Re: [Qemu-devel] qcow2 resize with snapshots

[Kevin Wolf]

Am 16.05.2016 um 08:33 hat zhangzhiming geschrieben:
> hi,  i read some source code by your tips, and i have some conclusions:
> 
> 1. Old version of QCOW2 image does not store the total size of snapshot, so, 
> we
> can’t 
> add the function to the old version of QEMU, and the function of QCOW2
> resize with snapshots 
> will be limited in V3 image or it will make confusion. so that is right.
> 2. I read the source code of bdrv_truncate from master, and the function
> “bdrv_dirty_bitmap_truncate" have done this, so 
> it means that i need not to consider the resize of bitmap while resize
> QCOW2 ?

This is correct, qcow2_truncate() does not need to consider it.

However, snapshot loading must consider it. Essentially, when allowing
snapshots with different image sizes, qcow2_snapshot_goto() is an
implicit resize as well, even though it doesn't go through
bdrv_truncate().

> 3. there is a function named “qmp_marshal_block_resize”, 
> this function will block IO requests when resizing a image, and it seems
> that it called callback function to notify the 
> guest, and we don’t need to set BLOCK_OP_TYPE_RESIZE blockers. is it
> correct ?

I think you mean qmp_block_resize(). (This is the function that is
called by the automatically generated qmp_marshal_block_resize().)

For the same reason as above (snapshot loading = implicit resize), we
need to check the blocker and call the callbacks for snapshot loading
now.

Kevin

> On May 7, 2016, at 11:13 AM, zhangzhiming 
> wrote:
> 
> sorry, i forgot to cc qemu-bl...@nongnu.org.
> 
> zhangzhiming
> zhangzhimin...@meituan.com
> 
> 
> 
> 
> On May 7, 2016, at 10:47 AM, zhangzhiming 
> wrote:
> 
> thank you for your reply, and i am glad to join to the development of
> qemu.
> i will try my best to finish this new function.
> 
> have a good day!
> 
> zhangzhiming
> zhangzhimin...@meituan.com
> 
> 
> 
> 
> On May 3, 2016, at 4:44 PM, Kevin Wolf  wrote:
> 
> [ Cc: qemu-block ]
> 
> Am 29.04.2016 um 10:59 hat zhangzm geschrieben:
> 
> hi, i want to implement the function of qcow2 resize which has
> snapshots.
> 
> each snapshot of qcow2 will have a separate total size, and
> when apply
> a snapshot, the image can be shrunk, and the total size of
> image will
> change after apply to a snapshot with different size.
> 
> now, there is a disk_size value in struct QcowSnapshot, i only
> need to
> change the size of current active image layer when apply a
> snapshot
> with different size, and the io request will be limit in the
> range of
> active layer.
> 
> 
> Yes, I think today the qcow2 format provides everything that is
> needed
> to implement this. You need to make sure that we have a v3 image 
> so
> that
> the virtual disk size is actually stored in the snapshot (this
> field did
> not exist in v2 images yet).
> 
> What you need to consider is that loading a snapshot becomes
> similar to
> resizing an image then and you need to do the same things for it.
> For
> example, we need to figure out what to do with associated dirty
> bitmaps
> (adapt them to the new size like in bdrv_truncate()?), call resize
> callbacks so that the guest devices actually see the changes size
> and
> possibly also consider the BLOCK_OP_TYPE_RESIZE blockers to 
> prevent
> a
> size change while the image is in use.
> 
> 
> and i want my code merged into the master of qemu.
> 
> 
> The wiki has a few tips on how to submit patches for qemu:
> http://wiki.qemu.org/Contribute/SubmitAPatch
> 
> For a patch (or patch series) like this, you will want to CC at
> least
> qemu-block and qemu-devel, plus possibly a few individual people.
> 
> Kevin
> 
> 
> 
> 
> 
> 
> 
> 

Re: [Qemu-devel] qcow2 resize with snapshots

[zhangzhiming]

hi,  i read some source code by your tips, and i have some conclusions:

1. Old version of QCOW2 image does not store the total size of snapshot, so, we 
can’t 
add the function to the old version of QEMU, and the function of QCOW2 
resize with snapshots 
will be limited in V3 image or it will make confusion. so that is right.
2. I read the source code of bdrv_truncate from master, and the function 
“bdrv_dirty_bitmap_truncate" have done this, so 
it means that i need not to consider the resize of bitmap while resize 
QCOW2 ?
3. there is a function named “qmp_marshal_block_resize”, 
this function will block IO requests when resizing a image, and it seems 
that it called callback function to notify the 
guest, and we don’t need to set BLOCK_OP_TYPE_RESIZE blockers. is it 
correct ?


zhangzhiming
zhangzhimin...@meituan.com



> On May 7, 2016, at 11:13 AM, zhangzhiming  wrote:
> 
> sorry, i forgot to cc qemu-bl...@nongnu.org .
> 
> zhangzhiming
> zhangzhimin...@meituan.com 
> 
> 
> 
>> On May 7, 2016, at 10:47 AM, zhangzhiming > > wrote:
>> 
>> thank you for your reply, and i am glad to join to the development of qemu.
>> i will try my best to finish this new function.
>> 
>> have a good day!
>> 
>> zhangzhiming
>> zhangzhimin...@meituan.com 
>> 
>> 
>> 
>>> On May 3, 2016, at 4:44 PM, Kevin Wolf  wrote:
>>> 
>>> [ Cc: qemu-block ]
>>> 
>>> Am 29.04.2016 um 10:59 hat zhangzm geschrieben:
 hi, i want to implement the function of qcow2 resize which has
 snapshots.
 
 each snapshot of qcow2 will have a separate total size, and when apply
 a snapshot, the image can be shrunk, and the total size of image will
 change after apply to a snapshot with different size.
 
 now, there is a disk_size value in struct QcowSnapshot, i only need to
 change the size of current active image layer when apply a snapshot
 with different size, and the io request will be limit in the range of
 active layer.
>>> 
>>> Yes, I think today the qcow2 format provides everything that is needed
>>> to implement this. You need to make sure that we have a v3 image so that
>>> the virtual disk size is actually stored in the snapshot (this field did
>>> not exist in v2 images yet).
>>> 
>>> What you need to consider is that loading a snapshot becomes similar to
>>> resizing an image then and you need to do the same things for it. For
>>> example, we need to figure out what to do with associated dirty bitmaps
>>> (adapt them to the new size like in bdrv_truncate()?), call resize
>>> callbacks so that the guest devices actually see the changes size and
>>> possibly also consider the BLOCK_OP_TYPE_RESIZE blockers to prevent a
>>> size change while the image is in use.
>>> 
 and i want my code merged into the master of qemu.
>>> 
>>> The wiki has a few tips on how to submit patches for qemu:
>>> http://wiki.qemu.org/Contribute/SubmitAPatch
>>> 
>>> For a patch (or patch series) like this, you will want to CC at least
>>> qemu-block and qemu-devel, plus possibly a few individual people.
>>> 
>>> Kevin
>>> 
>> 
>> 
> 

Re: [Qemu-devel] qcow2 resize with snapshots

[zhangzhiming]

sorry, i forgot to cc qemu-bl...@nongnu.org .

zhangzhiming
zhangzhimin...@meituan.com



> On May 7, 2016, at 10:47 AM, zhangzhiming  wrote:
> 
> thank you for your reply, and i am glad to join to the development of qemu.
> i will try my best to finish this new function.
> 
> have a good day!
> 
> zhangzhiming
> zhangzhimin...@meituan.com
> 
> 
> 
>> On May 3, 2016, at 4:44 PM, Kevin Wolf  wrote:
>> 
>> [ Cc: qemu-block ]
>> 
>> Am 29.04.2016 um 10:59 hat zhangzm geschrieben:
>>> hi, i want to implement the function of qcow2 resize which has
>>> snapshots.
>>> 
>>> each snapshot of qcow2 will have a separate total size, and when apply
>>> a snapshot, the image can be shrunk, and the total size of image will
>>> change after apply to a snapshot with different size.
>>> 
>>> now, there is a disk_size value in struct QcowSnapshot, i only need to
>>> change the size of current active image layer when apply a snapshot
>>> with different size, and the io request will be limit in the range of
>>> active layer.
>> 
>> Yes, I think today the qcow2 format provides everything that is needed
>> to implement this. You need to make sure that we have a v3 image so that
>> the virtual disk size is actually stored in the snapshot (this field did
>> not exist in v2 images yet).
>> 
>> What you need to consider is that loading a snapshot becomes similar to
>> resizing an image then and you need to do the same things for it. For
>> example, we need to figure out what to do with associated dirty bitmaps
>> (adapt them to the new size like in bdrv_truncate()?), call resize
>> callbacks so that the guest devices actually see the changes size and
>> possibly also consider the BLOCK_OP_TYPE_RESIZE blockers to prevent a
>> size change while the image is in use.
>> 
>>> and i want my code merged into the master of qemu.
>> 
>> The wiki has a few tips on how to submit patches for qemu:
>> http://wiki.qemu.org/Contribute/SubmitAPatch
>> 
>> For a patch (or patch series) like this, you will want to CC at least
>> qemu-block and qemu-devel, plus possibly a few individual people.
>> 
>> Kevin
>> 
> 
> 

Re: [Qemu-devel] qcow2 resize with snapshots

[zhangzhiming]

thank you for your reply, and i am so sorry, there are some problems with my 
email @163.com , 
it returned me some error and i thought that my email send failed.
so, really sorry. this is my second email. i will use this one.

zhangzhiming
zhangzhimin...@meituan.com



> On May 6, 2016, at 7:20 PM, Kevin Wolf  wrote:
> 
> Am 06.05.2016 um 07:57 hat zhangzhiming geschrieben:
>> hi, i want to implement the function of qcow2 resize which has snapshots.
>> each snapshot of qcow2 will have a separate total size, and when apply a 
>> snapshot,
>> the image can be shrunk, and the total size of image will change after apply 
>> to a snapshot 
>> with different size.
>> now, there is a disk_size value in struct QcowSnapshot, i only need to 
>> change the size of current active 
>> image layer when apply a snapshot with different size, and the io request 
>> will be limit in the range of active layer.
>> 
>> and i want my code merged into the master of qemu.
>> please give me some comments. thanks.
> 
> You asked the same a week ago, and I replied you there:
> 
> https://lists.gnu.org/archive/html/qemu-devel/2016-05/msg00178.html
> 
> In order to keep meaningful email threading, please reply to that mail
> if you need more information.
> 
> Kevin
> 

Re: [Qemu-devel] qcow2 resize with snapshots

[zhangzhiming]

thank you for your reply, and i am glad to join to the development of qemu.
i will try my best to finish this new function.

have a good day!

zhangzhiming
zhangzhimin...@meituan.com



> On May 3, 2016, at 4:44 PM, Kevin Wolf  wrote:
> 
> [ Cc: qemu-block ]
> 
> Am 29.04.2016 um 10:59 hat zhangzm geschrieben:
>> hi, i want to implement the function of qcow2 resize which has
>> snapshots.
>> 
>> each snapshot of qcow2 will have a separate total size, and when apply
>> a snapshot, the image can be shrunk, and the total size of image will
>> change after apply to a snapshot with different size.
>> 
>> now, there is a disk_size value in struct QcowSnapshot, i only need to
>> change the size of current active image layer when apply a snapshot
>> with different size, and the io request will be limit in the range of
>> active layer.
> 
> Yes, I think today the qcow2 format provides everything that is needed
> to implement this. You need to make sure that we have a v3 image so that
> the virtual disk size is actually stored in the snapshot (this field did
> not exist in v2 images yet).
> 
> What you need to consider is that loading a snapshot becomes similar to
> resizing an image then and you need to do the same things for it. For
> example, we need to figure out what to do with associated dirty bitmaps
> (adapt them to the new size like in bdrv_truncate()?), call resize
> callbacks so that the guest devices actually see the changes size and
> possibly also consider the BLOCK_OP_TYPE_RESIZE blockers to prevent a
> size change while the image is in use.
> 
>> and i want my code merged into the master of qemu.
> 
> The wiki has a few tips on how to submit patches for qemu:
> http://wiki.qemu.org/Contribute/SubmitAPatch
> 
> For a patch (or patch series) like this, you will want to CC at least
> qemu-block and qemu-devel, plus possibly a few individual people.
> 
> Kevin
> 

Re: [Qemu-devel] qcow2 resize with snapshots

[Kevin Wolf]

Am 06.05.2016 um 07:57 hat zhangzhiming geschrieben:
> hi, i want to implement the function of qcow2 resize which has snapshots.
> each snapshot of qcow2 will have a separate total size, and when apply a 
> snapshot,
> the image can be shrunk, and the total size of image will change after apply 
> to a snapshot 
> with different size.
> now, there is a disk_size value in struct QcowSnapshot, i only need to change 
> the size of current active 
> image layer when apply a snapshot with different size, and the io request 
> will be limit in the range of active layer.
> 
> and i want my code merged into the master of qemu.
> please give me some comments. thanks.

You asked the same a week ago, and I replied you there:

https://lists.gnu.org/archive/html/qemu-devel/2016-05/msg00178.html

In order to keep meaningful email threading, please reply to that mail
if you need more information.

Kevin

[Qemu-devel] qcow2 resize with snapshots

[zhangzhiming]

hi, i want to implement the function of qcow2 resize which has snapshots.
each snapshot of qcow2 will have a separate total size, and when apply a 
snapshot,
the image can be shrunk, and the total size of image will change after apply to 
a snapshot 
with different size.
now, there is a disk_size value in struct QcowSnapshot, i only need to change 
the size of current active 
image layer when apply a snapshot with different size, and the io request will 
be limit in the range of active layer.

and i want my code merged into the master of qemu.
please give me some comments. thanks.


zhangzhiming
zhangzhimin...@meituan.com

Re: [Qemu-devel] qcow2 resize with snapshots

[Kevin Wolf]

[ Cc: qemu-block ]

Am 29.04.2016 um 10:59 hat zhangzm geschrieben:
> hi, i want to implement the function of qcow2 resize which has
> snapshots.
>
> each snapshot of qcow2 will have a separate total size, and when apply
> a snapshot, the image can be shrunk, and the total size of image will
> change after apply to a snapshot with different size.
>
> now, there is a disk_size value in struct QcowSnapshot, i only need to
> change the size of current active image layer when apply a snapshot
> with different size, and the io request will be limit in the range of
> active layer.

Yes, I think today the qcow2 format provides everything that is needed
to implement this. You need to make sure that we have a v3 image so that
the virtual disk size is actually stored in the snapshot (this field did
not exist in v2 images yet).

What you need to consider is that loading a snapshot becomes similar to
resizing an image then and you need to do the same things for it. For
example, we need to figure out what to do with associated dirty bitmaps
(adapt them to the new size like in bdrv_truncate()?), call resize
callbacks so that the guest devices actually see the changes size and
possibly also consider the BLOCK_OP_TYPE_RESIZE blockers to prevent a
size change while the image is in use.

> and i want my code merged into the master of qemu.

The wiki has a few tips on how to submit patches for qemu:
http://wiki.qemu.org/Contribute/SubmitAPatch

For a patch (or patch series) like this, you will want to CC at least
qemu-block and qemu-devel, plus possibly a few individual people.

Kevin

[Qemu-devel] qcow2 resize with snapshots

[zhangzm]

hi, i want to implement the function of qcow2 resize which has snapshots.

each snapshot of qcow2 will have a separate total size, and when apply a 
snapshot,

the image can be shrunk, and the total size of image will change after apply to 
a snapshot 

with different size.

now, there is a disk_size value in struct QcowSnapshot, i only need to change 
the size of current active 

image layer when apply a snapshot with different size, and the io request will 
be limit in the range of active layer.




and i want my code merged into the master of qemu.

please give me some comments. thanks.



zhangzhiming

zhangzhiming...@163.com

[Qemu-devel] qcow2 resize with snapshots

[zhangzm]

hi, i want to implement the function of qcow2 resize which has snapshots.

each snapshot of qcow2 will have a separate total size, and when apply a 
snapshot,

the image can be shrunk, and the total size of image will change after apply to 
a snapshot 

with different size.

now, there is a disk_size value in struct QcowSnapshot, i only need to change 
the size of current active 

image layer when apply a snapshot with different size, and the io request will 
be limit in the range of active layer.




and i want my code merged into the master of qemu.

please give me some comments. thanks.



zhangzhiming

zhangzhiming...@163.com