hw/xen: Implement XenStore watches

Starts out fairly simple: a hash table of watches based on the path.

Except there can be multiple watches on the same path, so the watch ends
up being a simple linked list, and the head of that list is in the hash
table. Which makes removal a bit of a PITA but it's not so bad; we just
special-case "I had to remove the head of the list and now I have to
replace it in / remove it from the hash table". And if we don't remove
the head, it's a simple linked-list operation.

We do need to fire watches on *deleted* nodes, so instead of just a simple
xs_node_unref() on the topmost victim, we need to recurse down and fire
watches on them all.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

1 files changed, 85 insertions, 0 deletions

diff --git a/tests/unit/test-xs-node.c b/tests/unit/test-xs-node.c
index c78d5bd..19000b6 100644
--- a/tests/unit/test-xs-node.c
+++ b/tests/unit/test-xs-node.c
@@ -34,10 +34,14 @@ static void xs_impl_delete(XenstoreImplState *s)
 {
     int err;
 
+    xs_impl_reset_watches(s, DOMID_GUEST);
+    g_assert(!s->nr_domu_watches);
+
     err = xs_impl_rm(s, DOMID_QEMU, XBT_NULL, "/local");
     g_assert(!err);
     g_assert(s->nr_nodes == 1);
 
+    g_hash_table_unref(s->watches);
     xs_node_unref(s->root);
     g_free(s);
 
@@ -65,6 +69,14 @@ static int write_str(XenstoreImplState *s, unsigned int dom_id,
     return err;
 }
 
+static void watch_cb(void *_str, const char *path, const char *token)
+{
+    GString *str = _str;
+
+    g_string_append(str, path);
+    g_string_append(str, token);
+}
+
 static XenstoreImplState *setup(void)
 {
    XenstoreImplState *s = xs_impl_create();
@@ -75,6 +87,7 @@ static XenstoreImplState *setup(void)
 
    err = write_str(s, DOMID_QEMU, XBT_NULL, abspath, "");
    g_assert(!err);
+   g_assert(s->nr_nodes == 4);
 
    g_free(abspath);
 
@@ -93,6 +106,8 @@ static void test_xs_node_simple(void)
 {
     GByteArray *data = g_byte_array_new();
     XenstoreImplState *s = setup();
+    GString *guest_watches = g_string_new(NULL);
+    GString *qemu_watches = g_string_new(NULL);
     GList *items = NULL;
     XsNode *old_root;
     uint64_t gencnt;
@@ -100,6 +115,20 @@ static void test_xs_node_simple(void)
 
     g_assert(s);
 
+    err = xs_impl_watch(s, DOMID_GUEST, "some", "guestwatch",
+                        watch_cb, guest_watches);
+    g_assert(!err);
+    g_assert(guest_watches->len == strlen("someguestwatch"));
+    g_assert(!strcmp(guest_watches->str, "someguestwatch"));
+    g_string_truncate(guest_watches, 0);
+
+    err = xs_impl_watch(s, 0, "/local/domain/1/some", "qemuwatch",
+                        watch_cb, qemu_watches);
+    g_assert(!err);
+    g_assert(qemu_watches->len == strlen("/local/domain/1/someqemuwatch"));
+    g_assert(!strcmp(qemu_watches->str, "/local/domain/1/someqemuwatch"));
+    g_string_truncate(qemu_watches, 0);
+
     /* Read gives ENOENT when it should */
     err = xs_impl_read(s, DOMID_GUEST, XBT_NULL, "foo", data);
     g_assert(err == ENOENT);
@@ -109,6 +138,14 @@ static void test_xs_node_simple(void)
                     "something");
     g_assert(s->nr_nodes == 7);
     g_assert(!err);
+    g_assert(!strcmp(guest_watches->str,
+                     "some/relative/pathguestwatch"));
+    g_assert(!strcmp(qemu_watches->str,
+                     "/local/domain/1/some/relative/pathqemuwatch"));
+
+    g_string_truncate(qemu_watches, 0);
+    g_string_truncate(guest_watches, 0);
+    xs_impl_reset_watches(s, 0);
 
     /* Read gives back what we wrote */
     err = xs_impl_read(s, DOMID_GUEST, XBT_NULL, "some/relative/path", data);
@@ -123,6 +160,8 @@ static void test_xs_node_simple(void)
     g_assert(!err);
     g_assert(data->len == strlen("something"));
 
+    g_assert(!qemu_watches->len);
+    g_assert(!guest_watches->len);
     /* Keep a copy, to force COW mode */
     old_root = xs_node_ref(s->root);
 
@@ -132,12 +171,18 @@ static void test_xs_node_simple(void)
                     "something else");
     g_assert(!err);
     g_assert(s->nr_nodes == 8);
+    g_assert(!qemu_watches->len);
+    g_assert(!strcmp(guest_watches->str, "some/relative/path2guestwatch"));
+    g_string_truncate(guest_watches, 0);
 
     /* Overwrite an existing node */
     err = write_str(s, DOMID_GUEST, XBT_NULL, "some/relative/path",
                     "another thing");
     g_assert(!err);
     g_assert(s->nr_nodes == 8);
+    g_assert(!qemu_watches->len);
+    g_assert(!strcmp(guest_watches->str, "some/relative/pathguestwatch"));
+    g_string_truncate(guest_watches, 0);
 
     /* We can list the two files we wrote */
     err = xs_impl_directory(s, DOMID_GUEST, XBT_NULL, "some/relative", &gencnt,
@@ -151,9 +196,38 @@ static void test_xs_node_simple(void)
     g_assert(!items->next->next);
     g_list_free_full(items, g_free);
 
+    err = xs_impl_unwatch(s, DOMID_GUEST, "some", "guestwatch",
+                          watch_cb, guest_watches);
+    g_assert(!err);
+
+    err = xs_impl_unwatch(s, DOMID_GUEST, "some", "guestwatch",
+                          watch_cb, guest_watches);
+    g_assert(err == ENOENT);
+
+    err = xs_impl_watch(s, DOMID_GUEST, "some/relative/path2", "watchp2",
+                        watch_cb, guest_watches);
+    g_assert(!err);
+    g_assert(guest_watches->len == strlen("some/relative/path2watchp2"));
+    g_assert(!strcmp(guest_watches->str, "some/relative/path2watchp2"));
+    g_string_truncate(guest_watches, 0);
+
+    err = xs_impl_watch(s, DOMID_GUEST, "/local/domain/1/some/relative",
+                        "watchrel", watch_cb, guest_watches);
+    g_assert(!err);
+    g_assert(guest_watches->len ==
+             strlen("/local/domain/1/some/relativewatchrel"));
+    g_assert(!strcmp(guest_watches->str,
+                     "/local/domain/1/some/relativewatchrel"));
+    g_string_truncate(guest_watches, 0);
+
     /* Write somewhere else which already existed */
     err = write_str(s, DOMID_GUEST, XBT_NULL, "some/relative", "moredata");
     g_assert(!err);
+    g_assert(s->nr_nodes == 8);
+
+    g_assert(!strcmp(guest_watches->str,
+                     "/local/domain/1/some/relativewatchrel"));
+    g_string_truncate(guest_watches, 0);
 
     g_byte_array_set_size(data, 0);
     err = xs_impl_read(s, DOMID_GUEST, XBT_NULL, "some/relative", data);
@@ -164,6 +238,7 @@ static void test_xs_node_simple(void)
     /* Overwrite existing data */
     err = write_str(s, DOMID_GUEST, XBT_NULL, "some/relative", "otherdata");
     g_assert(!err);
+    g_string_truncate(guest_watches, 0);
 
     g_byte_array_set_size(data, 0);
     err = xs_impl_read(s, DOMID_GUEST, XBT_NULL, "some/relative", data);
@@ -176,11 +251,21 @@ static void test_xs_node_simple(void)
     g_assert(!err);
     g_assert(s->nr_nodes == 5);
 
+    /* Each watch fires with the least specific relevant path */
+    g_assert(strstr(guest_watches->str,
+                    "some/relative/path2watchp2"));
+    g_assert(strstr(guest_watches->str,
+                    "/local/domain/1/some/relativewatchrel"));
+    g_string_truncate(guest_watches, 0);
+
     g_byte_array_set_size(data, 0);
     err = xs_impl_read(s, DOMID_GUEST, XBT_NULL, "some/relative", data);
     g_assert(err == ENOENT);
     g_byte_array_unref(data);
 
+    xs_impl_reset_watches(s, DOMID_GUEST);
+    g_string_free(qemu_watches, true);
+    g_string_free(guest_watches, true);
     xs_node_unref(old_root);
     xs_impl_delete(s);
 }