guest-fsfreeze-freeze freezes all mounted block devices

[Marc Roos]

Hmmm, using 'virsh domfsinfo testdom' gives me a crash in win2008r2 
(using software from virtio-win-0.1.171.iso)

Fault bucket , type 0
Event Name: APPCRASH
Response: Not available
Cab Id: 0

Problem signature:
P1: qemu-ga.exe
P2: 100.0.0.0
P3: 5c473543
P4: KERNELBASE.dll
P5: 6.1.7601.24545
P6: 5e0eb6bd
P7: c0000005
P8: 000000000000c4d2
P9: 
P10: 

Attached files:

These files may be available here:
C:\ProgramData\Microsoft\Windows\WER\ReportQueue\AppCrash_qemu-ga.exe_bd
2e6535bdb93328680e0285e89e08f2866db83_0b0deada

Analysis symbol: 
Rechecking for solution: 0
Report Id: 3d82596e-517c-11ea-b213-525400e83365
Report Status: 0


-----Original Message-----
Cc: libvirt-users
Subject: Re: guest-fsfreeze-freeze freezes all mounted block devices

On Mon, Feb 17, 2020 at 10:03:27 +0100, Marc Roos wrote:
> Hi Peter,
> 
> Should I assume that the virsh domfsfreeze, does not require the 
> qemu-agent service in the guest?

No. That's the official way how to drive the "guest-fsfreeze-freeze"
agent command via libvirt, thus you must have the guest agent the same 
way as you used it before.

Using qemu-agent-command is a backdoor for testing arbitrary commands 
and thus you can break things. You are on your own if stuff breaks using 
that approach.

> PS. I couldn't find the result. Afaik it looks like it is returning 
> the amount of frozen/thawed filesystem's

qemu.git/gqa/qapi-schema.json says:

##
# @guest-fsfreeze-freeze:
#
# Sync and freeze all freezable, local guest filesystems. If this # 
command succeeded, you may call @guest-fsfreeze-thaw later to # 
unfreeze.
#
# Note: On Windows, the command is implemented with the help of a # 
Volume Shadow-copy Service DLL helper. The frozen state is limited # for 
up to 10 seconds by VSS.
#
# Returns: Number of file systems currently frozen. On error, all 
filesystems # will be thawed. If no filesystems are frozen as a result 
of this call, # then @guest-fsfreeze-status will remain "thawed" and 
calling # @guest-fsfreeze-thaw is not necessary.
#
# Since: 0.15.0

You might also want to have a look at 'guest-fsfreeze-freeze-list'.


> 
> -----Original Message-----
> Cc: libvirt-users
> Subject: Re: guest-fsfreeze-freeze freezes all mounted block devices
> 
> On Fri, Feb 14, 2020 at 22:14:55 +0100, Marc Roos wrote:
> > 
> > I wondered if anyone here can confirm that
> > 
> > virsh qemu-agent-command domain 
'{"execute":"guest-fsfreeze-freeze"}'
> 
> Note that libvirt implements this directly via 'virsh domfsfreeze'. 
> This is the corresponding man page entry:
> 
>   domfsfreeze domain [[--mountpoint] mountpoint...]
>       Freeze mounted filesystems within a running domain to prepare 
> for consistent snapshots.
> 
>       The --mountpoint option takes a parameter mountpoint, which is a 

> mount point path of the filesystem to be frozen.
>       This option can occur multiple times. If this is not specified, 
> every mounted filesystem is frozen.
> 
> 
> > Freezes all mounted block devices filesystems. So if I use 4 block 
> > devices they are all frozen for snapshotting. Or just the root fs?

As a side note. For snapshotting via virsh snapshot-create use the 
--quiesce option which does what you want or the virsh command with 
arguments if you don't want to freeze everything.

> 
> Since you are using agent passthrough where libvirt doesn't do any 
> interpretation of what happens please refer to the appropriate QEMU 
> agent documentation for the semantics of the command you've used.
> 
> 
>