Re: [Xen-devel] inconsistent metadata of vhd file while live migration

[Daniel Stodden <daniel.stodden@xxxxxxxxxx>]

On Wed, 2011-02-16 at 05:55 -0500, alice wan wrote:
> option b, c seems simpler and needs less codes for my code
> version(xen4.0.0+2.6.31.13).

Example:

[1]+ tail -f /var/log/daemon.log &

root@vantst07:~# tap-ctl list
    7781  0    0        vhd /var/tmp/lenny.vhd
Feb 16 13:04:00 vantst07 tapdisk2[7779]: received 'pid' message (uuid = 0)
Feb 16 13:04:00 vantst07 tapdisk2[7779]: sending 'pid response' message (uuid = 
0)
Feb 16 13:04:00 vantst07 tapdisk2[7779]: received 'list' message (uuid = 65535)
Feb 16 13:04:00 vantst07 tapdisk2[7779]: sending 'list response' message (uuid 
= 65535)
Feb 16 13:04:00 vantst07 tapdisk2[7779]: sending 'list response' message (uuid 
= 65535)

root@vantst07:~# tap-ctl pause -p 7781 -m 0
Feb 16 13:04:12 vantst07 tapdisk2[7779]: received 'pause' message (uuid = 0)
Feb 16 13:04:12 vantst07 tapdisk2[7779]: /var/tmp/lenny.vhd: b: 256, a: 256, f: 
140, n: 1050624
Feb 16 13:04:12 vantst07 tapdisk2[7779]: closed image /var/tmp/lenny.vhd (0 
users, state: 0x00000000, type: 4)
Feb 16 13:04:12 vantst07 tapdisk2[7779]: sending 'pause response' message (uuid 
= 0)

root@vantst07:~# tap-ctl unpause -p 7781 -m 0
Feb 16 13:04:20 vantst07 tapdisk2[7779]: received 'resume' message (uuid = 0)
Feb 16 13:04:20 vantst07 tapdisk2[7779]: /var/tmp/lenny.vhd version: tap 
0x00010003, b: 256, a: 256, f: 140, n: 1050624
Feb 16 13:04:20 vantst07 tapdisk2[7779]: opened image /var/tmp/lenny.vhd (1 
users, state: 0x00000001, type: 4)
Feb 16 13:04:20 vantst07 tapdisk2[7779]: VBD CHAIN:
Feb 16 13:04:20 vantst07 tapdisk2[7779]: /var/tmp/lenny.vhd: 4
Feb 16 13:04:20 vantst07 tapdisk2[7779]: sending 'resume response' message 
(uuid = 0)

> i'm not familiar with blktap code. would you please tell in which
> function blktap run an implicit close/open when process first io?

I think those lines never made it into tools/blktap. XCP's srpm should
still have those patches, but they're already removed post-5.6fp1, so
I'd recommend to rather go for b. and let c. fade out. The toolstack
should stay in control, not the disk to try paper over mistaken
assumptions.

> and in latest stable version blktap2 pause/unpause is available ?

Yup.

Daniel

> thanks
> 2011/2/14 Daniel Stodden <daniel.stodden@xxxxxxxxxx>
>         On Sun, 2011-02-13 at 16:11 -0500, Daniel Stodden wrote:
>         
>         > B. Hack.
>         >    Let the toolstack issue a tap-ctl pause/unpause cycle
>         before resume.
>         >    This will reopen the image.
>         >
>         > C. Back then, in the dark ages, blktap did this implicitly.
>         >    Every
>         
>         
>          *first*
>         
>         >  I/O request after disk create run an implicit close/open
>         
>         >    cycle.
>         
>         :o)
>         
>         D
>         a
>         niel
>         
>         
>         
> 



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