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hw/xen: Implement XenStore watches

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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>
This commit is contained in:
David Woodhouse 2023-01-22 18:38:23 +00:00
parent 3ef7ff83ca
commit 6e1330090d
2 changed files with 323 additions and 15 deletions
Download patch file Download diff file Expand all files Collapse all files

85
tests/unit/test-xs-node.c
View file

@ -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);
}