path: root/tools/xenstore/xenstored_control.c

/*
    Interactive commands for Xen Store Daemon.
    Copyright (C) 2017 Juergen Gross, SUSE Linux GmbH

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; If not, see <http://www.gnu.org/licenses/>.
*/

#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <xenctrl.h>

#include "utils.h"
#include "talloc.h"
#include "xs_lib.h"
#include "xenstored_core.h"
#include "xenstored_control.h"
#include "xenstored_domain.h"
#include "xenstored_watch.h"

/* Mini-OS only knows about MAP_ANON. */
#ifndef MAP_ANONYMOUS
#define MAP_ANONYMOUS MAP_ANON
#endif

#ifndef NO_LIVE_UPDATE
struct live_update {
	/* For verification the correct connection is acting. */
	struct connection *conn;

	/* Pointer to the command used to request LU */
	struct buffered_data *in;

#ifdef __MINIOS__
	void *kernel;
	unsigned int kernel_size;
	unsigned int kernel_off;

	void *dump_state;
	unsigned long dump_size;
#else
	char *filename;
#endif

	char *cmdline;

	/* Start parameters. */
	bool force;
	unsigned int timeout;
	time_t started_at;
};

static struct live_update *lu_status;

struct lu_dump_state {
	void *buf;
	unsigned int size;
#ifndef __MINIOS__
	int fd;
	char *filename;
#endif
};

static int lu_destroy(void *data)
{
#ifdef __MINIOS__
	if (lu_status->dump_state)
		munmap(lu_status->dump_state, lu_status->dump_size);
#endif
	lu_status = NULL;

	return 0;
}

static const char *lu_begin(struct connection *conn)
{
	if (lu_status)
		return "live-update session already active.";

	lu_status = talloc_zero(conn, struct live_update);
	if (!lu_status)
		return "Allocation failure.";
	lu_status->conn = conn;
	talloc_set_destructor(lu_status, lu_destroy);

	return NULL;
}

struct connection *lu_get_connection(void)
{
	return lu_status ? lu_status->conn : NULL;
}

unsigned int lu_write_response(FILE *fp)
{
	struct xsd_sockmsg msg;

	assert(lu_status);

	msg = lu_status->in->hdr.msg;

	msg.len = sizeof("OK");
	if (fp && fwrite(&msg, sizeof(msg), 1, fp) != 1)
		return 0;
	if (fp && fwrite("OK", msg.len, 1, fp) != 1)
		return 0;

	return sizeof(msg) + msg.len;
}

bool lu_is_pending(void)
{
	return lu_status != NULL;
}

#else
struct connection *lu_get_connection(void)
{
	return NULL;
}

unsigned int lu_write_response(FILE *fp)
{
	/* Unsupported */
	return 0;
}

bool lu_is_pending(void)
{
	return false;
}
#endif

struct cmd_s {
	char *cmd;
	int (*func)(const void *, struct connection *, char **, int);
	char *pars;
	/*
	 * max_pars can be used to limit the size of the parameter vector,
	 * e.g. in case of large binary parts in the parameters.
	 * The command is included in the count, so 1 means just the command
	 * without any parameter.
	 * 0 == no limit (the default)
	 */
	unsigned int max_pars;
};

static int do_control_check(const void *ctx, struct connection *conn,
			    char **vec, int num)
{
	if (num)
		return EINVAL;

	check_store();

	send_ack(conn, XS_CONTROL);
	return 0;
}

static int do_control_log(const void *ctx, struct connection *conn,
			  char **vec, int num)
{
	int ret;

	if (num == 0) {
		char *resp = talloc_asprintf(ctx, "Log switch settings:\n");
		unsigned int idx;
		bool on;

		if (!resp)
			return ENOMEM;
		for (idx = 0; trace_switches[idx]; idx++) {
			on = trace_flags & (1u << idx);
			resp = talloc_asprintf_append(resp, "%-8s: %s\n",
						      trace_switches[idx],
						      on ? "on" : "off");
			if (!resp)
				return ENOMEM;
		}

		send_reply(conn, XS_CONTROL, resp, strlen(resp) + 1);
		return 0;
	}

	if (num != 1)
		return EINVAL;

	if (!strcmp(vec[0], "on"))
		reopen_log();
	else if (!strcmp(vec[0], "off"))
		close_log();
	else {
		ret = set_trace_switch(vec[0]);
		if (ret)
			return ret;
	}

	send_ack(conn, XS_CONTROL);
	return 0;
}

struct quota {
	const char *name;
	int *quota;
	const char *descr;
};

static const struct quota hard_quotas[] = {
	{ "nodes", &quota_nb_entry_per_domain, "Nodes per domain" },
	{ "watches", &quota_nb_watch_per_domain, "Watches per domain" },
	{ "transactions", &quota_max_transaction, "Transactions per domain" },
	{ "outstanding", &quota_req_outstanding,
		"Outstanding requests per domain" },
	{ "transaction-nodes", &quota_trans_nodes,
		"Max. number of accessed nodes per transaction" },
	{ "memory", &quota_memory_per_domain_hard,
		"Total Xenstore memory per domain (error level)" },
	{ "node-size", &quota_max_entry_size, "Max. size of a node" },
	{ "path-max", &quota_max_path_len, "Max. length of a node path" },
	{ "permissions", &quota_nb_perms_per_node,
		"Max. number of permissions per node" },
	{ NULL, NULL, NULL }
};

static const struct quota soft_quotas[] = {
	{ "memory", &quota_memory_per_domain_soft,
		"Total Xenstore memory per domain (warning level)" },
	{ NULL, NULL, NULL }
};

static int quota_show_current(const void *ctx, struct connection *conn,
			      const struct quota *quotas)
{
	char *resp;
	unsigned int i;

	resp = talloc_strdup(ctx, "Quota settings:\n");
	if (!resp)
		return ENOMEM;

	for (i = 0; quotas[i].quota; i++) {
		resp = talloc_asprintf_append(resp, "%-17s: %8d %s\n",
					      quotas[i].name, *quotas[i].quota,
					      quotas[i].descr);
		if (!resp)
			return ENOMEM;
	}

	send_reply(conn, XS_CONTROL, resp, strlen(resp) + 1);

	return 0;
}

static int quota_set(const void *ctx, struct connection *conn,
		     char **vec, int num, const struct quota *quotas)
{
	unsigned int i;
	int val;

	if (num != 2)
		return EINVAL;

	val = atoi(vec[1]);
	if (val < 1)
		return EINVAL;

	for (i = 0; quotas[i].quota; i++) {
		if (!strcmp(vec[0], quotas[i].name)) {
			*quotas[i].quota = val;
			send_ack(conn, XS_CONTROL);
			return 0;
		}
	}

	return EINVAL;
}

static int quota_get(const void *ctx, struct connection *conn,
		     char **vec, int num)
{
	if (num != 1)
		return EINVAL;

	return domain_get_quota(ctx, conn, atoi(vec[0]));
}

static int do_control_quota(const void *ctx, struct connection *conn,
			    char **vec, int num)
{
	if (num == 0)
		return quota_show_current(ctx, conn, hard_quotas);

	if (!strcmp(vec[0], "set"))
		return quota_set(ctx, conn, vec + 1, num - 1, hard_quotas);

	return quota_get(ctx, conn, vec, num);
}

static int do_control_quota_s(const void *ctx, struct connection *conn,
			      char **vec, int num)
{
	if (num == 0)
		return quota_show_current(ctx, conn, soft_quotas);

	if (!strcmp(vec[0], "set"))
		return quota_set(ctx, conn, vec + 1, num - 1, soft_quotas);

	return EINVAL;
}

#ifdef __MINIOS__
static int do_control_memreport(const void *ctx, struct connection *conn,
				char **vec, int num)
{
	if (num)
		return EINVAL;

	talloc_report_full(NULL, stdout);

	send_ack(conn, XS_CONTROL);
	return 0;
}
#else
static int do_control_logfile(const void *ctx, struct connection *conn,
			      char **vec, int num)
{
	if (num != 1)
		return EINVAL;

	close_log();
	talloc_free(tracefile);
	tracefile = talloc_strdup(NULL, vec[0]);
	reopen_log();

	send_ack(conn, XS_CONTROL);
	return 0;
}

static int do_control_memreport(const void *ctx, struct connection *conn,
				char **vec, int num)
{
	FILE *fp;
	int fd;

	if (num > 1)
		return EINVAL;

	if (num == 0) {
		if (tracefd < 0) {
			if (!tracefile)
				return EBADF;
			fp = fopen(tracefile, "a");
		} else {
			/*
			 * Use dup() in order to avoid closing the file later
			 * with fclose() which will release stream resources.
			 */
			fd = dup(tracefd);
			if (fd < 0)
				return EBADF;
			fp = fdopen(fd, "a");
			if (!fp)
				close(fd);
		}
	} else
		fp = fopen(vec[0], "a");

	if (!fp)
		return EBADF;

	talloc_report_full(NULL, fp);
	fclose(fp);

	send_ack(conn, XS_CONTROL);
	return 0;
}
#endif

static int do_control_print(const void *ctx, struct connection *conn,
			    char **vec, int num)
{
	if (num != 1)
		return EINVAL;

	xprintf("control: %s", vec[0]);

	send_ack(conn, XS_CONTROL);
	return 0;
}

#ifndef NO_LIVE_UPDATE
static const char *lu_abort(const void *ctx, struct connection *conn)
{
	syslog(LOG_INFO, "live-update: abort\n");

	if (!lu_status)
		return "No live-update session active.";

	/* Destructor will do the real abort handling. */
	talloc_free(lu_status);

	return NULL;
}

static const char *lu_cmdline(const void *ctx, struct connection *conn,
			      const char *cmdline)
{
	syslog(LOG_INFO, "live-update: cmdline %s\n", cmdline);

	if (!lu_status || lu_status->conn != conn)
		return "Not in live-update session.";

	lu_status->cmdline = talloc_strdup(lu_status, cmdline);
	if (!lu_status->cmdline)
		return "Allocation failure.";

	return NULL;
}

#ifdef __MINIOS__
static const char *lu_binary_alloc(const void *ctx, struct connection *conn,
				   unsigned long size)
{
	const char *ret;

	syslog(LOG_INFO, "live-update: binary size %lu\n", size);

	ret = lu_begin(conn);
	if (ret)
		return ret;

	lu_status->kernel = talloc_size(lu_status, size);
	if (!lu_status->kernel)
		return "Allocation failure.";

	lu_status->kernel_size = size;
	lu_status->kernel_off = 0;

	errno = 0;
	return NULL;
}

static const char *lu_binary_save(const void *ctx, struct connection *conn,
				  unsigned int size, const char *data)
{
	if (!lu_status || lu_status->conn != conn)
		return "Not in live-update session.";

	if (lu_status->kernel_off + size > lu_status->kernel_size)
		return "Too much kernel data.";

	memcpy(lu_status->kernel + lu_status->kernel_off, data, size);
	lu_status->kernel_off += size;

	errno = 0;
	return NULL;
}

static const char *lu_arch(const void *ctx, struct connection *conn,
			   char **vec, int num)
{
	if (num == 2 && !strcmp(vec[0], "-b"))
		return lu_binary_alloc(ctx, conn, atol(vec[1]));
	if (num > 2 && !strcmp(vec[0], "-d"))
		return lu_binary_save(ctx, conn, atoi(vec[1]), vec[2]);

	errno = EINVAL;
	return NULL;
}

static FILE *lu_dump_open(const void *ctx)
{
	lu_status->dump_size = ROUNDUP(talloc_total_size(NULL) * 2,
				       XC_PAGE_SHIFT);
	lu_status->dump_state = mmap(NULL, lu_status->dump_size,
				     PROT_READ | PROT_WRITE,
				     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	if (lu_status->dump_state == MAP_FAILED)
		return NULL;

	return fmemopen(lu_status->dump_state, lu_status->dump_size, "w");
}

static void lu_dump_close(FILE *fp)
{
	size_t size;

	size = ftell(fp);
	size = ROUNDUP(size, XC_PAGE_SHIFT);
	munmap(lu_status->dump_state + size, lu_status->dump_size - size);
	lu_status->dump_size = size;

	fclose(fp);
}

static void lu_get_dump_state(struct lu_dump_state *state)
{
}

static void lu_close_dump_state(struct lu_dump_state *state)
{
}

static char *lu_exec(const void *ctx, int argc, char **argv)
{
	return "NYI";
}
#else
static const char *lu_binary(const void *ctx, struct connection *conn,
			     const char *filename)
{
	const char *ret;
	struct stat statbuf;

	syslog(LOG_INFO, "live-update: binary %s\n", filename);

	if (stat(filename, &statbuf))
		return "File not accessible.";
	if (!(statbuf.st_mode & (S_IXOTH | S_IXGRP | S_IXUSR)))
		return "File not executable.";

	ret = lu_begin(conn);
	if (ret)
		return ret;

	lu_status->filename = talloc_strdup(lu_status, filename);
	if (!lu_status->filename)
		return "Allocation failure.";

	errno = 0;
	return NULL;
}

static const char *lu_arch(const void *ctx, struct connection *conn,
			   char **vec, int num)
{
	if (num == 2 && !strcmp(vec[0], "-f"))
		return lu_binary(ctx, conn, vec[1]);

	errno = EINVAL;
	return NULL;
}

static FILE *lu_dump_open(const void *ctx)
{
	char *filename;
	int fd;

	filename = talloc_asprintf(ctx, "%s/state_dump", xs_daemon_rootdir());
	if (!filename)
		return NULL;

	fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
	if (fd < 0)
		return NULL;

	return fdopen(fd, "w");
}

static void lu_dump_close(FILE *fp)
{
	fclose(fp);
}

static void lu_get_dump_state(struct lu_dump_state *state)
{
	struct stat statbuf;

	state->size = 0;

	state->filename = talloc_asprintf(NULL, "%s/state_dump",
					  xs_daemon_rootdir());
	if (!state->filename)
		barf("Allocation failure");

	state->fd = open(state->filename, O_RDONLY);
	if (state->fd < 0)
		return;
	if (fstat(state->fd, &statbuf) != 0)
		goto out_close;
	state->size = statbuf.st_size;

	state->buf = mmap(NULL, state->size, PROT_READ, MAP_PRIVATE,
			  state->fd, 0);
	if (state->buf == MAP_FAILED) {
		state->size = 0;
		goto out_close;
	}

	return;

 out_close:
	close(state->fd);
}

static void lu_close_dump_state(struct lu_dump_state *state)
{
	assert(state->filename != NULL);

	munmap(state->buf, state->size);
	close(state->fd);

	unlink(state->filename);
	talloc_free(state->filename);
}

static char *lu_exec(const void *ctx, int argc, char **argv)
{
	argv[0] = lu_status->filename;
	execvp(argv[0], argv);

	return "Error activating new binary.";
}
#endif

static bool lu_check_lu_allowed(void)
{
	struct connection *conn;
	time_t now = time(NULL);
	unsigned int ta_total = 0, ta_long = 0;

	list_for_each_entry(conn, &connections, list) {
		if (conn->ta_start_time) {
			ta_total++;
			if (now - conn->ta_start_time >= lu_status->timeout)
				ta_long++;
		}
	}

	/*
	 * Allow LiveUpdate if one of the following conditions is met:
	 *	- There is no active transactions
	 *	- All transactions are long running (e.g. they have been
	 *	active for more than lu_status->timeout sec) and the admin as
	 *	requested to force the operation.
	 */
	return ta_total ? (lu_status->force && ta_long == ta_total) : true;
}

static const char *lu_reject_reason(const void *ctx)
{
	char *ret = NULL;
	struct connection *conn;
	time_t now = time(NULL);

	list_for_each_entry(conn, &connections, list) {
		unsigned long tdiff = now - conn->ta_start_time;

		if (conn->ta_start_time && (tdiff >= lu_status->timeout)) {
			ret = talloc_asprintf(ctx, "%s\nDomain %u: %ld s",
					      ret ? : "Domains with long running transactions:",
					      conn->id, tdiff);
		}
	}

	return ret ? (const char *)ret : "Overlapping transactions";
}

static const char *lu_dump_state(const void *ctx, struct connection *conn)
{
	FILE *fp;
	const char *ret;
	struct xs_state_record_header end;
	struct xs_state_preamble pre;

	fp = lu_dump_open(ctx);
	if (!fp)
		return "Dump state open error";

	memcpy(pre.ident, XS_STATE_IDENT, sizeof(pre.ident));
	pre.version = htobe32(XS_STATE_VERSION);
	pre.flags = XS_STATE_FLAGS;
	if (fwrite(&pre, sizeof(pre), 1, fp) != 1) {
		ret = "Dump write error";
		goto out;
	}

	ret = dump_state_global(fp);
	if (ret)
		goto out;
	ret = dump_state_connections(fp);
	if (ret)
		goto out;
	ret = dump_state_nodes(fp, ctx);
	if (ret)
		goto out;

	end.type = XS_STATE_TYPE_END;
	end.length = 0;
	if (fwrite(&end, sizeof(end), 1, fp) != 1)
		ret = "Dump write error";

 out:
	lu_dump_close(fp);

	return ret;
}

void lu_read_state(void)
{
	struct lu_dump_state state = {};
	struct xs_state_record_header *head;
	void *ctx = talloc_new(NULL); /* Work context for subfunctions. */
	struct xs_state_preamble *pre;

	syslog(LOG_INFO, "live-update: read state\n");
	lu_get_dump_state(&state);
	if (state.size == 0)
		barf_perror("No state found after live-update");

	pre = state.buf;
	if (memcmp(pre->ident, XS_STATE_IDENT, sizeof(pre->ident)) ||
	    pre->version != htobe32(XS_STATE_VERSION) ||
	    pre->flags != XS_STATE_FLAGS)
		barf("Unknown record identifier");
	for (head = state.buf + sizeof(*pre);
	     head->type != XS_STATE_TYPE_END &&
		(void *)head - state.buf < state.size;
	     head = (void *)head + sizeof(*head) + head->length) {
		switch (head->type) {
		case XS_STATE_TYPE_GLOBAL:
			read_state_global(ctx, head + 1);
			break;
		case XS_STATE_TYPE_CONN:
			read_state_connection(ctx, head + 1);
			break;
		case XS_STATE_TYPE_WATCH:
			read_state_watch(ctx, head + 1);
			break;
		case XS_STATE_TYPE_TA:
			xprintf("live-update: ignore transaction record\n");
			break;
		case XS_STATE_TYPE_NODE:
			read_state_node(ctx, head + 1);
			break;
		default:
			xprintf("live-update: unknown state record %08x\n",
				head->type);
			break;
		}
	}

	lu_close_dump_state(&state);

	talloc_free(ctx);

	/*
	 * We may have missed the VIRQ_DOM_EXC notification and a domain may
	 * have died while we were live-updating. So check all the domains are
	 * still alive.
	 */
	check_domains();
}

static const char *lu_activate_binary(const void *ctx)
{
	int argc;
	char **argv;
	unsigned int i;

	if (lu_status->cmdline) {
		argc = 4;   /* At least one arg + progname + "-U" + NULL. */
		for (i = 0; lu_status->cmdline[i]; i++)
			if (isspace(lu_status->cmdline[i]))
				argc++;
		argv = talloc_array(ctx, char *, argc);
		if (!argv)
			return "Allocation failure.";

		i = 0;
		argc = 1;
		argv[1] = strtok(lu_status->cmdline, " \t");
		while (argv[argc]) {
			if (!strcmp(argv[argc], "-U"))
				i = 1;
			argc++;
			argv[argc] = strtok(NULL, " \t");
		}

		if (!i) {
			argv[argc++] = "-U";
			argv[argc] = NULL;
		}
	} else {
		for (i = 0; i < orig_argc; i++)
			if (!strcmp(orig_argv[i], "-U"))
				break;

		argc = orig_argc;
		argv = talloc_array(ctx, char *, orig_argc + 2);
		if (!argv)
			return "Allocation failure.";

		memcpy(argv, orig_argv, orig_argc * sizeof(*argv));
		if (i == orig_argc)
			argv[argc++] = "-U";
		argv[argc] = NULL;
	}

	domain_deinit();

	return lu_exec(ctx, argc, argv);
}

static bool do_lu_start(struct delayed_request *req)
{
	time_t now = time(NULL);
	const char *ret;
	struct buffered_data *saved_in;
	struct connection *conn = req->data;

	/*
	 * Cancellation may have been requested asynchronously. In this
	 * case, lu_status will be NULL.
	 */
	if (!lu_status) {
		ret = "Cancellation was requested";
		goto out;
	}

	assert(lu_status->conn == conn);

	if (!lu_check_lu_allowed()) {
		if (now < lu_status->started_at + lu_status->timeout)
			return false;
		if (!lu_status->force) {
			ret = lu_reject_reason(req);
			goto out;
		}
	}

	assert(req->in == lu_status->in);
	/* Dump out internal state, including "OK" for live update. */
	ret = lu_dump_state(req->in, conn);
	if (!ret) {
		/* Perform the activation of new binary. */
		ret = lu_activate_binary(req->in);
	}

	/* We will reach this point only in case of failure. */
 out:
	/*
	 * send_reply() will send the response for conn->in. Save the current
	 * conn->in and restore it afterwards.
	 */
	saved_in = conn->in;
	conn->in = req->in;
	send_reply(conn, XS_CONTROL, ret, strlen(ret) + 1);
	conn->in = saved_in;
	talloc_free(lu_status);

	return true;
}

static const char *lu_start(const void *ctx, struct connection *conn,
			    bool force, unsigned int to)
{
	syslog(LOG_INFO, "live-update: start, force=%d, to=%u\n", force, to);

	if (!lu_status || lu_status->conn != conn)
		return "Not in live-update session.";

#ifdef __MINIOS__
	if (lu_status->kernel_size != lu_status->kernel_off)
		return "Kernel not complete.";
#endif

	lu_status->force = force;
	lu_status->timeout = to;
	lu_status->started_at = time(NULL);
	lu_status->in = conn->in;

	errno = delay_request(conn, conn->in, do_lu_start, conn, false);

	return NULL;
}

static int do_control_lu(const void *ctx, struct connection *conn,
			 char **vec, int num)
{
	const char *ret = NULL;
	unsigned int i;
	bool force = false;
	unsigned int to = 0;

	if (num < 1)
		return EINVAL;

	if (!strcmp(vec[0], "-a")) {
		if (num == 1)
			ret = lu_abort(ctx, conn);
		else
			return EINVAL;
	} else if (!strcmp(vec[0], "-c")) {
		if (num == 2)
			ret = lu_cmdline(ctx, conn, vec[1]);
		else
			return EINVAL;
	} else if (!strcmp(vec[0], "-s")) {
		for (i = 1; i < num; i++) {
			if (!strcmp(vec[i], "-F"))
				force = true;
			else if (!strcmp(vec[i], "-t") && i < num - 1) {
				i++;
				to = atoi(vec[i]);
			} else
				return EINVAL;
		}
		ret = lu_start(ctx, conn, force, to);
		if (!ret)
			return errno;
	} else {
		ret = lu_arch(ctx, conn, vec, num);
		if (!ret && errno)
			return errno;
	}

	if (!ret)
		ret = "OK";
	send_reply(conn, XS_CONTROL, ret, strlen(ret) + 1);
	return 0;
}
#endif

static int do_control_help(const void *, struct connection *, char **, int);

static struct cmd_s cmds[] = {
	{ "check", do_control_check, "" },
	{ "log", do_control_log, "[on|off|+<switch>|-<switch>]" },

#ifndef NO_LIVE_UPDATE
	/*
	 * The parameters are those of the xenstore-control utility!
	 * Depending on environment (Mini-OS or daemon) the live-update
	 * sequence is split into several sub-operations:
	 * 1. Specification of new binary
	 *    daemon:  -f <filename>
	 *    Mini-OS: -b <binary-size>
	 *             -d <size> <data-bytes> (multiple of those)
	 * 2. New command-line (optional): -c <cmdline>
	 * 3. Start of update: -s [-F] [-t <timeout>]
	 * Any sub-operation needs to respond with the string "OK" in case
	 * of success, any other response indicates failure.
	 * A started live-update sequence can be aborted via "-a" (not
	 * needed in case of failure for the first or last live-update
	 * sub-operation).
	 */
	{ "live-update", do_control_lu,
		"[-c <cmdline>] [-F] [-t <timeout>] <file>\n"
		"    Default timeout is 60 seconds.", 5 },
#endif
#ifdef __MINIOS__
	{ "memreport", do_control_memreport, "" },
#else
	{ "logfile", do_control_logfile, "<file>" },
	{ "memreport", do_control_memreport, "[<file>]" },
#endif
	{ "print", do_control_print, "<string>" },
	{ "quota", do_control_quota, "[set <name> <val>|<domid>]" },
	{ "quota-soft", do_control_quota_s, "[set <name> <val>]" },
	{ "help", do_control_help, "" },
};

static int do_control_help(const void *ctx, struct connection *conn,
			   char **vec, int num)
{
	int cmd;
	char *resp;

	if (num)
		return EINVAL;

	resp = talloc_asprintf(ctx, "%s", "");
	if (!resp)
		return ENOMEM;
	for (cmd = 0; cmd < ARRAY_SIZE(cmds); cmd++) {
		resp = talloc_asprintf_append(resp, "%-15s %s\n",
					      cmds[cmd].cmd, cmds[cmd].pars);
		if (!resp)
			return ENOMEM;
	}

	send_reply(conn, XS_CONTROL, resp, strlen(resp) + 1);
	return 0;
}

int do_control(const void *ctx, struct connection *conn,
	       struct buffered_data *in)
{
	unsigned int cmd, num, off;
	char **vec = NULL;

	if (domain_is_unprivileged(conn))
		return EACCES;

	off = get_string(in, 0);
	if (!off)
		return EINVAL;
	for (cmd = 0; cmd < ARRAY_SIZE(cmds); cmd++)
		if (streq(in->buffer, cmds[cmd].cmd))
			break;
	if (cmd == ARRAY_SIZE(cmds))
		return EINVAL;

	num = xs_count_strings(in->buffer, in->used);
	if (cmds[cmd].max_pars)
		num = min(num, cmds[cmd].max_pars);
	vec = talloc_array(ctx, char *, num);
	if (!vec)
		return ENOMEM;
	if (get_strings(in, vec, num) < num)
		return EIO;

	return cmds[cmd].func(ctx, conn, vec + 1, num - 1);
}