hw/xen: Add xenstore wire implementation and implementation stubs

This implements the basic wire protocol for the XenStore commands, punting
all the actual implementation to xs_impl_* functions which all just return
errors for now.

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

hw/i386/kvm/meson.build

@@ -9,6 +9,7 @@ i386_kvm_ss.add(when: 'CONFIG_XEN_EMU', if_true: files(
   'xen_evtchn.c',
   'xen_gnttab.c',
   'xen_xenstore.c',
+  'xenstore_impl.c',
   ))
 
 i386_ss.add_all(when: 'CONFIG_KVM', if_true: i386_kvm_ss)

hw/i386/kvm/trace-events

@@ -3,3 +3,18 @@ kvm_xen_unmap_pirq(int pirq, int gsi) "pirq %d gsi %d"
 kvm_xen_get_free_pirq(int pirq, int type) "pirq %d type %d"
 kvm_xen_bind_pirq(int pirq, int port) "pirq %d port %d"
 kvm_xen_unmask_pirq(int pirq, char *dev, int vector) "pirq %d dev %s vector %d"
+xenstore_error(unsigned int id, unsigned int tx_id, const char *err) "req %u tx %u err %s"
+xenstore_read(unsigned int tx_id, const char *path) "tx %u path %s"
+xenstore_write(unsigned int tx_id, const char *path) "tx %u path %s"
+xenstore_mkdir(unsigned int tx_id, const char *path) "tx %u path %s"
+xenstore_directory(unsigned int tx_id, const char *path) "tx %u path %s"
+xenstore_directory_part(unsigned int tx_id, const char *path, unsigned int offset) "tx %u path %s offset %u"
+xenstore_transaction_start(unsigned int new_tx) "new_tx %u"
+xenstore_transaction_end(unsigned int tx_id, bool commit) "tx %u commit %d"
+xenstore_rm(unsigned int tx_id, const char *path) "tx %u path %s"
+xenstore_get_perms(unsigned int tx_id, const char *path) "tx %u path %s"
+xenstore_set_perms(unsigned int tx_id, const char *path) "tx %u path %s"
+xenstore_watch(const char *path, const char *token) "path %s token %s"
+xenstore_unwatch(const char *path, const char *token) "path %s token %s"
+xenstore_reset_watches(void) ""
+xenstore_watch_event(const char *path, const char *token) "path %s token %s"

hw/i386/kvm/xenstore_impl.c

@@ -0,0 +1,117 @@
+/*
+ * QEMU Xen emulation: The actual implementation of XenStore
+ *
+ * Copyright © 2023 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Authors: David Woodhouse <dwmw2@infradead.org>, Paul Durrant <paul@xen.org>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+
+#include "xen_xenstore.h"
+#include "xenstore_impl.h"
+
+struct XenstoreImplState {
+};
+
+int xs_impl_read(XenstoreImplState *s, unsigned int dom_id,
+                 xs_transaction_t tx_id, const char *path, GByteArray *data)
+{
+    /*
+     * The data GByteArray shall exist, and will be freed by caller.
+     * Just g_byte_array_append() to it.
+     */
+    return ENOENT;
+}
+
+int xs_impl_write(XenstoreImplState *s, unsigned int dom_id,
+                  xs_transaction_t tx_id, const char *path, GByteArray *data)
+{
+    /*
+     * The data GByteArray shall exist, will be freed by caller. You are
+     * free to use g_byte_array_steal() and keep the data.
+     */
+    return ENOSYS;
+}
+
+int xs_impl_directory(XenstoreImplState *s, unsigned int dom_id,
+                      xs_transaction_t tx_id, const char *path,
+                      uint64_t *gencnt, GList **items)
+{
+    /*
+     * The items are (char *) to be freed by caller. Although it's consumed
+     * immediately so if you want to change it to (const char *) and keep
+     * them, go ahead and change the caller.
+     */
+    return ENOENT;
+}
+
+int xs_impl_transaction_start(XenstoreImplState *s, unsigned int dom_id,
+                              xs_transaction_t *tx_id)
+{
+    return ENOSYS;
+}
+
+int xs_impl_transaction_end(XenstoreImplState *s, unsigned int dom_id,
+                            xs_transaction_t tx_id, bool commit)
+{
+    return ENOSYS;
+}
+
+int xs_impl_rm(XenstoreImplState *s, unsigned int dom_id,
+               xs_transaction_t tx_id, const char *path)
+{
+    return ENOSYS;
+}
+
+int xs_impl_get_perms(XenstoreImplState *s, unsigned int dom_id,
+                      xs_transaction_t tx_id, const char *path, GList **perms)
+{
+    /*
+     * The perms are (char *) in the <perm-as-string> wire format to be
+     * freed by the caller.
+     */
+    return ENOSYS;
+}
+
+int xs_impl_set_perms(XenstoreImplState *s, unsigned int dom_id,
+                      xs_transaction_t tx_id, const char *path, GList *perms)
+{
+    /*
+     * The perms are (const char *) in the <perm-as-string> wire format.
+     */
+    return ENOSYS;
+}
+
+int xs_impl_watch(XenstoreImplState *s, unsigned int dom_id, const char *path,
+                  const char *token, xs_impl_watch_fn fn, void *opaque)
+{
+    /*
+     * When calling the callback @fn, note that the path should
+     * precisely match the relative path that the guest provided, even
+     * if it was a relative path which needed to be prefixed with
+     * /local/domain/${domid}/
+     */
+    return ENOSYS;
+}
+
+int xs_impl_unwatch(XenstoreImplState *s, unsigned int dom_id,
+                    const char *path, const char *token,
+                    xs_impl_watch_fn fn, void *opaque)
+{
+    /* Remove the watch that matches all four criteria */
+    return ENOSYS;
+}
+
+int xs_impl_reset_watches(XenstoreImplState *s, unsigned int dom_id)
+{
+    return ENOSYS;
+}
+
+XenstoreImplState *xs_impl_create(void)
+{
+    return g_new0(XenstoreImplState, 1);
+}

hw/i386/kvm/xenstore_impl.h

@@ -0,0 +1,58 @@
+/*
+ * QEMU Xen emulation: The actual implementation of XenStore
+ *
+ * Copyright © 2023 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Authors: David Woodhouse <dwmw2@infradead.org>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#ifndef QEMU_XENSTORE_IMPL_H
+#define QEMU_XENSTORE_IMPL_H
+
+typedef uint32_t xs_transaction_t;
+
+#define XBT_NULL 0
+
+typedef struct XenstoreImplState XenstoreImplState;
+
+XenstoreImplState *xs_impl_create(void);
+
+/*
+ * These functions return *positive* error numbers. This is a little
+ * unconventional but it helps to keep us honest because there is
+ * also a very limited set of error numbers that they are permitted
+ * to return (those in xsd_errors).
+ */
+
+int xs_impl_read(XenstoreImplState *s, unsigned int dom_id,
+                 xs_transaction_t tx_id, const char *path, GByteArray *data);
+int xs_impl_write(XenstoreImplState *s, unsigned int dom_id,
+                  xs_transaction_t tx_id, const char *path, GByteArray *data);
+int xs_impl_directory(XenstoreImplState *s, unsigned int dom_id,
+                      xs_transaction_t tx_id, const char *path,
+                      uint64_t *gencnt, GList **items);
+int xs_impl_transaction_start(XenstoreImplState *s, unsigned int dom_id,
+                              xs_transaction_t *tx_id);
+int xs_impl_transaction_end(XenstoreImplState *s, unsigned int dom_id,
+                            xs_transaction_t tx_id, bool commit);
+int xs_impl_rm(XenstoreImplState *s, unsigned int dom_id,
+               xs_transaction_t tx_id, const char *path);
+int xs_impl_get_perms(XenstoreImplState *s, unsigned int dom_id,
+                      xs_transaction_t tx_id, const char *path, GList **perms);
+int xs_impl_set_perms(XenstoreImplState *s, unsigned int dom_id,
+                      xs_transaction_t tx_id, const char *path, GList *perms);
+
+/* This differs from xs_watch_fn because it has the token */
+typedef void(xs_impl_watch_fn)(void *opaque, const char *path,
+                               const char *token);
+int xs_impl_watch(XenstoreImplState *s, unsigned int dom_id, const char *path,
+                  const char *token, xs_impl_watch_fn fn, void *opaque);
+int xs_impl_unwatch(XenstoreImplState *s, unsigned int dom_id,
+                    const char *path, const char *token, xs_impl_watch_fn fn,
+                    void *opaque);
+int xs_impl_reset_watches(XenstoreImplState *s, unsigned int dom_id);
+
+#endif /* QEMU_XENSTORE_IMPL_H */