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Re: [PATCH 11/20] tools/xenstore: move changed domain handling



On 13.12.22 10:35, Julien Grall wrote:
Hi Juergen,

On 13/12/2022 06:53, Juergen Gross wrote:
On 01.12.22 22:58, Julien Grall wrote:
Hi Juergen,

On 01/11/2022 15:28, Juergen Gross wrote:
  static bool check_indexes(XENSTORE_RING_IDX cons, XENSTORE_RING_IDX prod)
@@ -492,8 +504,12 @@ static struct domain *find_or_alloc_existing_domain(unsigned int domid)
      xc_dominfo_t dominfo;
      domain = find_domain_struct(domid);
-    if (!domain && get_domain_info(domid, &dominfo))
-        domain = alloc_domain(NULL, domid);
+    if (!domain) {
+        if (!get_domain_info(domid, &dominfo))
+            errno = ENOENT;
+        else
+            domain = alloc_domain(NULL, domid);
+    }

I don't understand how this change is related to this commit.

It is directly related to the hunk below. Returning errno in
acc_add_dom_nbentry() requires it to be set correctly in
find_or_alloc_existing_domain().

I'll add a remark in the commit message.


[...]

+int acc_add_dom_nbentry(const void *ctx, struct list_head *head, int val,
+            unsigned int domid)
+{
+    struct changed_domain *cd;
+
+    cd = acc_get_changed_domain(ctx, head, domid);
+    if (!cd)
+        return errno;
+
+    cd->nbentry += val;

As a future improvement, it would be worth considering to check for underflow/overflow.

Do you really think we need to make sure not to add/remove more than
2 billion nodes owned by a single domain?
No and that's not my point. If you look at domain_entry_fix() we have an assert() to check if the sum is still over 0.

This assert() was actually triggered a few times while testing the previous XSAs batch. So I think it would be worth to carry a similar check (maybe not an assert()) just in case we mess up with accounting in the future.

Patch 2 of the 2nd series does that already.


Juergen

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