cf8bc16b1e
VSS stands for "Volume Shadow Copy Service". Unlike virtual machine
snapshot, it only takes snapshot for the virtual disks, so both
filesystem and applications have to aware of it, and cooperate the
whole VSS process.
This driver exposes two device files to the userland:
/dev/hv_fsvss_dev
Normally userland programs should _not_ mess with this device file.
It is currently used by the hv_vss_daemon(8), which freezes and
thaws the filesystem. NOTE: currently only UFS is supported, if
the system mounts _any_ other filesystems, the hv_vss_daemon(8)
will veto the VSS process.
If hv_vss_daemon(8) was disabled, then this device file must be
opened, and proper ioctls must be issued to keep the VSS working.
/dev/hv_appvss_dev
Userland application can opened this device file to receive the
VSS freeze notification, hold the VSS for a while (mainly to flush
application data to filesystem), release the VSS process, and
receive the VSS thaw notification i.e. applications can run again.
The VSS will still work, even if this device file is not opened.
However, only filesystem consistency is promised, if this device
file is not opened or is not operated properly.
hv_vss_daemon(8) is started by devd(8) by default. It can be disabled
by editting /etc/devd/hyperv.conf.
Submitted by: Hongjiang Zhang <honzhan microsoft com>
Reviewed by: kib, mckusick
MFC after: 3 weeks
Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D8224
367 lines
10 KiB
Groff
367 lines
10 KiB
Groff
.\" Copyright (c) 2016 Microsoft Corp.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.Dd October 12, 2016
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.Dt HV_VSS 4
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.Os
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.Sh NAME
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.Nm hv_vss
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.Nd Hyper-V Volume Shadow Copy Service API
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.Sh SYNOPSIS
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.In dev/hyperv/hv_snapshot.h
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.Bd -literal
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#define VSS_SUCCESS 0x00000000
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#define VSS_FAIL 0x00000001
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enum hv_vss_op_t {
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HV_VSS_NONE = 0,
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HV_VSS_CHECK,
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HV_VSS_FREEZE,
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HV_VSS_THAW,
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HV_VSS_COUNT
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};
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struct hv_vss_opt_msg {
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uint32_t opt; /* operation */
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uint32_t status; /* 0 for success, 1 for error */
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uint64_t msgid; /* an ID used to identify the transaction */
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uint8_t reserved[48]; /* reserved values are all zeroes */
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};
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.Ed
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.Sh DESCRIPTION
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The freeze or thaw functionality of application is important to guarantee
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the application consistent backup. On windows platform, VSS is defined to do
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live backup. But for VM guest running on Hyper-V, the corresponding VSS is
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not defined yet. For example, a running database server instance, it knows when the
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applications' freeze/thaw should start or finish. But it is not aware of
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the freeze/thaw notification from Hyper-V host. The
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.Nm
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is designed to notify application freeze/thaw request.
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Thus, it plays a role of broker to forward the freeze/thaw command from Hyper-V host
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to userland application if it registered VSS service on
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.Fx
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VM, and sends the result back to Hyper-V host.
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.Pp
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Generally,
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.Xr hv_vss_daemon 8
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takes the responsiblity to freeze/thaw UFS file system,
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and it is automatically launched after system boots. When Hyper-V host wants to
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take a snapshot of the
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.Fx
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VM, it will first send VSS capability check to
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.Fx
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VM. The
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.Nm
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received the request and forward the request to userland application if it is
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registered. Only after
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.Nm
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received the VSS_SUCCESS response from application, the
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.Xr hv_vss_daemon 8
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will be informed to check whether file system freeze/thaw is supported. Any error
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occurs during this period,
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.Nm
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will inform Hyper-V host that VSS is not supported. In addition, there is a default
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timeout limit before sending response to Hyper-V host.
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If the total response time from application and
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.Xr hv_vss_daemon 8
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exceeds this value, timeout
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will occurs and VSS unsupported is responsed to Hyper-V host.
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.Pp
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After Hyper-V host confirmed the
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.Fx
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VM supports VSS, it will send freeze request to VM, and
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.Nm
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will first forward it to application. After application finished freezing, it should
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inform
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.Nm
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and file system level freezing will be triggered by
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.Xr hv_vss_daemon 8 . After all freezing
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on both application and
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.Xr hv_vss_daemon 8
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were finished, the
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.Nm
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will inform Hyper-V host that freezing is done. Of course, there is a timeout limit as
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same as VSS capability is set to make sure freezing on
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.Fx
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VM is not hang. If there is any error occurs or timeout happened, the freezing is failed
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on Hyper-V side.
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.Pp
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Hyper-V host will send thaw request after taking the snapshot, typically, this period is
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very short in order not to block the running application.
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.Nm
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firstly thaw the file system by notifying
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.Xr hv_vss_daemon 8 ,
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then notifies user registered
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application. There is also a timeout check before sending response to Hyper-V host.
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.Pp
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All the default timeout limit used in VSS capability check, freeze or thaw is the same.
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It is 15 seconds currently.
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.Sh NOTES
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.Nm
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only support UFS currently. If any of file system partition is non UFS, the VSS capability
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check will fail. If application does not register VSS,
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.Nm
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only support backup for file system level consistent. The device should be closed before it
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was opened again. If you want to simultaneously open "/dev/hv_appvss_dev" two or more times,
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an error (-1) will be returned, and errno was set.
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.Pp
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If
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.Xr hv_vss_daemon 8
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was killed after system boots, the VSS functionality will not work.
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.Sh EXAMPLES
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The following is a complete example which does nothing except for waiting 2 seconds when
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receiving those notifications from
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.Nm
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.Bd -literal
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#include <string.h>
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#include <stdio.h>
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#include <sys/ioctl.h>
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#include <sys/param.h>
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#include <sys/ucred.h>
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#include <sys/mount.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <poll.h>
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#include <stdint.h>
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#include <syslog.h>
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#include <errno.h>
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#include <err.h>
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#include <fcntl.h>
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#include <ufs/ffs/fs.h>
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#include <paths.h>
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#include <sys/ioccom.h>
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#include <dev/hyperv/hv_snapshot.h>
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#define UNDEF_FREEZE_THAW (0)
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#define FREEZE (1)
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#define THAW (2)
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#define CHECK (3)
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#define VSS_LOG(priority, format, args...) do { \\
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if (is_debugging == 1) { \\
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if (is_daemon == 1) \\
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syslog(priority, format, ## args); \\
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else \\
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printf(format, ## args); \\
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} else { \\
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if (priority < LOG_DEBUG) { \\
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if (is_daemon == 1) \\
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syslog(priority, format, ## args); \\
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else \\
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printf(format, ## args); \\
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} \\
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} \\
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} while(0)
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#define CHECK_TIMEOUT 1
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#define CHECK_FAIL 2
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#define FREEZE_TIMEOUT 1
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#define FREEZE_FAIL 2
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#define THAW_TIMEOUT 1
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#define THAW_FAIL 2
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static int is_daemon = 1;
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static int is_debugging = 0;
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static int simu_opt_waiting = 2; // seconds
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#define GENERIC_OPT(TIMEOUT, FAIL) \\
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do { \\
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sleep(simu_opt_waiting); \\
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if (opt == CHECK_TIMEOUT) { \\
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sleep(simu_opt_waiting * 10); \\
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VSS_LOG(LOG_INFO, "%s timeout simulation\\n", \\
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__func__); \\
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return (0); \\
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} else if (opt == CHECK_FAIL) { \\
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VSS_LOG(LOG_INFO, "%s failure simulation\\n", \\
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__func__); \\
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return (CHECK_FAIL); \\
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} else { \\
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VSS_LOG(LOG_INFO, "%s success simulation\\n", \\
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__func__); \\
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return (0); \\
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} \\
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} while (0)
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static int
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check(int opt)
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{
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GENERIC_OPT(CHECK_TIMEOUT, CHECK_FAIL);
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}
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static int
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freeze(int opt)
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{
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GENERIC_OPT(FREEZE_TIMEOUT, FREEZE_FAIL);
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}
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static int
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thaw(int opt)
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{
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GENERIC_OPT(THAW_TIMEOUT, THAW_FAIL);
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}
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static void usage(const char* cmd) {
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fprintf(stderr,
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"%s -f <0|1|2>: simulate app freeze."
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" 0: successful, 1: freeze timeout, 2: freeze failed\\n"
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" -c <0|1|2>: simulate vss feature check"
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" -t <0|1|2>: simulate app thaw."
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" 0: successful, 1: freeze timeout, 2: freeze failed\\n"
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" -d : enable debug mode\\n"
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" -n : run this tool under non-daemon mode\\n", cmd);
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}
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int
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main(int argc, char* argv[]) {
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int ch, freezesimuop = 0, thawsimuop = 0, checksimuop = 0, fd, r, error;
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uint32_t op;
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struct pollfd app_vss_fd[1];
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struct hv_vss_opt_msg userdata;
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while ((ch = getopt(argc, argv, "f:c:t:dnh")) != -1) {
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switch (ch) {
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case 'f':
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/* Run as regular process for debugging purpose. */
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freezesimuop = (int)strtol(optarg, NULL, 10);
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break;
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case 't':
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thawsimuop = (int)strtol(optarg, NULL, 10);
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break;
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case 'c':
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checksimuop = (int)strtol(optarg, NULL, 10);
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break;
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case 'd':
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is_debugging = 1;
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break;
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case 'n':
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is_daemon = 0;
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break;
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case 'h':
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default:
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usage(argv[0]);
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exit(0);
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}
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}
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openlog("APPVSS", 0, LOG_USER);
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/* Become daemon first. */
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if (is_daemon == 1)
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daemon(1, 0);
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else
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VSS_LOG(LOG_DEBUG, "Run as regular process.\\n");
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VSS_LOG(LOG_INFO, "HV_VSS starting; pid is: %d\\n", getpid());
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fd = open(VSS_DEV(APP_VSS_DEV_NAME), O_RDWR);
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if (fd < 0) {
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VSS_LOG(LOG_ERR, "Fail to open %s, error: %d %s\\n",
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VSS_DEV(APP_VSS_DEV_NAME), errno, strerror(errno));
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exit(EXIT_FAILURE);
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}
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app_vss_fd[0].fd = fd;
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app_vss_fd[0].events = POLLIN | POLLRDNORM;
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while (1) {
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r = poll(app_vss_fd, 1, INFTIM);
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VSS_LOG(LOG_DEBUG, "poll returned r = %d, revent = 0x%x\\n",
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r, app_vss_fd[0].revents);
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if (r == 0 || (r < 0 && errno == EAGAIN) ||
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(r < 0 && errno == EINTR)) {
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/* Nothing to read */
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continue;
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}
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if (r < 0) {
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/*
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* For poll return failure other than EAGAIN,
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* we want to exit.
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*/
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VSS_LOG(LOG_ERR, "Poll failed.\\n");
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perror("poll");
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exit(EIO);
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}
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/* Read from character device */
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error = ioctl(fd, IOCHVVSSREAD, &userdata);
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if (error < 0) {
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VSS_LOG(LOG_ERR, "Read failed.\\n");
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perror("pread");
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exit(EIO);
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}
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if (userdata.status != 0) {
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VSS_LOG(LOG_ERR, "data read error\\n");
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continue;
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}
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op = userdata.opt;
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switch (op) {
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case HV_VSS_CHECK:
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error = check(checksimuop);
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break;
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case HV_VSS_FREEZE:
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error = freeze(freezesimuop);
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break;
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case HV_VSS_THAW:
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error = thaw(thawsimuop);
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break;
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default:
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VSS_LOG(LOG_ERR, "Illegal operation: %d\\n", op);
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error = VSS_FAIL;
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}
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if (error)
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userdata.status = VSS_FAIL;
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else
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userdata.status = VSS_SUCCESS;
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error = ioctl(fd, IOCHVVSSWRITE, &userdata);
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if (error != 0) {
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VSS_LOG(LOG_ERR, "Fail to write to device\\n");
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exit(EXIT_FAILURE);
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} else {
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VSS_LOG(LOG_INFO, "Send response %d for %s to kernel\\n",
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userdata.status, op == HV_VSS_FREEZE ? "Freeze" :
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(op == HV_VSS_THAW ? "Thaw" : "Check"));
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}
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}
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return 0;
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}
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.Sh SEE ALSO
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.Xr hv_vss_daemon 8 ,
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.Xr hv_utils 4
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.Sh HISTORY
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The daemon was introduced in October 2016 and developed by Microsoft Corp.
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.Sh AUTHORS
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.An -nosplit
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.Fx
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support for
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.Nm
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was first added by
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.An Microsoft BSD Integration Services Team Aq Mt bsdic@microsoft.com .
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