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Re: [Libguestfs] [PATCH 00/10] virt-resize: add support for resizing MBR logical partitions



On 04/30/2015 06:51 PM, Chen, Hanxiao wrote:
> Hi, Rich
>
>> -----Original Message-----
>> From: Richard W.M. Jones [mailto:rjones redhat com]
>> Sent: Wednesday, April 29, 2015 7:04 PM
>> To: Chen, Hanxiao/陈 晗霄
>> Cc: libguestfs redhat com
>> Subject: Re: [Libguestfs] [PATCH 00/10] virt-resize: add support for resizing MBR
>> logical partitions
>>
>> On Wed, Apr 29, 2015 at 09:19:24AM +0000, Chen, Hanxiao wrote:
>>> commit 6e989fd709fea37430398cbb7c01c52cd44bd1ac already did this:
>>> we had p_mbr_p_type : partition_type in type partition.
>>> Like what MBR/EBR did, this patchset use `partition_type`:
>>>
>>> /dev/sda3:
>>> 	partition data: 3 210763776-420478975 (209715200 bytes)
>>> 	bootable: false
>>> 	partition ID: 0x5
>>> 	content: extended partition
>>> 	label: (none)
>>> 	GUID: (none)
>>> 	*partition type: extended*
>>> /dev/sda5:
>>> 	partition data: 5 211812352-222298111 (10485760 bytes)
>>> 	bootable: false
>>> 	partition ID: 0x83
>>> 	content: unknown data
>>> 	label: (none)
>>> 	GUID: (none)
>>> 	*partition type: logical*
>>>
>>> As we could only had one extended partition,
>>> all logical partitions belong to that extended partition,
>>> so current type partition of virt-resize can reflect logical/extended partition
>> model.
>>
>> The specific problem is that the extended partition (eg /dev/sda3)
>> contains the logical partition (/dev/sda5).  Having a flat list
>> doesn't express that at all.
> We had at most 4 PTE in MBR, in PTE, a partition type is on +04h, 
> value 05h or 0fh shows it's an extended partition.
> From extended partition's EBR, we got logical partitions.
>
> sda1-- sda2 -- sda3 -- sda4
>                    ^
>                    |
>                   sda5 -- sda6
>
> I think we do not need to show this specially,
> just use the original design:
> logical partitions existed in extended partition, an implicit relations.
>
> So a flat list can do this:
> We mark each members, then a tree view above could be rebuilt precisely
> from plat list.
Hi, Rich

Any comments on this?

Regards,
- Chen
>
>
> In this patchset, logical partitions are not filter out, it did:
>
> 1) partitions list: sda1 sda2 sda3 sda5
> every member of partitions got a member `partition type`
>
> 2) calculate surplus
>
> 3) then filter out logical partitions list:
> logical_partitions: sda5
> partitions: sda1 sda2 sda3
> do something to it (calculate_target_partitions...)
>
> 4) part_add to 'non-logical' partitions and logical partitions,
> then concrete them together for the original partition list.
>
> 5) copy_partition (ignore extended partitions, for we had logical partition
> in partitions list, we copy data from there)
>
>> I agree it is very hard to express this, because extended partitions
>> just work so differently from how any sensible partition scheme should
>> work (because they are a big hack).  But perhaps:
>>
>>  - flat list of primary partitions (as now, the global 'partitions')
> members of partitions list whose partition type is 'primary'
>>  - one MBR extended partition (as a new global variable)
> member of partitions list whose partition type is 'extended'.
>
>>  - flat list of logical partitions
> members of partitions list whose partition type is 'logical'.
>
> So I think we do not need 2 list and a global variable,
> if we want to know something, just do a List.filter.
>
>> would do it?  It still has the problem that the extended partition is
>> a bit like a primary partition, yet isn't in the partitions list.
> For the point of PTE's view, it does.
> PS: In my patch, it's in partitions list :)
>
> Regards
> - Chen
>
>>>> It's very hard to understand what changes are being made.  The commits
>>>> are not grouped in a way that makes them easily understandable to me.
>>> I'll try to regroup them and make the patchset easy to review.
>> Thanks,
>>
>> Rich.
>>
>> --
>> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
>> Read my programming and virtualization blog: http://rwmj.wordpress.com
>> virt-p2v converts physical machines to virtual machines.  Boot with a
>> live CD or over the network (PXE) and turn machines into KVM guests.
>> http://libguestfs.org/virt-v2v



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