Date:	Tue, 26 Mar 2013 10:02:26 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
CC:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	jasowang@...hat.com, Evgeniy Polyakov <zbr@...emap.net>
Subject: Re: [PATCH V2 1/1] Drivers: hv: Add a new driver to support host
 initiated backup

> diff --git a/tools/hv/hv_vss_daemon.c b/tools/hv/hv_vss_daemon.c
> new file mode 100644
> index 0000000..9526995
> --- /dev/null
> +++ b/tools/hv/hv_vss_daemon.c
> @@ -0,0 +1,220 @@
> +/*
> + * An implementation of the host initiated guest snapshot for Hyper-V.
> + *
> + *
> + * Copyright (C) 2013, Microsoft, Inc.
> + * Author : K. Y. Srinivasan <kys@...rosoft.com>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published
> + * by the Free Software Foundation.
> + *
> + * 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, GOOD TITLE or
> + * NON INFRINGEMENT.  See the GNU General Public License for more
> + * details.
> + *
> + */
> +
> +
> +#include <sys/types.h>
> +#include <sys/socket.h>
> +#include <sys/poll.h>
> +#include <linux/types.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include <string.h>
> +#include <ctype.h>
> +#include <errno.h>
> +#include <arpa/inet.h>
> +#include <linux/connector.h>
> +#include <linux/hyperv.h>
> +#include <linux/netlink.h>
> +#include <syslog.h>
> +
> +static char vss_recv_buffer[4096];
> +static char vss_send_buffer[4096];
> +static struct sockaddr_nl addr;
> +
> +#ifndef SOL_NETLINK
> +#define SOL_NETLINK 270
> +#endif
> +
> +
> +static int vss_operate(int operation)
> +{
> +	char *fs_op;
> +	char cmd[512];
> +	char buf[512];
> +	FILE *file;
> +	char *p;
> +	char *x;
> +	int error;
> +
> +	switch (operation) {
> +	case VSS_OP_FREEZE:
> +		fs_op = "-f ";
> +		break;
> +	case VSS_OP_THAW:
> +		fs_op = "-u ";
> +		break;
> +	}
> +
> +	file = popen("mount | awk '/^\/dev\// { print $3}'", "r");
> +	if (file == NULL)
> +		return;
> +
> +	while ((p = fgets(buf, sizeof(buf), file)) != NULL) {
> +		x = strchr(p, '\n');
> +		*x = '\0';
> +		if (!strncmp(p, "/", sizeof("/")))
> +			continue;
> +
> +		sprintf(cmd, "%s %s %s", "fsfreeze ", fs_op, p);

Please use getmntent and FIFREEZE/FITHAW.

However, I wonder if a dedicated daemon is really the best mechanism.
Perhaps you can use uevents instead, and trigger the freeze/thaw with
udev rules?

Paolo

> +		syslog(LOG_INFO, "VSS cmd is %s\n", cmd);
> +		error = system(cmd);
> +	}
> +	pclose(file);
> +
> +	sprintf(cmd, "%s %s %s", "fsfreeze ", fs_op, "/");
> +	syslog(LOG_INFO, "VSS cmd is %s\n", cmd);
> +	error = system(cmd);
> +
> +	return error;
> +}
> +
> +static int netlink_send(int fd, struct cn_msg *msg)
> +{
> +	struct nlmsghdr *nlh;
> +	unsigned int size;
> +	struct msghdr message;
> +	char buffer[64];
> +	struct iovec iov[2];
> +
> +	size = NLMSG_SPACE(sizeof(struct cn_msg) + msg->len);
> +
> +	nlh = (struct nlmsghdr *)buffer;
> +	nlh->nlmsg_seq = 0;
> +	nlh->nlmsg_pid = getpid();
> +	nlh->nlmsg_type = NLMSG_DONE;
> +	nlh->nlmsg_len = NLMSG_LENGTH(size - sizeof(*nlh));
> +	nlh->nlmsg_flags = 0;
> +
> +	iov[0].iov_base = nlh;
> +	iov[0].iov_len = sizeof(*nlh);
> +
> +	iov[1].iov_base = msg;
> +	iov[1].iov_len = size;
> +
> +	memset(&message, 0, sizeof(message));
> +	message.msg_name = &addr;
> +	message.msg_namelen = sizeof(addr);
> +	message.msg_iov = iov;
> +	message.msg_iovlen = 2;
> +
> +	return sendmsg(fd, &message, 0);
> +}
> +
> +int main(void)
> +{
> +	int fd, len, nl_group;
> +	int error;
> +	struct cn_msg *message;
> +	struct pollfd pfd;
> +	struct nlmsghdr *incoming_msg;
> +	struct cn_msg	*incoming_cn_msg;
> +	int	op;
> +	struct hv_vss_msg *vss_msg;
> +
> +	daemon(1, 0);
> +	openlog("Hyper-V VSS", 0, LOG_USER);
> +	syslog(LOG_INFO, "VSS starting; pid is:%d", getpid());
> +
> +	fd = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
> +	if (fd < 0) {
> +		syslog(LOG_ERR, "netlink socket creation failed; error:%d", fd);
> +		exit(EXIT_FAILURE);
> +	}
> +	addr.nl_family = AF_NETLINK;
> +	addr.nl_pad = 0;
> +	addr.nl_pid = 0;
> +	addr.nl_groups = 0;
> +
> +
> +	error = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
> +	if (error < 0) {
> +		syslog(LOG_ERR, "bind failed; error:%d", error);
> +		close(fd);
> +		exit(EXIT_FAILURE);
> +	}
> +	nl_group = CN_VSS_IDX;
> +	setsockopt(fd, SOL_NETLINK, NETLINK_ADD_MEMBERSHIP, &nl_group, sizeof(nl_group));
> +	/*
> +	 * Register ourselves with the kernel.
> +	 */
> +	message = (struct cn_msg *)vss_send_buffer;
> +	message->id.idx = CN_VSS_IDX;
> +	message->id.val = CN_VSS_VAL;
> +	message->ack = 0;
> +	vss_msg = (struct hv_vss_msg *)message->data;
> +	vss_msg->vss_hdr.operation = VSS_OP_REGISTER;
> +
> +	message->len = sizeof(struct hv_vss_msg);
> +
> +	len = netlink_send(fd, message);
> +	if (len < 0) {
> +		syslog(LOG_ERR, "netlink_send failed; error:%d", len);
> +		close(fd);
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	pfd.fd = fd;
> +
> +	while (1) {
> +		struct sockaddr *addr_p = (struct sockaddr *) &addr;
> +		socklen_t addr_l = sizeof(addr);
> +		pfd.events = POLLIN;
> +		pfd.revents = 0;
> +		poll(&pfd, 1, -1);
> +
> +		len = recvfrom(fd, vss_recv_buffer, sizeof(vss_recv_buffer), 0,
> +				addr_p, &addr_l);
> +
> +		if (len < 0 || addr.nl_pid) {
> +			syslog(LOG_ERR, "recvfrom failed; pid:%u error:%d %s",
> +					addr.nl_pid, errno, strerror(errno));
> +			close(fd);
> +			return -1;
> +		}
> +
> +		incoming_msg = (struct nlmsghdr *)vss_recv_buffer;
> +
> +		if (incoming_msg->nlmsg_type != NLMSG_DONE)
> +			continue;
> +
> +		incoming_cn_msg = (struct cn_msg *)NLMSG_DATA(incoming_msg);
> +		vss_msg = (struct hv_vss_msg *)incoming_cn_msg->data;
> +		op = vss_msg->vss_hdr.operation;
> +		error =  HV_S_OK;
> +
> +		switch (op) {
> +		case VSS_OP_FREEZE:
> +		case VSS_OP_THAW:
> +			error = vss_operate(op);
> +			if (error)
> +				error = HV_E_FAIL;
> +			break;
> +		default:
> +			syslog(LOG_ERR, "Illegal op:%d\n", op);
> +		}
> +		vss_msg->error = error;
> +		len = netlink_send(fd, incoming_cn_msg);
> +		if (len < 0) {
> +			syslog(LOG_ERR, "net_link send failed; error:%d", len);
> +			exit(EXIT_FAILURE);
> +		}
> +	}
> +
> +}
> 

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