;
         }
 
-        ret = xc_domain_create(ctx->xch, domid, &create);
+        if (libxl_domid_valid_guest(info->domid)) {
+            *domid = info->domid;
+
+            if (libxl__is_retired_domid(gc, *domid)) {
+                LOGED(ERROR, *domid, "domain id is retired");
+                rc = ERROR_FAIL;
+                goto out;
+            }
+        } else if (info->domid == RANDOM_DOMID) {
+            *domid = 0; /* Zero-out initial value */
+        }
+
+        for (;;) {
+            if (info->domid == RANDOM_DOMID) {
+                /* Randomize lower order bytes */
+                ret = libxl__random_bytes(gc, (void *)domid,
+                                          sizeof(uint16_t));
+                if (ret < 0)
+                    break;
+
+                if (!libxl_domid_valid_guest(*domid) ||
+                    libxl__is_retired_domid(gc, *domid))
+                    continue;
+            }
+
+            ret = xc_domain_create(ctx->xch, domid, &create);
+            if (ret == 0 || errno != EEXIST || info->domid != RANDOM_DOMID)
+                break;
+        }
+
         if (ret < 0) {
             LOGED(ERROR, *domid, "domain creation fail");
+            *domid = INVALID_DOMID;
             rc = ERROR_FAIL;
             goto out;
         }
diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c
index ba5637358e..dc6aaa9c9f 100644
--- a/tools/libxl/libxl_internal.c
+++ b/tools/libxl/libxl_internal.c
@@ -234,7 +234,7 @@ void libxl__logv(libxl_ctx *ctx, xentoollog_level msglevel, 
int errnoval,
     fileline[sizeof(fileline)-1] = 0;
 
     domain[0] = 0;
-    if (domid != INVALID_DOMID)
+    if (libxl_domid_valid_guest(domid))
         snprintf(domain, sizeof(domain), "Domain %"PRIu32":", domid);
  x:
     xtl_log(ctx->lg, msglevel, errnoval, "libxl",
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 7921950f6a..d0d431614f 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -409,6 +409,7 @@ libxl_domain_create_info = Struct("domain_create_info",[
     ("ssidref",      uint32),
     ("ssid_label",   string),
     ("name",         string),
+    ("domid",        libxl_domid),
     ("uuid",         libxl_uuid),
     ("xsdata",       libxl_key_value_list),
     ("platformdata", libxl_key_value_list),
-- 
2.20.1


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