Re: [PATCH v2 07/19] tools/xenstore: introduce dummy nodes for special watch paths

[Juergen Gross]

On 20.12.22 20:39, Julien Grall wrote:

Hi Juergen,

On 13/12/2022 16:00, Juergen Gross wrote:

Instead of special casing the permission handling and watch event
firing for the special watch paths "@introduceDomain" and
"@releaseDomain", use static dummy nodes added to the data base when
starting Xenstore.

The node accounting needs to reflect that change by adding the special
nodes in the domain_entry_fix() call in setup_structure().

Note that this requires to rework the calls of fire_watches() for the
special events in order to avoid leaking memory.

Move the check for a valid node name from get_node() to
get_node_canonicalized(), as it allows to use get_node() for the
special nodes, too.

In order to avoid read and write accesses to the special nodes use a
special variant for obtaining the current node data for the permission
handling.

This allows to simplify quite some code. In future sub-nodes of the
special nodes will be possible due to this change, allowing more fine
grained permission control of special events for specific domains.

Signed-off-by: Juergen Gross <jgr...@suse.com>
---
V2:
- add get_spec_node()
- expand commit message (Julien Grall)
---
  tools/xenstore/xenstored_control.c |   3 -
  tools/xenstore/xenstored_core.c    |  92 +++++++++-------
  tools/xenstore/xenstored_domain.c  | 162 ++++-------------------------
  tools/xenstore/xenstored_domain.h  |   6 --
  tools/xenstore/xenstored_watch.c   |  17 +--
  5 files changed, 80 insertions(+), 200 deletions(-)


index d1aaa00bf4..41e6992591 100644
--- a/tools/xenstore/xenstored_control.c
+++ b/tools/xenstore/xenstored_control.c

      if (ret)
          goto out;
      ret = dump_state_connections(fp);
-    if (ret)
-        goto out;
-    ret = dump_state_special_nodes(fp);
      if (ret)
          goto out;
      ret = dump_state_nodes(fp, ctx);
diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 1650821922..f96714e1b8 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c

  static unsigned int get_acc_domid(struct connection *conn, TDB_DATA *key,
                    unsigned int domid)
  {
-    return (!conn || key->dptr[0] == '/') ? domid : conn->id;
+    return (!conn || key->dptr[0] == '/' || key->dptr[0] == '@')

diff --git a/tools/xenstore/xenstored_control.c b/tools/xenstore/xenstored_control.c @@ -676,9 +676,6 @@ static const char *lu_dump_state(const void *ctx, struct connection *conn) @@ -616,7 +616,8 @@ static void get_acc_data(TDB_DATA *key, struct node_account_data *acc)

The comment on top of get_acc_domid() needs to be updated.

Oh, yes.

+           ? domid : conn->id;
  }

[...]

+static void fire_special_watches(const char *name)
+{
+    void *ctx = talloc_new(NULL);
+    struct node *node;
+
+    if (!ctx)
+        return;
+
+    node = read_node(NULL, ctx, name);
+
+    if (node)
+        fire_watches(NULL, ctx, name, node, true, NULL);

NIT: I would consider to log an error (maybe only once) if 'node' is NULL. The purpose is to help debugging Xenstored.

I think we can log it always, as this is really a bad problem.


Juergen

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