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Re: [Qemu-block] [PATCH 05/18] xen: add xenstore watcher infratructure
From: |
Anthony PERARD |
Subject: |
Re: [Qemu-block] [PATCH 05/18] xen: add xenstore watcher infratructure |
Date: |
Mon, 3 Dec 2018 14:42:31 +0000 |
User-agent: |
Mutt/1.11.0 (2018-11-25) |
On Wed, Nov 21, 2018 at 03:11:58PM +0000, Paul Durrant wrote:
> A Xen PV frontend communicates its state to the PV backend by writing to
> the 'state' key in the frontend area in xenstore. It is therefore
> necessary for a XenDevice implementation to be notified whenever the
> value of this key changes.
>
> This patch adds code to do this as follows:
>
> - an 'fd handler' is registered on the libxenstore handle which will be
> triggered whenever a 'watch' event occurs
> - primitives are added to xen-bus-helper to add or remove watch events
> - a list of Notifier objects is added to XenBus to provide a mechanism
> to call the appropriate 'watch handler' when its associated event
> occurs
>
> The xen-qisk implementation is extended with a 'frontend_changed' method,
"The xen-qdisk"
> which calls as-yet stub 'connect' and 'disconnect' functions when the
> relevant frontend state transitions occur. A subsequent patch will supply
> a full implementation for these functions.
>
> Signed-off-by: Paul Durrant <address@hidden>
> ---
> diff --git a/hw/block/xen-qdisk.c b/hw/block/xen-qdisk.c
> index 0859643f7d..35f7b70480 100644
> --- a/hw/block/xen-qdisk.c
> +++ b/hw/block/xen-qdisk.c
> +static void xen_qdisk_frontend_changed(XenDevice *xendev,
> + enum xenbus_state frontend_state,
> + Error **errp)
> +{
> + XenQdiskDevice *qdiskdev = XEN_QDISK_DEVICE(xendev);
> + enum xenbus_state backend_state = xen_device_backend_get_state(xendev);
> + Error *local_err = NULL;
> +
> + switch (frontend_state) {
> + case XenbusStateInitialised:
> + case XenbusStateConnected:
> + if (backend_state == XenbusStateConnected) {
> + break;
> + }
> +
> + xen_qdisk_disconnect(qdiskdev, &error_fatal);
Do we want to crash (actually exit) QEMU when disconnect failed?
> + xen_qdisk_connect(qdiskdev, &local_err);
> + if (local_err) {
> + error_propagate(errp, local_err);
> + break;
> + }
> +
> + xen_device_backend_set_state(xendev, XenbusStateConnected);
> + break;
> +
> + case XenbusStateClosing:
> + xen_device_backend_set_state(xendev, XenbusStateClosing);
> + break;
> +
> + case XenbusStateClosed:
> + xen_qdisk_disconnect(qdiskdev, &error_fatal);
> + xen_device_backend_set_state(xendev, XenbusStateClosed);
> + break;
> +
> + default:
> + break;
> + }
> +}
> +
> diff --git a/hw/xen/xen-bus-helper.c b/hw/xen/xen-bus-helper.c
> index d9ee2ed6a0..b44acc8047 100644
> --- a/hw/xen/xen-bus-helper.c
> +++ b/hw/xen/xen-bus-helper.c
> @@ -122,3 +122,31 @@ int xs_node_scanf(struct xs_handle *xsh, const char
> *node, const char *key,
>
> return rc;
> }
> +
> +void xs_node_watch(struct xs_handle *xsh, const char *node, const char *key,
> + char *token, Error **errp)
> +{
> + char *path;
> +
> + path = (strlen(node) != 0) ? g_strdup_printf("%s/%s", node, key) :
> + g_strdup(key);
> +
> + if (!xs_watch(xsh, path, token)) {
> + error_setg_errno(errp, errno, "failed to watch path '%s'", path);
> + }
> +
> + g_free(path);
> +}
> +
> +void xs_node_unwatch(struct xs_handle *xsh, const char *node,
> + const char *key, const char *token)
> +{
> + char *path;
> +
> + path = (strlen(node) != 0) ? g_strdup_printf("%s/%s", node, key) :
> + g_strdup(key);
> +
> + xs_unwatch(xsh, path, token);
I think we should check for error from xs_unwatch as well.
> +
> + g_free(path);
> +}
> diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
> index 663aa8e117..99988f8568 100644
> --- a/hw/xen/xen-bus.c
> +++ b/hw/xen/xen-bus.c
> +static XenWatch *xen_bus_add_watch(XenBus *xenbus, const char *node,
> + const char *key, XenWatchHandler handler,
> + void *opaque, Error **errp)
> +{
> + XenWatch *watch = g_new0(XenWatch, 1);
> + QemuUUID uuid;
> + Error *local_err = NULL;
> +
> + qemu_uuid_generate(&uuid);
> + watch->token = qemu_uuid_unparse_strdup(&uuid);
> +
> + trace_xen_bus_add_watch(node, key, watch->token);
> +
> + watch->node = g_strdup(node);
> + watch->key = g_strdup(key);
> + watch->handler = handler;
> + watch->opaque = opaque;
> + watch->notifier.notify = watch_notify;
> +
> + notifier_list_add(&xenbus->watch_notifiers, &watch->notifier);
> +
> + xs_node_watch(xenbus->xsh, node, key, watch->token, &local_err);
> +
> + if (local_err) {
> + error_propagate(errp, local_err);
> +
> + notifier_remove(&watch->notifier);
> +
> + g_free(watch->token);
> + g_free(watch->key);
> + g_free(watch->node);
> +
> + g_free(watch);
It would be better to have a function that will free/dispose of a
XenWatch, or maybe simply calling xen_bus_remove_watch here might be
enough.
> + watch = NULL;
You could return NULL instead.
> + }
> +
> + return watch;
> +}
> +
> +static void xen_bus_remove_watch(XenBus *xenbus, XenWatch *watch)
> +{
> + trace_xen_bus_remove_watch(watch->node, watch->key, watch->token);
> +
> + xs_node_unwatch(xenbus->xsh, watch->node, watch->key, watch->token);
> +
> + notifier_remove(&watch->notifier);
> +
> + g_free(watch->token);
> + g_free(watch->key);
> + g_free(watch->node);
> +
> + g_free(watch);
> +}
> +static void xen_bus_watch(void *opaque)
> +{
> + XenBus *xenbus = opaque;
> + char **v;
> + const char *token;
> + unsigned int n;
> +
> + g_assert(xenbus->xsh);
> +
> + v = xs_read_watch(xenbus->xsh, &n);
What is the n for?
Also, maybe you wanted to call xs_check_watch instead? (In a loop, until
EGAIN)
> + if (!v) {
> + return;
> + }
> +
> + token = v[XS_WATCH_TOKEN];
> +
> + trace_xen_bus_watch(token);
> +
> + notifier_list_notify(&xenbus->watch_notifiers, (void *)token);
> +
> + free(v);
> +}
> +
> static void xen_bus_realize(BusState *bus, Error **errp)
> {
> XenBus *xenbus = XEN_BUS(bus);
> @@ -230,12 +419,24 @@ static void xen_device_frontend_create(XenDevice
> *xendev, Error **errp)
> error_propagate(errp, local_err);
> error_prepend(errp, "failed to create frontend: ");
> }
> +
> + xendev->frontend_state_watch =
> + xen_bus_add_watch(xenbus, xendev->frontend_path, "state",
> + xen_device_frontend_changed, xendev, &local_err);
You can't reuse local_err here, *local_err must be null (It isn't
exactly written like this, but that what I understand from reading
qapi/error.h).
Maybe you meant to return when the previous function failed (call of
xs_node_create)?
> + if (local_err) {
> + error_propagate(errp, local_err);
> + error_prepend(errp, "failed to watch frontend state: ");
> + }
> }
Thanks,
--
Anthony PERARD
- Re: [Qemu-block] [PATCH 05/18] xen: add xenstore watcher infratructure,
Anthony PERARD <=