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Re: [Libguestfs] New tool proposal



On 05/22/2012 08:15 PM, Richard W.M. Jones wrote:

> On Tue, May 22, 2012 at 08:01:50PM +0800, Wanlong Gao wrote:
>> So, you means we can use virt-ls to list the different files list, and then
>> use virt-cat to see the different between two single files?
> 
> Yes, this is what I usually do.
> 
> For example:
> 
>   $ qemu-img create -f qcow2 -b /dev/vg_pin/F16x64 cloned-f16.img
>   Formatting 'cloned-f16.img', fmt=qcow2 size=21474836480 backing_file='/dev/vg_pin/F16x64' encryption=off cluster_size=65536 
>   
>   $ qemu-kvm -hda cloned-f16.img -m 1024
>   [boot it, shut it down]
>   
>   $ virt-ls -lR -a /dev/vg_pin/F16x64 / > original.files     # *
>   $ virt-ls -lR -a cloned-f16.img / > modified.files
>   
>   $ diff -u original.files modified.files
>   --- original.files      2012-05-22 13:11:00.949456251 +0100
>   +++ modified.files      2012-05-22 13:11:38.248133406 +0100
>   @@ -1651,7 +1651,7 @@
>    - 0644        373 /etc/rearj.cfg
>    l 0777         14 /etc/redhat-release -> fedora-release
>    - 0644       1787 /etc/request-key.conf
>   -- 0644         79 /etc/resolv.conf
>   +- 0644         74 /etc/resolv.conf
>    l 0777         11 /etc/rmt -> ../sbin/rmt
>    - 0644       1615 /etc/rpc
>    d 0755       4096 /etc/rpm
>   @@ -32090,6 +32090,7 @@
>    d 0775       4096 /sys
>    d 1777       4096 /tmp
>    d 1777       4096 /tmp/.ICE-unix
>   +s 0777          0 /tmp/.ICE-unix/1061
>    s 0777          0 /tmp/.ICE-unix/1085
>    d 1777       4096 /tmp/.Test-unix
>    d 1777       4096 /tmp/.X11-unix
>   @@ -207760,7 +207761,7 @@
>    - 0644         28 /var/lib/AccountsService/users/rjones
>    d 0755       4096 /var/lib/NetworkManager
>    - 0644         87 /var/lib/NetworkManager/NetworkManager.state
>   -- 0644       1454 /var/lib/NetworkManager/timestamps
>   +- 0644       1502 /var/lib/NetworkManager/timestamps
>    d 0755       4096 /var/lib/PackageKit
>    - 0644       9216 /var/lib/PackageKit/transactions.db
>    d 0755       4096 /var/lib/alsa
>   
>   [etc etc]
> 
> However there are some shortcomings.  It won't find differences in:
> 
> - filesystem metadata
> - bootloaders or other information outside the regular filesystem
> - inside the Windows Registry (it'll just say the two binary
>   blobs are different)
> 
> Rich.
> 
> * You don't need the --checksum option unless files are modified but
>   keep the same size, in which case you have to examine the complete
>   content of each file.  Using --checksum is much slower.  'virt-ls'
>   has other options that you may want to look at.
> 


Hi Rich,

Kame gave me a very good detail about the use case of virt-diff example, now
quoted them for you,

> Anyway, in above scheme, we cannot compare the files of the same size.
> For example
> 
> In guest 01:
> # cat /etc/sysconfig/network
> NETWORKING=yes
> HOSTNAME=guest01
> GATEWAY=10.124.196.1
> 
> In guest02:
> # cat /etc/sysconfig/network
> NETWORKING=yes
> HOSTNAME=guest02
> GATEWAY=10.124.196.1
> 
> 
> You need to diff even if you have file lists.
> 
> BTW, what we'd like to compare is the contents of file, not meta-data.
> 
> In another point of view....
> 
> In your example in mailing list, you compares 2 files.
> 
> But, now, I _think_ what users really want is a command like following.
> 
> Following command is comparing guest's file of Guest01...Guest04 with Guest00.
> 
> # virt-diff -seed Guest00 -name Guest01 -name Guest02 -name Guest03 -name Guest04 /etc/hogehoge
> Guest03:/etc/hogehoge is differ.
> diff result...
> 
> In this case, only Guest03 has a different contents of the file.
> 
> For system-admin, this means...
> - Guest00,01,02,04 are correct and 03 is wrong
> or
> - Guest03 is correct and Guest00,01,02,04 are wrong.
> or
> - Guest03 has different settings intentionally and he confirmed that.
> 
> This command will be very good for system-admin.

Then, any thoughts about this tool ?
and more thoughts about implementing this ?
We should implement a "diff" wrapper in the guestfsd, and use this API when
implementing this tool or any other methods?


Thanks,
Wanlong Gao


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