path: root/tools/xenstore/xs.c

/* 
    Xen Store Daemon interface providing simple tree-like database.
    Copyright (C) 2005 Rusty Russell IBM Corporation

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library 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
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <string.h>
#include <unistd.h>
#include <stdbool.h>
#include <stdlib.h>
#include <assert.h>
#include <stdio.h>
#include <signal.h>
#include <stdint.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <pthread.h>
#include "xs.h"
#include "list.h"
#include "utils.h"

struct xs_stored_msg {
	struct list_head list;
	struct xsd_sockmsg hdr;
	char *body;
};

struct xs_handle {
	/* Communications channel to xenstore daemon. */
	int fd;

	/*
         * A read thread which pulls messages off the comms channel and
         * signals waiters.
         */
	pthread_t read_thr;

	/*
         * A list of fired watch messages, protected by a mutex. Users can
         * wait on the conditional variable until a watch is pending.
         */
	struct list_head watch_list;
	pthread_mutex_t watch_mutex;
	pthread_cond_t watch_condvar;

	/* Clients can select() on this pipe to wait for a watch to fire. */
	int watch_pipe[2];

	/*
         * A list of replies. Currently only one will ever be outstanding
         * because we serialise requests. The requester can wait on the
         * conditional variable for its response.
         */
	struct list_head reply_list;
	pthread_mutex_t reply_mutex;
	pthread_cond_t reply_condvar;

	/* One request at a time. */
	pthread_mutex_t request_mutex;

	/* One transaction at a time. */
	pthread_mutex_t transaction_mutex;
};

static void *read_thread(void *arg);

int xs_fileno(struct xs_handle *h)
{
	char c = 0;

	pthread_mutex_lock(&h->watch_mutex);

	if ((h->watch_pipe[0] == -1) && (pipe(h->watch_pipe) != -1)) {
		/* Kick things off if the watch list is already non-empty. */
		if (!list_empty(&h->watch_list))
			while (write(h->watch_pipe[1], &c, 1) != 1)
				continue;
	}

	pthread_mutex_unlock(&h->watch_mutex);

	return h->watch_pipe[0];
}

static int get_socket(const char *connect_to)
{
	struct sockaddr_un addr;
	int sock, saved_errno;

	sock = socket(PF_UNIX, SOCK_STREAM, 0);
	if (sock < 0)
		return -1;

	addr.sun_family = AF_UNIX;
	strcpy(addr.sun_path, connect_to);

	if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) != 0) {
		saved_errno = errno;
		close(sock);
		errno = saved_errno;
		return -1;
	}

	return sock;
}

static int get_dev(const char *connect_to)
{
	return open(connect_to, O_RDWR);
}

static struct xs_handle *get_handle(const char *connect_to)
{
	struct stat buf;
	struct xs_handle *h = NULL;
	int fd = -1, saved_errno;

	if (stat(connect_to, &buf) != 0)
		goto error;

	if (S_ISSOCK(buf.st_mode))
		fd = get_socket(connect_to);
	else
		fd = get_dev(connect_to);

	if (fd == -1)
		goto error;

	h = malloc(sizeof(*h));
	if (h == NULL)
		goto error;

	h->fd = fd;

	/* Watch pipe is allocated on demand in xs_fileno(). */
	h->watch_pipe[0] = h->watch_pipe[1] = -1;

	INIT_LIST_HEAD(&h->watch_list);
	pthread_mutex_init(&h->watch_mutex, NULL);
	pthread_cond_init(&h->watch_condvar, NULL);

	INIT_LIST_HEAD(&h->reply_list);
	pthread_mutex_init(&h->reply_mutex, NULL);
	pthread_cond_init(&h->reply_condvar, NULL);

	pthread_mutex_init(&h->request_mutex, NULL);
	pthread_mutex_init(&h->transaction_mutex, NULL);

	if (pthread_create(&h->read_thr, NULL, read_thread, h) != 0)
		goto error;

	return h;

 error:
	saved_errno = errno;
	if (h != NULL)
		free(h);
	if (fd != -1)
		close(fd);
	errno = saved_errno;
	return NULL;
}

struct xs_handle *xs_daemon_open(void)
{
	return get_handle(xs_daemon_socket());
}

struct xs_handle *xs_daemon_open_readonly(void)
{
	return get_handle(xs_daemon_socket_ro());
}

struct xs_handle *xs_domain_open(void)
{
	return get_handle(xs_domain_dev());
}

void xs_daemon_close(struct xs_handle *h)
{
	struct xs_stored_msg *msg, *tmsg;

	pthread_mutex_lock(&h->transaction_mutex);
	pthread_mutex_lock(&h->request_mutex);
	pthread_mutex_lock(&h->reply_mutex);
	pthread_mutex_lock(&h->watch_mutex);

	/* XXX FIXME: May leak an unpublished message buffer. */
	pthread_cancel(h->read_thr);
	pthread_join(h->read_thr, NULL);

	list_for_each_entry_safe(msg, tmsg, &h->reply_list, list) {
		free(msg->body);
		free(msg);
	}

	list_for_each_entry_safe(msg, tmsg, &h->watch_list, list) {
		free(msg->body);
		free(msg);
	}

	pthread_mutex_unlock(&h->transaction_mutex);
	pthread_mutex_unlock(&h->request_mutex);
	pthread_mutex_unlock(&h->reply_mutex);
	pthread_mutex_unlock(&h->watch_mutex);

	if (h->watch_pipe[0] != -1) {
		close(h->watch_pipe[0]);
		close(h->watch_pipe[1]);
	}

	close(h->fd);

	free(h);
}

static bool read_all(int fd, void *data, unsigned int len)
{
	while (len) {
		int done;

		done = read(fd, data, len);
		if (done < 0) {
			if (errno == EINTR)
				continue;
			return false;
		}
		if (done == 0) {
			/* It closed fd on us?  EBADF is appropriate. */
			errno = EBADF;
			return false;
		}
		data += done;
		len -= done;
	}

	return true;
}

#ifdef XSTEST
#define read_all read_all_choice
#define xs_write_all write_all_choice
#endif

static int get_error(const char *errorstring)
{
	unsigned int i;

	for (i = 0; !streq(errorstring, xsd_errors[i].errstring); i++)
		if (i == ARRAY_SIZE(xsd_errors) - 1)
			return EINVAL;
	return xsd_errors[i].errnum;
}

/* Adds extra nul terminator, because we generally (always?) hold strings. */
static void *read_reply(
	struct xs_handle *h, enum xsd_sockmsg_type *type, unsigned int *len)
{
	struct xs_stored_msg *msg;
	char *body;

	pthread_mutex_lock(&h->reply_mutex);
	while (list_empty(&h->reply_list))
		pthread_cond_wait(&h->reply_condvar, &h->reply_mutex);
	msg = list_top(&h->reply_list, struct xs_stored_msg, list);
	list_del(&msg->list);
	assert(list_empty(&h->reply_list));
	pthread_mutex_unlock(&h->reply_mutex);

	*type = msg->hdr.type;
	if (len)
		*len = msg->hdr.len;
	body = msg->body;

	free(msg);

	return body;
}

/* Send message to xs, get malloc'ed reply.  NULL and set errno on error. */
static void *xs_talkv(struct xs_handle *h, enum xsd_sockmsg_type type,
		      const struct iovec *iovec, unsigned int num_vecs,
		      unsigned int *len)
{
	struct xsd_sockmsg msg;
	void *ret = NULL;
	int saved_errno;
	unsigned int i;
	struct sigaction ignorepipe, oldact;

	msg.type = type;
	msg.len = 0;
	for (i = 0; i < num_vecs; i++)
		msg.len += iovec[i].iov_len;

	ignorepipe.sa_handler = SIG_IGN;
	sigemptyset(&ignorepipe.sa_mask);
	ignorepipe.sa_flags = 0;
	sigaction(SIGPIPE, &ignorepipe, &oldact);

	pthread_mutex_lock(&h->request_mutex);

	if (!xs_write_all(h->fd, &msg, sizeof(msg)))
		goto fail;

	for (i = 0; i < num_vecs; i++)
		if (!xs_write_all(h->fd, iovec[i].iov_base, iovec[i].iov_len))
			goto fail;

	ret = read_reply(h, &msg.type, len);
	if (!ret)
		goto fail;

	pthread_mutex_unlock(&h->request_mutex);

	sigaction(SIGPIPE, &oldact, NULL);
	if (msg.type == XS_ERROR) {
		saved_errno = get_error(ret);
		free(ret);
		errno = saved_errno;
		return NULL;
	}

	if (msg.type != type) {
		free(ret);
		saved_errno = EBADF;
		goto close_fd;
		
	}
	return ret;

fail:
	/* We're in a bad state, so close fd. */
	saved_errno = errno;
	pthread_mutex_unlock(&h->request_mutex);
	sigaction(SIGPIPE, &oldact, NULL);
close_fd:
	close(h->fd);
	h->fd = -1;
	errno = saved_errno;
	return NULL;
}

/* free(), but don't change errno. */
static void free_no_errno(void *p)
{
	int saved_errno = errno;
	free(p);
	errno = saved_errno;
}

/* Simplified version of xs_talkv: single message. */
static void *xs_single(struct xs_handle *h, enum xsd_sockmsg_type type,
		       const char *string, unsigned int *len)
{
	struct iovec iovec;

	iovec.iov_base = (void *)string;
	iovec.iov_len = strlen(string) + 1;
	return xs_talkv(h, type, &iovec, 1, len);
}

static bool xs_bool(char *reply)
{
	if (!reply)
		return false;
	free(reply);
	return true;
}

char **xs_directory(struct xs_handle *h, const char *path, unsigned int *num)
{
	char *strings, *p, **ret;
	unsigned int len;

	strings = xs_single(h, XS_DIRECTORY, path, &len);
	if (!strings)
		return NULL;

	/* Count the strings. */
	*num = xs_count_strings(strings, len);

	/* Transfer to one big alloc for easy freeing. */
	ret = malloc(*num * sizeof(char *) + len);
	if (!ret) {
		free_no_errno(strings);
		return NULL;
	}
	memcpy(&ret[*num], strings, len);
	free_no_errno(strings);

	strings = (char *)&ret[*num];
	for (p = strings, *num = 0; p < strings + len; p += strlen(p) + 1)
		ret[(*num)++] = p;
	return ret;
}

/* Get the value of a single file, nul terminated.
 * Returns a malloced value: call free() on it after use.
 * len indicates length in bytes, not including the nul.
 */
void *xs_read(struct xs_handle *h, const char *path, unsigned int *len)
{
	return xs_single(h, XS_READ, path, len);
}

/* Write the value of a single file.
 * Returns false on failure.
 */
bool xs_write(struct xs_handle *h, const char *path,
	      const void *data, unsigned int len)
{
	struct iovec iovec[2];

	iovec[0].iov_base = (void *)path;
	iovec[0].iov_len = strlen(path) + 1;
	iovec[1].iov_base = (void *)data;
	iovec[1].iov_len = len;

	return xs_bool(xs_talkv(h, XS_WRITE, iovec, ARRAY_SIZE(iovec), NULL));
}

/* Create a new directory.
 * Returns false on failure, or success if it already exists.
 */
bool xs_mkdir(struct xs_handle *h, const char *path)
{
	return xs_bool(xs_single(h, XS_MKDIR, path, NULL));
}

/* Destroy a file or directory (directories must be empty).
 * Returns false on failure, or success if it doesn't exist.
 */
bool xs_rm(struct xs_handle *h, const char *path)
{
	return xs_bool(xs_single(h, XS_RM, path, NULL));
}

/* Get permissions of node (first element is owner).
 * Returns malloced array, or NULL: call free() after use.
 */
struct xs_permissions *xs_get_permissions(struct xs_handle *h,
					  const char *path, unsigned int *num)
{
	char *strings;
	unsigned int len;
	struct xs_permissions *ret;

	strings = xs_single(h, XS_GET_PERMS, path, &len);
	if (!strings)
		return NULL;

	/* Count the strings: each one perms then domid. */
	*num = xs_count_strings(strings, len);

	/* Transfer to one big alloc for easy freeing. */
	ret = malloc(*num * sizeof(struct xs_permissions));
	if (!ret) {
		free_no_errno(strings);
		return NULL;
	}

	if (!xs_strings_to_perms(ret, *num, strings)) {
		free_no_errno(ret);
		ret = NULL;
	}

	free(strings);
	return ret;
}

/* Set permissions of node (must be owner).
 * Returns false on failure.
 */
bool xs_set_permissions(struct xs_handle *h, const char *path,
			struct xs_permissions *perms,
			unsigned int num_perms)
{
	unsigned int i;
	struct iovec iov[1+num_perms];

	iov[0].iov_base = (void *)path;
	iov[0].iov_len = strlen(path) + 1;
	
	for (i = 0; i < num_perms; i++) {
		char buffer[MAX_STRLEN(domid_t)+1];

		if (!xs_perm_to_string(&perms[i], buffer))
			goto unwind;

		iov[i+1].iov_base = strdup(buffer);
		iov[i+1].iov_len = strlen(buffer) + 1;
		if (!iov[i+1].iov_base)
			goto unwind;
	}

	if (!xs_bool(xs_talkv(h, XS_SET_PERMS, iov, 1+num_perms, NULL)))
		goto unwind;
	for (i = 0; i < num_perms; i++)
		free(iov[i+1].iov_base);
	return true;

unwind:
	num_perms = i;
	for (i = 0; i < num_perms; i++)
		free_no_errno(iov[i+1].iov_base);
	return false;
}

/* Watch a node for changes (poll on fd to detect, or call read_watch()).
 * When the node (or any child) changes, fd will become readable.
 * Token is returned when watch is read, to allow matching.
 * Returns false on failure.
 */
bool xs_watch(struct xs_handle *h, const char *path, const char *token)
{
	struct iovec iov[2];

	iov[0].iov_base = (void *)path;
	iov[0].iov_len = strlen(path) + 1;
	iov[1].iov_base = (void *)token;
	iov[1].iov_len = strlen(token) + 1;

	return xs_bool(xs_talkv(h, XS_WATCH, iov, ARRAY_SIZE(iov), NULL));
}

/* Find out what node change was on (will block if nothing pending).
 * Returns array of two pointers: path and token, or NULL.
 * Call free() after use.
 */
char **xs_read_watch(struct xs_handle *h, unsigned int *num)
{
	struct xs_stored_msg *msg;
	char **ret, *strings, c = 0;
	unsigned int num_strings, i;

	pthread_mutex_lock(&h->watch_mutex);

	/* Wait on the condition variable for a watch to fire. */
	while (list_empty(&h->watch_list))
		pthread_cond_wait(&h->watch_condvar, &h->watch_mutex);
	msg = list_top(&h->watch_list, struct xs_stored_msg, list);
	list_del(&msg->list);

	/* Clear the pipe token if there are no more pending watches. */
	if (list_empty(&h->watch_list) && (h->watch_pipe[0] != -1))
		while (read(h->watch_pipe[0], &c, 1) != 1)
			continue;

	pthread_mutex_unlock(&h->watch_mutex);

	assert(msg->hdr.type == XS_WATCH_EVENT);

	strings     = msg->body;
	num_strings = xs_count_strings(strings, msg->hdr.len);

	ret = malloc(sizeof(char*) * num_strings + msg->hdr.len);
	if (!ret) {
		free_no_errno(strings);
		free_no_errno(msg);
		return NULL;
	}

	ret[0] = (char *)(ret + num_strings);
	memcpy(ret[0], strings, msg->hdr.len);

	free(strings);
	free(msg);

	for (i = 1; i < num_strings; i++)
		ret[i] = ret[i - 1] + strlen(ret[i - 1]) + 1;

	*num = num_strings;

	return ret;
}

/* Acknowledge watch on node.  Watches must be acknowledged before
 * any other watches can be read.
 * Returns false on failure.
 */
bool xs_acknowledge_watch(struct xs_handle *h, const char *token)
{
	return xs_bool(xs_single(h, XS_WATCH_ACK, token, NULL));
}

/* Remove a watch on a node.
 * Returns false on failure (no watch on that node).
 */
bool xs_unwatch(struct xs_handle *h, const char *path, const char *token)
{
	struct iovec iov[2];

	iov[0].iov_base = (char *)path;
	iov[0].iov_len = strlen(path) + 1;
	iov[1].iov_base = (char *)token;
	iov[1].iov_len = strlen(token) + 1;

	return xs_bool(xs_talkv(h, XS_UNWATCH, iov, ARRAY_SIZE(iov), NULL));
}

/* Start a transaction: changes by others will not be seen during this
 * transaction, and changes will not be visible to others until end.
 * You can only have one transaction at any time.
 * Returns false on failure.
 */
bool xs_transaction_start(struct xs_handle *h)
{
	pthread_mutex_lock(&h->transaction_mutex);
	return xs_bool(xs_single(h, XS_TRANSACTION_START, "", NULL));
}

/* End a transaction.
 * If abandon is true, transaction is discarded instead of committed.
 * Returns false on failure, which indicates an error: transactions will
 * not fail spuriously.
 */
bool xs_transaction_end(struct xs_handle *h, bool abort)
{
	char abortstr[2];
	bool rc;

	if (abort)
		strcpy(abortstr, "F");
	else
		strcpy(abortstr, "T");
	
	rc = xs_bool(xs_single(h, XS_TRANSACTION_END, abortstr, NULL));

	pthread_mutex_unlock(&h->transaction_mutex);

	return rc;
}

/* Introduce a new domain.
 * This tells the store daemon about a shared memory page and event channel
 * associated with a domain: the domain uses these to communicate.
 */
bool xs_introduce_domain(struct xs_handle *h, domid_t domid, unsigned long mfn,
			 unsigned int eventchn, const char *path)
{
	char domid_str[MAX_STRLEN(domid)];
	char mfn_str[MAX_STRLEN(mfn)];
	char eventchn_str[MAX_STRLEN(eventchn)];
	struct iovec iov[4];

	sprintf(domid_str, "%u", domid);
	sprintf(mfn_str, "%lu", mfn);
	sprintf(eventchn_str, "%u", eventchn);

	iov[0].iov_base = domid_str;
	iov[0].iov_len = strlen(domid_str) + 1;
	iov[1].iov_base = mfn_str;
	iov[1].iov_len = strlen(mfn_str) + 1;
	iov[2].iov_base = eventchn_str;
	iov[2].iov_len = strlen(eventchn_str) + 1;
	iov[3].iov_base = (char *)path;
	iov[3].iov_len = strlen(path) + 1;

	return xs_bool(xs_talkv(h, XS_INTRODUCE, iov, ARRAY_SIZE(iov), NULL));
}

bool xs_release_domain(struct xs_handle *h, domid_t domid)
{
	char domid_str[MAX_STRLEN(domid)];

	sprintf(domid_str, "%u", domid);

	return xs_bool(xs_single(h, XS_RELEASE, domid_str, NULL));
}

char *xs_get_domain_path(struct xs_handle *h, domid_t domid)
{
	char domid_str[MAX_STRLEN(domid)];

	sprintf(domid_str, "%u", domid);

	return xs_single(h, XS_GET_DOMAIN_PATH, domid_str, NULL);
}

/* Only useful for DEBUG versions */
char *xs_debug_command(struct xs_handle *h, const char *cmd,
		       void *data, unsigned int len)
{
	struct iovec iov[2];

	iov[0].iov_base = (void *)cmd;
	iov[0].iov_len = strlen(cmd) + 1;
	iov[1].iov_base = data;
	iov[1].iov_len = len;

	return xs_talkv(h, XS_DEBUG, iov, ARRAY_SIZE(iov), NULL);
}

static void *read_thread(void *arg)
{
	struct xs_handle *h = arg;
	struct xs_stored_msg *msg = NULL;
	char *body = NULL;

	for (;;) {
		msg = NULL;
		body = NULL;

		/* Allocate message structure and read the message header. */
		msg = malloc(sizeof(*msg));
		if (msg == NULL)
			goto error;
		if (!read_all(h->fd, &msg->hdr, sizeof(msg->hdr)))
			goto error;

		/* Allocate and read the message body. */
		body = msg->body = malloc(msg->hdr.len + 1);
		if (body == NULL)
			goto error;
		if (!read_all(h->fd, body, msg->hdr.len))
			goto error;
		body[msg->hdr.len] = '\0';

		if (msg->hdr.type == XS_WATCH_EVENT) {
			pthread_mutex_lock(&h->watch_mutex);

			/* Kick users out of their select() loop. */
			if (list_empty(&h->watch_list) &&
			    (h->watch_pipe[1] != -1))
				while (write(h->watch_pipe[1], body, 1) != 1)
					continue;

			list_add_tail(&msg->list, &h->watch_list);
			pthread_cond_signal(&h->watch_condvar);

			pthread_mutex_unlock(&h->watch_mutex);
		} else {
			pthread_mutex_lock(&h->reply_mutex);

			/* There should only ever be one response pending! */
			if (!list_empty(&h->reply_list)) {
				pthread_mutex_unlock(&h->reply_mutex);
				goto error;
			}

			list_add_tail(&msg->list, &h->reply_list);
			pthread_cond_signal(&h->reply_condvar);

			pthread_mutex_unlock(&h->reply_mutex);
		}
	}

 error:
	if (body != NULL)
		free(body);
	if (msg != NULL)
		free(msg);
	return NULL;
}

/*
 * Local variables:
 *  c-file-style: "linux"
 *  indent-tabs-mode: t
 *  c-indent-level: 8
 *  c-basic-offset: 8
 *  tab-width: 8
 * End:
 */