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qemu/hw/i386/kvm/xen_xenstore.c
David Woodhouse 766804b101 hw/xen: Implement core serialize/deserialize methods for xenstore_impl 
This implements the basic migration support in the back end, with unit
tests that give additional confidence in the node-counting already in
the tree.

However, the existing PV back ends like xen-disk don't support migration
yet. They will reset the ring and fail to continue where they left off.
We will fix that in future, but not in time for the 8.0 release.

Since there's also an open question of whether we want to serialize the
full XenStore or only the guest-owned nodes in /local/domain/${domid},
for now just mark the XenStore device as unmigratable.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
2023-03-07 17:04:30 +00:00

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/*
* QEMU Xen emulation: Shared/overlay pages support
*
* Copyright © 2022 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.
*/
#include "qemu/osdep.h"
#include "qemu/host-utils.h"
#include "qemu/module.h"
#include "qemu/main-loop.h"
#include "qemu/cutils.h"
#include "qapi/error.h"
#include "qom/object.h"
#include "migration/vmstate.h"
#include "hw/sysbus.h"
#include "hw/xen/xen.h"
#include "xen_overlay.h"
#include "xen_evtchn.h"
#include "xen_xenstore.h"
#include "sysemu/kvm.h"
#include "sysemu/kvm_xen.h"
#include "trace.h"
#include "xenstore_impl.h"
#include "hw/xen/interface/io/xs_wire.h"
#include "hw/xen/interface/event_channel.h"
#define TYPE_XEN_XENSTORE "xen-xenstore"
OBJECT_DECLARE_SIMPLE_TYPE(XenXenstoreState, XEN_XENSTORE)
#define XEN_PAGE_SHIFT 12
#define XEN_PAGE_SIZE (1ULL << XEN_PAGE_SHIFT)
#define ENTRIES_PER_FRAME_V1 (XEN_PAGE_SIZE / sizeof(grant_entry_v1_t))
#define ENTRIES_PER_FRAME_V2 (XEN_PAGE_SIZE / sizeof(grant_entry_v2_t))
#define XENSTORE_HEADER_SIZE ((unsigned int)sizeof(struct xsd_sockmsg))
struct XenXenstoreState {
/*< private >*/
SysBusDevice busdev;
/*< public >*/
XenstoreImplState *impl;
GList *watch_events;
MemoryRegion xenstore_page;
struct xenstore_domain_interface *xs;
uint8_t req_data[XENSTORE_HEADER_SIZE + XENSTORE_PAYLOAD_MAX];
uint8_t rsp_data[XENSTORE_HEADER_SIZE + XENSTORE_PAYLOAD_MAX];
uint32_t req_offset;
uint32_t rsp_offset;
bool rsp_pending;
bool fatal_error;
evtchn_port_t guest_port;
evtchn_port_t be_port;
struct xenevtchn_handle *eh;
uint8_t *impl_state;
uint32_t impl_state_size;
};
struct XenXenstoreState *xen_xenstore_singleton;
static void xen_xenstore_event(void *opaque);
static void fire_watch_cb(void *opaque, const char *path, const char *token);
static void xen_xenstore_realize(DeviceState *dev, Error **errp)
{
XenXenstoreState *s = XEN_XENSTORE(dev);
if (xen_mode != XEN_EMULATE) {
error_setg(errp, "Xen xenstore support is for Xen emulation");
return;
}
memory_region_init_ram(&s->xenstore_page, OBJECT(dev), "xen:xenstore_page",
XEN_PAGE_SIZE, &error_abort);
memory_region_set_enabled(&s->xenstore_page, true);
s->xs = memory_region_get_ram_ptr(&s->xenstore_page);
memset(s->xs, 0, XEN_PAGE_SIZE);
/* We can't map it this early as KVM isn't ready */
xen_xenstore_singleton = s;
s->eh = xen_be_evtchn_open();
if (!s->eh) {
error_setg(errp, "Xenstore evtchn port init failed");
return;
}
aio_set_fd_handler(qemu_get_aio_context(), xen_be_evtchn_fd(s->eh), true,
xen_xenstore_event, NULL, NULL, NULL, s);
s->impl = xs_impl_create(xen_domid);
}
static bool xen_xenstore_is_needed(void *opaque)
{
return xen_mode == XEN_EMULATE;
}
static int xen_xenstore_pre_save(void *opaque)
{
XenXenstoreState *s = opaque;
GByteArray *save;
if (s->eh) {
s->guest_port = xen_be_evtchn_get_guest_port(s->eh);
}
g_free(s->impl_state);
save = xs_impl_serialize(s->impl);
s->impl_state = save->data;
s->impl_state_size = save->len;
g_byte_array_free(save, false);
return 0;
}
static int xen_xenstore_post_load(void *opaque, int ver)
{
XenXenstoreState *s = opaque;
GByteArray *save;
int ret;
/*
* As qemu/dom0, rebind to the guest's port. The Windows drivers may
* unbind the XenStore evtchn and rebind to it, having obtained the
* "remote" port through EVTCHNOP_status. In the case that migration
* occurs while it's unbound, the "remote" port needs to be the same
* as before so that the guest can find it, but should remain unbound.
*/
if (s->guest_port) {
int be_port = xen_be_evtchn_bind_interdomain(s->eh, xen_domid,
s->guest_port);
if (be_port < 0) {
return be_port;
}
s->be_port = be_port;
}
save = g_byte_array_new_take(s->impl_state, s->impl_state_size);
s->impl_state = NULL;
s->impl_state_size = 0;
ret = xs_impl_deserialize(s->impl, save, xen_domid, fire_watch_cb, s);
return ret;
}
static const VMStateDescription xen_xenstore_vmstate = {
.name = "xen_xenstore",
.unmigratable = 1, /* The PV back ends don't migrate yet */
.version_id = 1,
.minimum_version_id = 1,
.needed = xen_xenstore_is_needed,
.pre_save = xen_xenstore_pre_save,
.post_load = xen_xenstore_post_load,
.fields = (VMStateField[]) {
VMSTATE_UINT8_ARRAY(req_data, XenXenstoreState,
sizeof_field(XenXenstoreState, req_data)),
VMSTATE_UINT8_ARRAY(rsp_data, XenXenstoreState,
sizeof_field(XenXenstoreState, rsp_data)),
VMSTATE_UINT32(req_offset, XenXenstoreState),
VMSTATE_UINT32(rsp_offset, XenXenstoreState),
VMSTATE_BOOL(rsp_pending, XenXenstoreState),
VMSTATE_UINT32(guest_port, XenXenstoreState),
VMSTATE_BOOL(fatal_error, XenXenstoreState),
VMSTATE_UINT32(impl_state_size, XenXenstoreState),
VMSTATE_VARRAY_UINT32_ALLOC(impl_state, XenXenstoreState,
impl_state_size, 0,
vmstate_info_uint8, uint8_t),
VMSTATE_END_OF_LIST()
}
};
static void xen_xenstore_class_init(ObjectClass *klass, void *data)
{
DeviceClass *dc = DEVICE_CLASS(klass);
dc->realize = xen_xenstore_realize;
dc->vmsd = &xen_xenstore_vmstate;
}
static const TypeInfo xen_xenstore_info = {
.name = TYPE_XEN_XENSTORE,
.parent = TYPE_SYS_BUS_DEVICE,
.instance_size = sizeof(XenXenstoreState),
.class_init = xen_xenstore_class_init,
};
void xen_xenstore_create(void)
{
DeviceState *dev = sysbus_create_simple(TYPE_XEN_XENSTORE, -1, NULL);
xen_xenstore_singleton = XEN_XENSTORE(dev);
/*
* Defer the init (xen_xenstore_reset()) until KVM is set up and the
* overlay page can be mapped.
*/
}
static void xen_xenstore_register_types(void)
{
type_register_static(&xen_xenstore_info);
}
type_init(xen_xenstore_register_types)
uint16_t xen_xenstore_get_port(void)
{
XenXenstoreState *s = xen_xenstore_singleton;
if (!s) {
return 0;
}
return s->guest_port;
}
static bool req_pending(XenXenstoreState *s)
{
struct xsd_sockmsg *req = (struct xsd_sockmsg *)s->req_data;
return s->req_offset == XENSTORE_HEADER_SIZE + req->len;
}
static void reset_req(XenXenstoreState *s)
{
memset(s->req_data, 0, sizeof(s->req_data));
s->req_offset = 0;
}
static void reset_rsp(XenXenstoreState *s)
{
s->rsp_pending = false;
memset(s->rsp_data, 0, sizeof(s->rsp_data));
s->rsp_offset = 0;
}
static void xs_error(XenXenstoreState *s, unsigned int id,
xs_transaction_t tx_id, int errnum)
{
struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
const char *errstr = NULL;
for (unsigned int i = 0; i < ARRAY_SIZE(xsd_errors); i++) {
struct xsd_errors *xsd_error = &xsd_errors[i];
if (xsd_error->errnum == errnum) {
errstr = xsd_error->errstring;
break;
}
}
assert(errstr);
trace_xenstore_error(id, tx_id, errstr);
rsp->type = XS_ERROR;
rsp->req_id = id;
rsp->tx_id = tx_id;
rsp->len = (uint32_t)strlen(errstr) + 1;
memcpy(&rsp[1], errstr, rsp->len);
}
static void xs_ok(XenXenstoreState *s, unsigned int type, unsigned int req_id,
xs_transaction_t tx_id)
{
struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
const char *okstr = "OK";
rsp->type = type;
rsp->req_id = req_id;
rsp->tx_id = tx_id;
rsp->len = (uint32_t)strlen(okstr) + 1;
memcpy(&rsp[1], okstr, rsp->len);
}
/*
* The correct request and response formats are documented in xen.git:
* docs/misc/xenstore.txt. A summary is given below for convenience.
* The '|' symbol represents a NUL character.
*
* ---------- Database read, write and permissions operations ----------
*
* READ <path>| <value|>
* WRITE <path>|<value|>
* Store and read the octet string <value> at <path>.
* WRITE creates any missing parent paths, with empty values.
*
* MKDIR <path>|
* Ensures that the <path> exists, by necessary by creating
* it and any missing parents with empty values. If <path>
* or any parent already exists, its value is left unchanged.
*
* RM <path>|
* Ensures that the <path> does not exist, by deleting
* it and all of its children. It is not an error if <path> does
* not exist, but it _is_ an error if <path>'s immediate parent
* does not exist either.
*
* DIRECTORY <path>| <child-leaf-name>|*
* Gives a list of the immediate children of <path>, as only the
* leafnames. The resulting children are each named
* <path>/<child-leaf-name>.
*
* DIRECTORY_PART <path>|<offset> <gencnt>|<child-leaf-name>|*
* Same as DIRECTORY, but to be used for children lists longer than
* XENSTORE_PAYLOAD_MAX. Input are <path> and the byte offset into
* the list of children to return. Return values are the generation
* count <gencnt> of the node (to be used to ensure the node hasn't
* changed between two reads: <gencnt> being the same for multiple
* reads guarantees the node hasn't changed) and the list of children
* starting at the specified <offset> of the complete list.
*
* GET_PERMS <path>| <perm-as-string>|+
* SET_PERMS <path>|<perm-as-string>|+?
* <perm-as-string> is one of the following
* w<domid> write only
* r<domid> read only
* b<domid> both read and write
* n<domid> no access
* See https://wiki.xen.org/wiki/XenBus section
* `Permissions' for details of the permissions system.
* It is possible to set permissions for the special watch paths
* "@introduceDomain" and "@releaseDomain" to enable receiving those
* watches in unprivileged domains.
*
* ---------- Watches ----------
*
* WATCH <wpath>|<token>|?
* Adds a watch.
*
* When a <path> is modified (including path creation, removal,
* contents change or permissions change) this generates an event
* on the changed <path>. Changes made in transactions cause an
* event only if and when committed. Each occurring event is
* matched against all the watches currently set up, and each
* matching watch results in a WATCH_EVENT message (see below).
*
* The event's path matches the watch's <wpath> if it is an child
* of <wpath>.
*
* <wpath> can be a <path> to watch or @<wspecial>. In the
* latter case <wspecial> may have any syntax but it matches
* (according to the rules above) only the following special
* events which are invented by xenstored:
* @introduceDomain occurs on INTRODUCE
* @releaseDomain occurs on any domain crash or
* shutdown, and also on RELEASE
* and domain destruction
* <wspecial> events are sent to privileged callers or explicitly
* via SET_PERMS enabled domains only.
*
* When a watch is first set up it is triggered once straight
* away, with <path> equal to <wpath>. Watches may be triggered
* spuriously. The tx_id in a WATCH request is ignored.
*
* Watches are supposed to be restricted by the permissions
* system but in practice the implementation is imperfect.
* Applications should not rely on being sent a notification for
* paths that they cannot read; however, an application may rely
* on being sent a watch when a path which it _is_ able to read
* is deleted even if that leaves only a nonexistent unreadable
* parent. A notification may omitted if a node's permissions
* are changed so as to make it unreadable, in which case future
* notifications may be suppressed (and if the node is later made
* readable, some notifications may have been lost).
*
* WATCH_EVENT <epath>|<token>|
* Unsolicited `reply' generated for matching modification events
* as described above. req_id and tx_id are both 0.
*
* <epath> is the event's path, ie the actual path that was
* modified; however if the event was the recursive removal of an
* parent of <wpath>, <epath> is just
* <wpath> (rather than the actual path which was removed). So
* <epath> is a child of <wpath>, regardless.
*
* Iff <wpath> for the watch was specified as a relative pathname,
* the <epath> path will also be relative (with the same base,
* obviously).
*
* UNWATCH <wpath>|<token>|?
*
* RESET_WATCHES |
* Reset all watches and transactions of the caller.
*
* ---------- Transactions ----------
*
* TRANSACTION_START | <transid>|
* <transid> is an opaque uint32_t allocated by xenstored
* represented as unsigned decimal. After this, transaction may
* be referenced by using <transid> (as 32-bit binary) in the
* tx_id request header field. When transaction is started whole
* db is copied; reads and writes happen on the copy.
* It is not legal to send non-0 tx_id in TRANSACTION_START.
*
* TRANSACTION_END T|
* TRANSACTION_END F|
* tx_id must refer to existing transaction. After this
* request the tx_id is no longer valid and may be reused by
* xenstore. If F, the transaction is discarded. If T,
* it is committed: if there were any other intervening writes
* then our END gets get EAGAIN.
*
* The plan is that in the future only intervening `conflicting'
* writes cause EAGAIN, meaning only writes or other commits
* which changed paths which were read or written in the
* transaction at hand.
*
*/
static void xs_read(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data, unsigned int len)
{
const char *path = (const char *)req_data;
struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
uint8_t *rsp_data = (uint8_t *)&rsp[1];
g_autoptr(GByteArray) data = g_byte_array_new();
int err;
if (len == 0 || req_data[len - 1] != '\0') {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
trace_xenstore_read(tx_id, path);
err = xs_impl_read(s->impl, xen_domid, tx_id, path, data);
if (err) {
xs_error(s, req_id, tx_id, err);
return;
}
rsp->type = XS_READ;
rsp->req_id = req_id;
rsp->tx_id = tx_id;
rsp->len = 0;
len = data->len;
if (len > XENSTORE_PAYLOAD_MAX) {
xs_error(s, req_id, tx_id, E2BIG);
return;
}
memcpy(&rsp_data[rsp->len], data->data, len);
rsp->len += len;
}
static void xs_write(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
g_autoptr(GByteArray) data = g_byte_array_new();
const char *path;
int err;
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
path = (const char *)req_data;
while (len--) {
if (*req_data++ == '\0') {
break;
}
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
}
g_byte_array_append(data, req_data, len);
trace_xenstore_write(tx_id, path);
err = xs_impl_write(s->impl, xen_domid, tx_id, path, data);
if (err) {
xs_error(s, req_id, tx_id, err);
return;
}
xs_ok(s, XS_WRITE, req_id, tx_id);
}
static void xs_mkdir(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
g_autoptr(GByteArray) data = g_byte_array_new();
const char *path;
int err;
if (len == 0 || req_data[len - 1] != '\0') {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
path = (const char *)req_data;
trace_xenstore_mkdir(tx_id, path);
err = xs_impl_read(s->impl, xen_domid, tx_id, path, data);
if (err == ENOENT) {
err = xs_impl_write(s->impl, xen_domid, tx_id, path, data);
}
if (!err) {
xs_error(s, req_id, tx_id, err);
return;
}
xs_ok(s, XS_MKDIR, req_id, tx_id);
}
static void xs_append_strings(XenXenstoreState *s, struct xsd_sockmsg *rsp,
GList *strings, unsigned int start, bool truncate)
{
uint8_t *rsp_data = (uint8_t *)&rsp[1];
GList *l;
for (l = strings; l; l = l->next) {
size_t len = strlen(l->data) + 1; /* Including the NUL termination */
char *str = l->data;
if (rsp->len + len > XENSTORE_PAYLOAD_MAX) {
if (truncate) {
len = XENSTORE_PAYLOAD_MAX - rsp->len;
if (!len) {
return;
}
} else {
xs_error(s, rsp->req_id, rsp->tx_id, E2BIG);
return;
}
}
if (start) {
if (start >= len) {
start -= len;
continue;
}
str += start;
len -= start;
start = 0;
}
memcpy(&rsp_data[rsp->len], str, len);
rsp->len += len;
}
/* XS_DIRECTORY_PART wants an extra NUL to indicate the end */
if (truncate && rsp->len < XENSTORE_PAYLOAD_MAX) {
rsp_data[rsp->len++] = '\0';
}
}
static void xs_directory(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
GList *items = NULL;
const char *path;
int err;
if (len == 0 || req_data[len - 1] != '\0') {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
path = (const char *)req_data;
trace_xenstore_directory(tx_id, path);
err = xs_impl_directory(s->impl, xen_domid, tx_id, path, NULL, &items);
if (err != 0) {
xs_error(s, req_id, tx_id, err);
return;
}
rsp->type = XS_DIRECTORY;
rsp->req_id = req_id;
rsp->tx_id = tx_id;
rsp->len = 0;
xs_append_strings(s, rsp, items, 0, false);
g_list_free_full(items, g_free);
}
static void xs_directory_part(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
const char *offset_str, *path = (const char *)req_data;
struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
char *rsp_data = (char *)&rsp[1];
uint64_t gencnt = 0;
unsigned int offset;
GList *items = NULL;
int err;
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
while (len--) {
if (*req_data++ == '\0') {
break;
}
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
}
offset_str = (const char *)req_data;
while (len--) {
if (*req_data++ == '\0') {
break;
}
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
}
if (len) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
if (qemu_strtoui(offset_str, NULL, 10, &offset) < 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
trace_xenstore_directory_part(tx_id, path, offset);
err = xs_impl_directory(s->impl, xen_domid, tx_id, path, &gencnt, &items);
if (err != 0) {
xs_error(s, req_id, tx_id, err);
return;
}
rsp->type = XS_DIRECTORY_PART;
rsp->req_id = req_id;
rsp->tx_id = tx_id;
rsp->len = snprintf(rsp_data, XENSTORE_PAYLOAD_MAX, "%" PRIu64, gencnt) + 1;
xs_append_strings(s, rsp, items, offset, true);
g_list_free_full(items, g_free);
}
static void xs_transaction_start(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
char *rsp_data = (char *)&rsp[1];
int err;
if (len != 1 || req_data[0] != '\0') {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
rsp->type = XS_TRANSACTION_START;
rsp->req_id = req_id;
rsp->tx_id = tx_id;
rsp->len = 0;
err = xs_impl_transaction_start(s->impl, xen_domid, &tx_id);
if (err) {
xs_error(s, req_id, tx_id, err);
return;
}
trace_xenstore_transaction_start(tx_id);
rsp->len = snprintf(rsp_data, XENSTORE_PAYLOAD_MAX, "%u", tx_id);
assert(rsp->len < XENSTORE_PAYLOAD_MAX);
rsp->len++;
}
static void xs_transaction_end(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
bool commit;
int err;
if (len != 2 || req_data[1] != '\0') {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
switch (req_data[0]) {
case 'T':
commit = true;
break;
case 'F':
commit = false;
break;
default:
xs_error(s, req_id, tx_id, EINVAL);
return;
}
trace_xenstore_transaction_end(tx_id, commit);
err = xs_impl_transaction_end(s->impl, xen_domid, tx_id, commit);
if (err) {
xs_error(s, req_id, tx_id, err);
return;
}
xs_ok(s, XS_TRANSACTION_END, req_id, tx_id);
}
static void xs_rm(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data, unsigned int len)
{
const char *path = (const char *)req_data;
int err;
if (len == 0 || req_data[len - 1] != '\0') {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
trace_xenstore_rm(tx_id, path);
err = xs_impl_rm(s->impl, xen_domid, tx_id, path);
if (err) {
xs_error(s, req_id, tx_id, err);
return;
}
xs_ok(s, XS_RM, req_id, tx_id);
}
static void xs_get_perms(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
const char *path = (const char *)req_data;
struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
GList *perms = NULL;
int err;
if (len == 0 || req_data[len - 1] != '\0') {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
trace_xenstore_get_perms(tx_id, path);
err = xs_impl_get_perms(s->impl, xen_domid, tx_id, path, &perms);
if (err) {
xs_error(s, req_id, tx_id, err);
return;
}
rsp->type = XS_GET_PERMS;
rsp->req_id = req_id;
rsp->tx_id = tx_id;
rsp->len = 0;
xs_append_strings(s, rsp, perms, 0, false);
g_list_free_full(perms, g_free);
}
static void xs_set_perms(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
const char *path = (const char *)req_data;
uint8_t *perm;
GList *perms = NULL;
int err;
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
while (len--) {
if (*req_data++ == '\0') {
break;
}
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
}
perm = req_data;
while (len--) {
if (*req_data++ == '\0') {
perms = g_list_append(perms, perm);
perm = req_data;
}
}
/*
* Note that there may be trailing garbage at the end of the buffer.
* This is explicitly permitted by the '?' at the end of the definition:
*
* SET_PERMS <path>|<perm-as-string>|+?
*/
trace_xenstore_set_perms(tx_id, path);
err = xs_impl_set_perms(s->impl, xen_domid, tx_id, path, perms);
g_list_free(perms);
if (err) {
xs_error(s, req_id, tx_id, err);
return;
}
xs_ok(s, XS_SET_PERMS, req_id, tx_id);
}
static void xs_watch(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
const char *token, *path = (const char *)req_data;
int err;
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
while (len--) {
if (*req_data++ == '\0') {
break;
}
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
}
token = (const char *)req_data;
while (len--) {
if (*req_data++ == '\0') {
break;
}
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
}
/*
* Note that there may be trailing garbage at the end of the buffer.
* This is explicitly permitted by the '?' at the end of the definition:
*
* WATCH <wpath>|<token>|?
*/
trace_xenstore_watch(path, token);
err = xs_impl_watch(s->impl, xen_domid, path, token, fire_watch_cb, s);
if (err) {
xs_error(s, req_id, tx_id, err);
return;
}
xs_ok(s, XS_WATCH, req_id, tx_id);
}
static void xs_unwatch(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
const char *token, *path = (const char *)req_data;
int err;
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
while (len--) {
if (*req_data++ == '\0') {
break;
}
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
}
token = (const char *)req_data;
while (len--) {
if (*req_data++ == '\0') {
break;
}
if (len == 0) {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
}
trace_xenstore_unwatch(path, token);
err = xs_impl_unwatch(s->impl, xen_domid, path, token, fire_watch_cb, s);
if (err) {
xs_error(s, req_id, tx_id, err);
return;
}
xs_ok(s, XS_UNWATCH, req_id, tx_id);
}
static void xs_reset_watches(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *req_data,
unsigned int len)
{
if (len == 0 || req_data[len - 1] != '\0') {
xs_error(s, req_id, tx_id, EINVAL);
return;
}
trace_xenstore_reset_watches();
xs_impl_reset_watches(s->impl, xen_domid);
xs_ok(s, XS_RESET_WATCHES, req_id, tx_id);
}
static void xs_priv(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *data,
unsigned int len)
{
xs_error(s, req_id, tx_id, EACCES);
}
static void xs_unimpl(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *data,
unsigned int len)
{
xs_error(s, req_id, tx_id, ENOSYS);
}
typedef void (*xs_impl)(XenXenstoreState *s, unsigned int req_id,
xs_transaction_t tx_id, uint8_t *data,
unsigned int len);
struct xsd_req {
const char *name;
xs_impl fn;
};
#define XSD_REQ(_type, _fn) \
[_type] = { .name = #_type, .fn = _fn }
struct xsd_req xsd_reqs[] = {
XSD_REQ(XS_READ, xs_read),
XSD_REQ(XS_WRITE, xs_write),
XSD_REQ(XS_MKDIR, xs_mkdir),
XSD_REQ(XS_DIRECTORY, xs_directory),
XSD_REQ(XS_DIRECTORY_PART, xs_directory_part),
XSD_REQ(XS_TRANSACTION_START, xs_transaction_start),
XSD_REQ(XS_TRANSACTION_END, xs_transaction_end),
XSD_REQ(XS_RM, xs_rm),
XSD_REQ(XS_GET_PERMS, xs_get_perms),
XSD_REQ(XS_SET_PERMS, xs_set_perms),
XSD_REQ(XS_WATCH, xs_watch),
XSD_REQ(XS_UNWATCH, xs_unwatch),
XSD_REQ(XS_CONTROL, xs_priv),
XSD_REQ(XS_INTRODUCE, xs_priv),
XSD_REQ(XS_RELEASE, xs_priv),
XSD_REQ(XS_IS_DOMAIN_INTRODUCED, xs_priv),
XSD_REQ(XS_RESUME, xs_priv),
XSD_REQ(XS_SET_TARGET, xs_priv),
XSD_REQ(XS_RESET_WATCHES, xs_reset_watches),
};
static void process_req(XenXenstoreState *s)
{
struct xsd_sockmsg *req = (struct xsd_sockmsg *)s->req_data;
xs_impl handler = NULL;
assert(req_pending(s));
assert(!s->rsp_pending);
if (req->type < ARRAY_SIZE(xsd_reqs)) {
handler = xsd_reqs[req->type].fn;
}
if (!handler) {
handler = &xs_unimpl;
}
handler(s, req->req_id, req->tx_id, (uint8_t *)&req[1], req->len);
s->rsp_pending = true;
reset_req(s);
}
static unsigned int copy_from_ring(XenXenstoreState *s, uint8_t *ptr,
unsigned int len)
{
if (!len) {
return 0;
}
XENSTORE_RING_IDX prod = qatomic_read(&s->xs->req_prod);
XENSTORE_RING_IDX cons = qatomic_read(&s->xs->req_cons);
unsigned int copied = 0;
/* Ensure the ring contents don't cross the req_prod access. */
smp_rmb();
while (len) {
unsigned int avail = prod - cons;
unsigned int offset = MASK_XENSTORE_IDX(cons);
unsigned int copylen = avail;
if (avail > XENSTORE_RING_SIZE) {
error_report("XenStore ring handling error");
s->fatal_error = true;
break;
} else if (avail == 0) {
break;
}
if (copylen > len) {
copylen = len;
}
if (copylen > XENSTORE_RING_SIZE - offset) {
copylen = XENSTORE_RING_SIZE - offset;
}
memcpy(ptr, &s->xs->req[offset], copylen);
copied += copylen;
ptr += copylen;
len -= copylen;
cons += copylen;
}
/*
* Not sure this ever mattered except on Alpha, but this barrier
* is to ensure that the update to req_cons is globally visible
* only after we have consumed all the data from the ring, and we
* don't end up seeing data written to the ring *after* the other
* end sees the update and writes more to the ring. Xen's own
* xenstored has the same barrier here (although with no comment
* at all, obviously, because it's Xen code).
*/
smp_mb();
qatomic_set(&s->xs->req_cons, cons);
return copied;
}
static unsigned int copy_to_ring(XenXenstoreState *s, uint8_t *ptr,
unsigned int len)
{
if (!len) {
return 0;
}
XENSTORE_RING_IDX cons = qatomic_read(&s->xs->rsp_cons);
XENSTORE_RING_IDX prod = qatomic_read(&s->xs->rsp_prod);
unsigned int copied = 0;
/*
* This matches the barrier in copy_to_ring() (or the guest's
* equivalent) betweem writing the data to the ring and updating
* rsp_prod. It protects against the pathological case (which
* again I think never happened except on Alpha) where our
* subsequent writes to the ring could *cross* the read of
* rsp_cons and the guest could see the new data when it was
* intending to read the old.
*/
smp_mb();
while (len) {
unsigned int avail = cons + XENSTORE_RING_SIZE - prod;
unsigned int offset = MASK_XENSTORE_IDX(prod);
unsigned int copylen = len;
if (avail > XENSTORE_RING_SIZE) {
error_report("XenStore ring handling error");
s->fatal_error = true;
break;
} else if (avail == 0) {
break;
}
if (copylen > avail) {
copylen = avail;
}
if (copylen > XENSTORE_RING_SIZE - offset) {
copylen = XENSTORE_RING_SIZE - offset;
}
memcpy(&s->xs->rsp[offset], ptr, copylen);
copied += copylen;
ptr += copylen;
len -= copylen;
prod += copylen;
}
/* Ensure the ring contents are seen before rsp_prod update. */
smp_wmb();
qatomic_set(&s->xs->rsp_prod, prod);
return copied;
}
static unsigned int get_req(XenXenstoreState *s)
{
unsigned int copied = 0;
if (s->fatal_error) {
return 0;
}
assert(!req_pending(s));
if (s->req_offset < XENSTORE_HEADER_SIZE) {
void *ptr = s->req_data + s->req_offset;
unsigned int len = XENSTORE_HEADER_SIZE;
unsigned int copylen = copy_from_ring(s, ptr, len);
copied += copylen;
s->req_offset += copylen;
}
if (s->req_offset >= XENSTORE_HEADER_SIZE) {
struct xsd_sockmsg *req = (struct xsd_sockmsg *)s->req_data;
if (req->len > (uint32_t)XENSTORE_PAYLOAD_MAX) {
error_report("Illegal XenStore request");
s->fatal_error = true;
return 0;
}
void *ptr = s->req_data + s->req_offset;
unsigned int len = XENSTORE_HEADER_SIZE + req->len - s->req_offset;
unsigned int copylen = copy_from_ring(s, ptr, len);
copied += copylen;
s->req_offset += copylen;
}
return copied;
}
static unsigned int put_rsp(XenXenstoreState *s)
{
if (s->fatal_error) {
return 0;
}
assert(s->rsp_pending);
struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
assert(s->rsp_offset < XENSTORE_HEADER_SIZE + rsp->len);
void *ptr = s->rsp_data + s->rsp_offset;
unsigned int len = XENSTORE_HEADER_SIZE + rsp->len - s->rsp_offset;
unsigned int copylen = copy_to_ring(s, ptr, len);
s->rsp_offset += copylen;
/* Have we produced a complete response? */
if (s->rsp_offset == XENSTORE_HEADER_SIZE + rsp->len) {
reset_rsp(s);
}
return copylen;
}
static void deliver_watch(XenXenstoreState *s, const char *path,
const char *token)
{
struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
uint8_t *rsp_data = (uint8_t *)&rsp[1];
unsigned int len;
assert(!s->rsp_pending);
trace_xenstore_watch_event(path, token);
rsp->type = XS_WATCH_EVENT;
rsp->req_id = 0;
rsp->tx_id = 0;
rsp->len = 0;
len = strlen(path);
/* XENSTORE_ABS/REL_PATH_MAX should ensure there can be no overflow */
assert(rsp->len + len < XENSTORE_PAYLOAD_MAX);
memcpy(&rsp_data[rsp->len], path, len);
rsp->len += len;
rsp_data[rsp->len] = '\0';
rsp->len++;
len = strlen(token);
/*
* It is possible for the guest to have chosen a token that will
* not fit (along with the patch) into a watch event. We have no
* choice but to drop the event if this is the case.
*/
if (rsp->len + len >= XENSTORE_PAYLOAD_MAX) {
return;
}
memcpy(&rsp_data[rsp->len], token, len);
rsp->len += len;
rsp_data[rsp->len] = '\0';
rsp->len++;
s->rsp_pending = true;
}
struct watch_event {
char *path;
char *token;
};
static void queue_watch(XenXenstoreState *s, const char *path,
const char *token)
{
struct watch_event *ev = g_new0(struct watch_event, 1);
ev->path = g_strdup(path);
ev->token = g_strdup(token);
s->watch_events = g_list_append(s->watch_events, ev);
}
static void fire_watch_cb(void *opaque, const char *path, const char *token)
{
XenXenstoreState *s = opaque;
assert(qemu_mutex_iothread_locked());
/*
* If there's a response pending, we obviously can't scribble over
* it. But if there's a request pending, it has dibs on the buffer
* too.
*
* In the common case of a watch firing due to backend activity
* when the ring was otherwise idle, we should be able to copy the
* strings directly into the rsp_data and thence the actual ring,
* without needing to perform any allocations and queue them.
*/
if (s->rsp_pending || req_pending(s)) {
queue_watch(s, path, token);
} else {
deliver_watch(s, path, token);
/*
* If the message was queued because there was already ring activity,
* no need to wake the guest. But if not, we need to send the evtchn.
*/
xen_be_evtchn_notify(s->eh, s->be_port);
}
}
static void process_watch_events(XenXenstoreState *s)
{
struct watch_event *ev = s->watch_events->data;
deliver_watch(s, ev->path, ev->token);
s->watch_events = g_list_remove(s->watch_events, ev);
g_free(ev->path);
g_free(ev->token);
g_free(ev);
}
static void xen_xenstore_event(void *opaque)
{
XenXenstoreState *s = opaque;
evtchn_port_t port = xen_be_evtchn_pending(s->eh);
unsigned int copied_to, copied_from;
bool processed, notify = false;
if (port != s->be_port) {
return;
}
/* We know this is a no-op. */
xen_be_evtchn_unmask(s->eh, port);
do {
copied_to = copied_from = 0;
processed = false;
if (!s->rsp_pending && s->watch_events) {
process_watch_events(s);
}
if (s->rsp_pending) {
copied_to = put_rsp(s);
}
if (!req_pending(s)) {
copied_from = get_req(s);
}
if (req_pending(s) && !s->rsp_pending && !s->watch_events) {
process_req(s);
processed = true;
}
notify |= copied_to || copied_from;
} while (copied_to || copied_from || processed);
if (notify) {
xen_be_evtchn_notify(s->eh, s->be_port);
}
}
static void alloc_guest_port(XenXenstoreState *s)
{
struct evtchn_alloc_unbound alloc = {
.dom = DOMID_SELF,
.remote_dom = DOMID_QEMU,
};
if (!xen_evtchn_alloc_unbound_op(&alloc)) {
s->guest_port = alloc.port;
}
}
int xen_xenstore_reset(void)
{
XenXenstoreState *s = xen_xenstore_singleton;
int err;
if (!s) {
return -ENOTSUP;
}
s->req_offset = s->rsp_offset = 0;
s->rsp_pending = false;
if (!memory_region_is_mapped(&s->xenstore_page)) {
uint64_t gpa = XEN_SPECIAL_PFN(XENSTORE) << TARGET_PAGE_BITS;
xen_overlay_do_map_page(&s->xenstore_page, gpa);
}
alloc_guest_port(s);
/*
* As qemu/dom0, bind to the guest's port. For incoming migration, this
* will be unbound as the guest's evtchn table is overwritten. We then
* rebind to the correct guest port in xen_xenstore_post_load().
*/
err = xen_be_evtchn_bind_interdomain(s->eh, xen_domid, s->guest_port);
if (err < 0) {
return err;
}
s->be_port = err;
return 0;
}
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