[PATCH] qapi: deprecate drive-backup

Vladimir Sementsov-Ogievskiy posted 1 patch 2 weeks, 1 day ago
Failed in applying to current master (apply log)
docs/system/deprecated.rst | 5 +++++
qapi/block-core.json       | 5 ++++-
2 files changed, 9 insertions(+), 1 deletion(-)

[PATCH] qapi: deprecate drive-backup

Posted by Vladimir Sementsov-Ogievskiy 2 weeks, 1 day ago
Modern way is using blockdev-add + blockdev-backup, which provides a
lot more control on how target is opened.

As example of drive-backup problems consider the following:

User of drive-backup expects that target will be opened in the same
cache and aio mode as source. Corresponding logic is in
drive_backup_prepare(), where we take bs->open_flags of source.

It works rather bad if source was added by blockdev-add. Assume source
is qcow2 image. On blockdev-add we should specify aio and cache options
for file child of qcow2 node. What happens next:

drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is
places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
as file-posix parse options and simply set s->use_linux_aio.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---

Hi all! I remember, I suggested to deprecate drive-backup some time ago,
and nobody complain.. But that old patch was inside the series with
other more questionable deprecations and it did not landed.

Let's finally deprecate what should be deprecated long ago.

We now faced a problem in our downstream, described in commit message.
In downstream I've fixed it by simply enabling O_DIRECT and linux_aio
unconditionally for drive_backup target. But actually this just shows
that using drive-backup in blockdev era is a bad idea. So let's motivate
everyone (including Virtuozzo of course) to move to new interfaces and
avoid problems with all that outdated option inheritance.

 docs/system/deprecated.rst | 5 +++++
 qapi/block-core.json       | 5 ++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
index 80cae86252..b6f5766e17 100644
--- a/docs/system/deprecated.rst
+++ b/docs/system/deprecated.rst
@@ -186,6 +186,11 @@ Use the more generic commands ``block-export-add`` and ``block-export-del``
 instead.  As part of this deprecation, where ``nbd-server-add`` used a
 single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
 
+``drive-backup`` (since 6.0)
+''''''''''''''''''''''''''''
+
+Use ``blockdev-backup`` in pair with ``blockdev-add`` instead.
+
 System accelerators
 -------------------
 
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 6d227924d0..8e2c6e1622 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1642,6 +1642,9 @@
 # The operation can be stopped before it has completed using the
 # block-job-cancel command.
 #
+# Features:
+# @deprecated: This command is deprecated. Use @blockdev-backup instead.
+#
 # Returns: - nothing on success
 #          - If @device is not a valid block device, GenericError
 #
@@ -1657,7 +1660,7 @@
 #
 ##
 { 'command': 'drive-backup', 'boxed': true,
-  'data': 'DriveBackup' }
+  'data': 'DriveBackup', 'features': ['deprecated'] }
 
 ##
 # @blockdev-backup:
-- 
2.29.2


Re: [PATCH] qapi: deprecate drive-backup

Posted by John Snow 1 week, 5 days ago
On 4/23/21 8:59 AM, Vladimir Sementsov-Ogievskiy wrote:
> Modern way is using blockdev-add + blockdev-backup, which provides a
> lot more control on how target is opened.
> 
> As example of drive-backup problems consider the following:
> 
> User of drive-backup expects that target will be opened in the same
> cache and aio mode as source. Corresponding logic is in
> drive_backup_prepare(), where we take bs->open_flags of source.
> 
> It works rather bad if source was added by blockdev-add. Assume source
> is qcow2 image. On blockdev-add we should specify aio and cache options
> for file child of qcow2 node. What happens next:
> 
> drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
> But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is
> places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
> as file-posix parse options and simply set s->use_linux_aio.
> 

No complaints from me, especially if Virtuozzo is on board. I would like 
to see some documentation changes alongside this deprecation, though.

> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> 
> Hi all! I remember, I suggested to deprecate drive-backup some time ago,
> and nobody complain.. But that old patch was inside the series with
> other more questionable deprecations and it did not landed.
> 
> Let's finally deprecate what should be deprecated long ago.
> 
> We now faced a problem in our downstream, described in commit message.
> In downstream I've fixed it by simply enabling O_DIRECT and linux_aio
> unconditionally for drive_backup target. But actually this just shows
> that using drive-backup in blockdev era is a bad idea. So let's motivate
> everyone (including Virtuozzo of course) to move to new interfaces and
> avoid problems with all that outdated option inheritance.
> 
>   docs/system/deprecated.rst | 5 +++++
>   qapi/block-core.json       | 5 ++++-
>   2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
> index 80cae86252..b6f5766e17 100644
> --- a/docs/system/deprecated.rst
> +++ b/docs/system/deprecated.rst
> @@ -186,6 +186,11 @@ Use the more generic commands ``block-export-add`` and ``block-export-del``
>   instead.  As part of this deprecation, where ``nbd-server-add`` used a
>   single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
>   
> +``drive-backup`` (since 6.0)
> +''''''''''''''''''''''''''''
> +
> +Use ``blockdev-backup`` in pair with ``blockdev-add`` instead.
> +

1) Let's add a sphinx reference to 
https://qemu-project.gitlab.io/qemu/interop/live-block-operations.html#live-disk-backup-drive-backup-and-blockdev-backup


2) Just a thought, not a request: We also may wish to update 
https://qemu-project.gitlab.io/qemu/interop/bitmaps.html to use the new, 
preferred method. However, this doc is a bit old and is in need of an 
overhaul anyway (Especially to add the NBD pull workflow.) Since the doc 
is in need of an overhaul anyway, can we ask Kashyap to help us here, if 
he has time?


3) Let's add a small explanation here that outlines the differences in 
using these two commands. Here's a suggestion:

This change primarily separates the creation/opening process of the 
backup target with explicit, separate steps. BlockdevBackup uses mostly 
the same arguments as DriveBackup, except the "format" and "mode" 
options are removed in favor of using explicit "blockdev-create" and 
"blockdev-add" calls.

The "target" argument changes semantics. It no longer accepts filenames, 
and will now additionally accept arbitrary node names in addition to 
device names.


4) Also not a request: If we want to go above and beyond, it might be 
nice to spell out the exact steps required to transition from the old 
interface to the new one. Here's a (hasty) suggestion for how that might 
look:

- The MODE argument is deprecated.
   - "existing" is replaced by using "blockdev-add" commands.
   - "absolute-paths" is replaced by using "blockdev-add" and
     "blockdev-create" commands.

- The FORMAT argument is deprecated.
   - Format information is given to "blockdev-add"/"blockdev-create".

- The TARGET argument has new semantics:
   - Filenames are no longer supported, use blockdev-add/blockdev-create
     as necessary instead.
   - Device targets remain supported.


Example:

drive-backup $ARGS format=$FORMAT mode=$MODE target=$FILENAME becomes:

(taking some liberties with syntax to just illustrate the idea ...)

blockdev-create options={
     "driver": "file",
     "filename": $FILENAME,
     "size": 0,
}

blockdev-add arguments={
     "driver": "file",
     "filename": $FILENAME,
     "node-name": "Example_Filenode0"
}

blockdev-create options={
     "driver": $FORMAT,
     "file": "Example_Filenode0",
     "size": $SIZE,
}

blockdev-add arguments={
     "driver": $FORMAT,
     "file": "Example_Filenode0",
     "node-name": "Example_Formatnode0",
}

blockdev-backup arguments={
     $ARGS ...,
     "target": "Example_Formatnode0",
}


>   System accelerators
>   -------------------
>   
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 6d227924d0..8e2c6e1622 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -1642,6 +1642,9 @@
>   # The operation can be stopped before it has completed using the
>   # block-job-cancel command.
>   #
> +# Features:
> +# @deprecated: This command is deprecated. Use @blockdev-backup instead.
> +#
>   # Returns: - nothing on success
>   #          - If @device is not a valid block device, GenericError
>   #
> @@ -1657,7 +1660,7 @@
>   #
>   ##
>   { 'command': 'drive-backup', 'boxed': true,
> -  'data': 'DriveBackup' }
> +  'data': 'DriveBackup', 'features': ['deprecated'] }
>   
>   ##
>   # @blockdev-backup:
> 

thanks,
--js

Re: [PATCH] qapi: deprecate drive-backup

Posted by Kashyap Chamarthy 1 week, 4 days ago
On Mon, Apr 26, 2021 at 01:34:17PM -0400, John Snow wrote:
> On 4/23/21 8:59 AM, Vladimir Sementsov-Ogievskiy wrote:
> > Modern way is using blockdev-add + blockdev-backup, which provides a
> > lot more control on how target is opened.

[...]

> 1) Let's add a sphinx reference to
> https://qemu-project.gitlab.io/qemu/interop/live-block-operations.html#live-disk-backup-drive-backup-and-blockdev-backup
> 
> 
> 2) Just a thought, not a request: We also may wish to update
> https://qemu-project.gitlab.io/qemu/interop/bitmaps.html to use the
> new, preferred method. However, this doc is a bit old and is in need
> of an overhaul anyway (Especially to add the NBD pull workflow.) Since
> the doc is in need of an overhaul anyway, can we ask Kashyap to help
> us here, if he has time?

Yes, I should be able to make time and help here; been putting it off on
the back burner.  Thanks for the reminder.  :) I'd like to update both
these:

    https://qemu-project.gitlab.io/qemu/interop/bitmaps.html
    https://qemu-project.gitlab.io/qemu/interop/live-block-operations.html

Both of them, as you know, refer to 'drive-backup'.  They also need
other adjustments / additions.  Also perhaps break the larger doc into a
couple of smaller ones.

I'll start working on it the end of this week.  First I need to tinker
with some of the recent improvements to refresh my memory and get a
sense of the modifications involved.  So please bear with me.

> 3) Let's add a small explanation here that outlines the differences in
> using these two commands. Here's a suggestion:
> 
> This change primarily separates the creation/opening process of the
> backup target with explicit, separate steps. BlockdevBackup uses
> mostly the same arguments as DriveBackup, except the "format" and
> "mode" options are removed in favor of using explicit
> "blockdev-create" and "blockdev-add" calls.
> 
> The "target" argument changes semantics. It no longer accepts
> filenames, and will now additionally accept arbitrary node names in
> addition to device names.

Yeah; this is something I had figure out by some trial-and-error when I
was playing with it in the past.

> 4) Also not a request: If we want to go above and beyond, it might be nice
> to spell out the exact steps required to transition from the old interface
> to the new one. Here's a (hasty) suggestion for how that might look:
> 
> - The MODE argument is deprecated.
>   - "existing" is replaced by using "blockdev-add" commands.
>   - "absolute-paths" is replaced by using "blockdev-add" and
>     "blockdev-create" commands.
> 
> - The FORMAT argument is deprecated.
>   - Format information is given to "blockdev-add"/"blockdev-create".
> 
> - The TARGET argument has new semantics:
>   - Filenames are no longer supported, use blockdev-add/blockdev-create
>     as necessary instead.
>   - Device targets remain supported.

Agreed; docs like these can be useful for management tools that rely on
the old behaviour and are not as up-to-date as libvirt in keeping track
of QEMU developments.

[...]

-- 
/kashyap

Re: [PATCH] qapi: deprecate drive-backup

Posted by Vladimir Sementsov-Ogievskiy 1 week, 5 days ago
26.04.2021 20:34, John Snow wrote:
> On 4/23/21 8:59 AM, Vladimir Sementsov-Ogievskiy wrote:
>> Modern way is using blockdev-add + blockdev-backup, which provides a
>> lot more control on how target is opened.
>>
>> As example of drive-backup problems consider the following:
>>
>> User of drive-backup expects that target will be opened in the same
>> cache and aio mode as source. Corresponding logic is in
>> drive_backup_prepare(), where we take bs->open_flags of source.
>>
>> It works rather bad if source was added by blockdev-add. Assume source
>> is qcow2 image. On blockdev-add we should specify aio and cache options
>> for file child of qcow2 node. What happens next:
>>
>> drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
>> But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is
>> places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
>> as file-posix parse options and simply set s->use_linux_aio.
>>
> 
> No complaints from me, especially if Virtuozzo is on board. I would like to see some documentation changes alongside this deprecation, though.
> 
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> ---
>>
>> Hi all! I remember, I suggested to deprecate drive-backup some time ago,
>> and nobody complain.. But that old patch was inside the series with
>> other more questionable deprecations and it did not landed.
>>
>> Let's finally deprecate what should be deprecated long ago.
>>
>> We now faced a problem in our downstream, described in commit message.
>> In downstream I've fixed it by simply enabling O_DIRECT and linux_aio
>> unconditionally for drive_backup target. But actually this just shows
>> that using drive-backup in blockdev era is a bad idea. So let's motivate
>> everyone (including Virtuozzo of course) to move to new interfaces and
>> avoid problems with all that outdated option inheritance.
>>
>>   docs/system/deprecated.rst | 5 +++++
>>   qapi/block-core.json       | 5 ++++-
>>   2 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
>> index 80cae86252..b6f5766e17 100644
>> --- a/docs/system/deprecated.rst
>> +++ b/docs/system/deprecated.rst
>> @@ -186,6 +186,11 @@ Use the more generic commands ``block-export-add`` and ``block-export-del``
>>   instead.  As part of this deprecation, where ``nbd-server-add`` used a
>>   single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
>> +``drive-backup`` (since 6.0)
>> +''''''''''''''''''''''''''''
>> +
>> +Use ``blockdev-backup`` in pair with ``blockdev-add`` instead.
>> +
> 
> 1) Let's add a sphinx reference to https://qemu-project.gitlab.io/qemu/interop/live-block-operations.html#live-disk-backup-drive-backup-and-blockdev-backup
> 
> 
> 2) Just a thought, not a request: We also may wish to update https://qemu-project.gitlab.io/qemu/interop/bitmaps.html to use the new, preferred method. However, this doc is a bit old and is in need of an overhaul anyway (Especially to add the NBD pull workflow.) Since the doc is in need of an overhaul anyway, can we ask Kashyap to help us here, if he has time?
> 
> 
> 3) Let's add a small explanation here that outlines the differences in using these two commands. Here's a suggestion:
> 
> This change primarily separates the creation/opening process of the backup target with explicit, separate steps. BlockdevBackup uses mostly the same arguments as DriveBackup, except the "format" and "mode" options are removed in favor of using explicit "blockdev-create" and "blockdev-add" calls.
> 
> The "target" argument changes semantics. It no longer accepts filenames, and will now additionally accept arbitrary node names in addition to device names.
> 
> 
> 4) Also not a request: If we want to go above and beyond, it might be nice to spell out the exact steps required to transition from the old interface to the new one. Here's a (hasty) suggestion for how that might look:
> 
> - The MODE argument is deprecated.
>   - "existing" is replaced by using "blockdev-add" commands.
>   - "absolute-paths" is replaced by using "blockdev-add" and
>     "blockdev-create" commands.
> 
> - The FORMAT argument is deprecated.
>   - Format information is given to "blockdev-add"/"blockdev-create".
> 
> - The TARGET argument has new semantics:
>   - Filenames are no longer supported, use blockdev-add/blockdev-create
>     as necessary instead.
>   - Device targets remain supported.
> 
> 
> Example:
> 
> drive-backup $ARGS format=$FORMAT mode=$MODE target=$FILENAME becomes:
> 
> (taking some liberties with syntax to just illustrate the idea ...)
> 
> blockdev-create options={
>     "driver": "file",
>     "filename": $FILENAME,
>     "size": 0,
> }
> 
> blockdev-add arguments={
>     "driver": "file",
>     "filename": $FILENAME,
>     "node-name": "Example_Filenode0"
> }
> 
> blockdev-create options={
>     "driver": $FORMAT,
>     "file": "Example_Filenode0",
>     "size": $SIZE,
> }
> 
> blockdev-add arguments={
>     "driver": $FORMAT,
>     "file": "Example_Filenode0",
>     "node-name": "Example_Formatnode0",
> }
> 
> blockdev-backup arguments={
>     $ARGS ...,
>     "target": "Example_Formatnode0",
> }
> 

Good ideas. Hmm. Do you think that the whole explanation with examples should be here, in docs/system/deprecated.rst ? Seems too big in comparison with other deprecations


-- 
Best regards,
Vladimir


Re: [PATCH] qapi: deprecate drive-backup

Posted by Daniel P. Berrangé 1 week, 5 days ago
On Mon, Apr 26, 2021 at 09:00:36PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> 26.04.2021 20:34, John Snow wrote:
> > On 4/23/21 8:59 AM, Vladimir Sementsov-Ogievskiy wrote:
> > > Modern way is using blockdev-add + blockdev-backup, which provides a
> > > lot more control on how target is opened.
> > > 
> > > As example of drive-backup problems consider the following:
> > > 
> > > User of drive-backup expects that target will be opened in the same
> > > cache and aio mode as source. Corresponding logic is in
> > > drive_backup_prepare(), where we take bs->open_flags of source.
> > > 
> > > It works rather bad if source was added by blockdev-add. Assume source
> > > is qcow2 image. On blockdev-add we should specify aio and cache options
> > > for file child of qcow2 node. What happens next:
> > > 
> > > drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
> > > But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is
> > > places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
> > > as file-posix parse options and simply set s->use_linux_aio.
> > > 
> > 
> > No complaints from me, especially if Virtuozzo is on board. I would like to see some documentation changes alongside this deprecation, though.
> > 
> > > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> > > ---
> > > 
> > > Hi all! I remember, I suggested to deprecate drive-backup some time ago,
> > > and nobody complain.. But that old patch was inside the series with
> > > other more questionable deprecations and it did not landed.
> > > 
> > > Let's finally deprecate what should be deprecated long ago.
> > > 
> > > We now faced a problem in our downstream, described in commit message.
> > > In downstream I've fixed it by simply enabling O_DIRECT and linux_aio
> > > unconditionally for drive_backup target. But actually this just shows
> > > that using drive-backup in blockdev era is a bad idea. So let's motivate
> > > everyone (including Virtuozzo of course) to move to new interfaces and
> > > avoid problems with all that outdated option inheritance.
> > > 
> > >   docs/system/deprecated.rst | 5 +++++
> > >   qapi/block-core.json       | 5 ++++-
> > >   2 files changed, 9 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
> > > index 80cae86252..b6f5766e17 100644
> > > --- a/docs/system/deprecated.rst
> > > +++ b/docs/system/deprecated.rst
> > > @@ -186,6 +186,11 @@ Use the more generic commands ``block-export-add`` and ``block-export-del``
> > >   instead.  As part of this deprecation, where ``nbd-server-add`` used a
> > >   single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
> > > +``drive-backup`` (since 6.0)
> > > +''''''''''''''''''''''''''''
> > > +
> > > +Use ``blockdev-backup`` in pair with ``blockdev-add`` instead.
> > > +
> > 
> > 1) Let's add a sphinx reference to https://qemu-project.gitlab.io/qemu/interop/live-block-operations.html#live-disk-backup-drive-backup-and-blockdev-backup
> > 
> > 
> > 2) Just a thought, not a request: We also may wish to update https://qemu-project.gitlab.io/qemu/interop/bitmaps.html to use the new, preferred method. However, this doc is a bit old and is in need of an overhaul anyway (Especially to add the NBD pull workflow.) Since the doc is in need of an overhaul anyway, can we ask Kashyap to help us here, if he has time?
> > 
> > 
> > 3) Let's add a small explanation here that outlines the differences in using these two commands. Here's a suggestion:
> > 
> > This change primarily separates the creation/opening process of the backup target with explicit, separate steps. BlockdevBackup uses mostly the same arguments as DriveBackup, except the "format" and "mode" options are removed in favor of using explicit "blockdev-create" and "blockdev-add" calls.
> > 
> > The "target" argument changes semantics. It no longer accepts filenames, and will now additionally accept arbitrary node names in addition to device names.
> > 
> > 
> > 4) Also not a request: If we want to go above and beyond, it might be nice to spell out the exact steps required to transition from the old interface to the new one. Here's a (hasty) suggestion for how that might look:
> > 
> > - The MODE argument is deprecated.
> >   - "existing" is replaced by using "blockdev-add" commands.
> >   - "absolute-paths" is replaced by using "blockdev-add" and
> >     "blockdev-create" commands.
> > 
> > - The FORMAT argument is deprecated.
> >   - Format information is given to "blockdev-add"/"blockdev-create".
> > 
> > - The TARGET argument has new semantics:
> >   - Filenames are no longer supported, use blockdev-add/blockdev-create
> >     as necessary instead.
> >   - Device targets remain supported.
> > 
> > 
> > Example:
> > 
> > drive-backup $ARGS format=$FORMAT mode=$MODE target=$FILENAME becomes:
> > 
> > (taking some liberties with syntax to just illustrate the idea ...)
> > 
> > blockdev-create options={
> >     "driver": "file",
> >     "filename": $FILENAME,
> >     "size": 0,
> > }
> > 
> > blockdev-add arguments={
> >     "driver": "file",
> >     "filename": $FILENAME,
> >     "node-name": "Example_Filenode0"
> > }
> > 
> > blockdev-create options={
> >     "driver": $FORMAT,
> >     "file": "Example_Filenode0",
> >     "size": $SIZE,
> > }
> > 
> > blockdev-add arguments={
> >     "driver": $FORMAT,
> >     "file": "Example_Filenode0",
> >     "node-name": "Example_Formatnode0",
> > }
> > 
> > blockdev-backup arguments={
> >     $ARGS ...,
> >     "target": "Example_Formatnode0",
> > }
> > 
> 
> Good ideas. Hmm. Do you think that the whole explanation with examples should be here, in docs/system/deprecated.rst ? Seems too big in comparison with other deprecations

No, the deprecations entry should be short.

If the replacement is so complex that it requires us to provide examples,
that's a sign that the replacement is insufficiently documented in its
own right. IOW, add all this docs info to a suitable place in the main
QEMU documentation, and just link to that from the deprecations page.


Regards,
Daniel
-- 
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|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
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Re: [PATCH] qapi: deprecate drive-backup

Posted by John Snow 1 week, 5 days ago
On 4/26/21 2:05 PM, Daniel P. Berrangé wrote:
> On Mon, Apr 26, 2021 at 09:00:36PM +0300, Vladimir Sementsov-Ogievskiy wrote:
>> 26.04.2021 20:34, John Snow wrote:
>>> On 4/23/21 8:59 AM, Vladimir Sementsov-Ogievskiy wrote:
>>>> Modern way is using blockdev-add + blockdev-backup, which provides a
>>>> lot more control on how target is opened.
>>>>
>>>> As example of drive-backup problems consider the following:
>>>>
>>>> User of drive-backup expects that target will be opened in the same
>>>> cache and aio mode as source. Corresponding logic is in
>>>> drive_backup_prepare(), where we take bs->open_flags of source.
>>>>
>>>> It works rather bad if source was added by blockdev-add. Assume source
>>>> is qcow2 image. On blockdev-add we should specify aio and cache options
>>>> for file child of qcow2 node. What happens next:
>>>>
>>>> drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
>>>> But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is
>>>> places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
>>>> as file-posix parse options and simply set s->use_linux_aio.
>>>>
>>>
>>> No complaints from me, especially if Virtuozzo is on board. I would like to see some documentation changes alongside this deprecation, though.
>>>
>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>>> ---
>>>>
>>>> Hi all! I remember, I suggested to deprecate drive-backup some time ago,
>>>> and nobody complain.. But that old patch was inside the series with
>>>> other more questionable deprecations and it did not landed.
>>>>
>>>> Let's finally deprecate what should be deprecated long ago.
>>>>
>>>> We now faced a problem in our downstream, described in commit message.
>>>> In downstream I've fixed it by simply enabling O_DIRECT and linux_aio
>>>> unconditionally for drive_backup target. But actually this just shows
>>>> that using drive-backup in blockdev era is a bad idea. So let's motivate
>>>> everyone (including Virtuozzo of course) to move to new interfaces and
>>>> avoid problems with all that outdated option inheritance.
>>>>
>>>>    docs/system/deprecated.rst | 5 +++++
>>>>    qapi/block-core.json       | 5 ++++-
>>>>    2 files changed, 9 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
>>>> index 80cae86252..b6f5766e17 100644
>>>> --- a/docs/system/deprecated.rst
>>>> +++ b/docs/system/deprecated.rst
>>>> @@ -186,6 +186,11 @@ Use the more generic commands ``block-export-add`` and ``block-export-del``
>>>>    instead.  As part of this deprecation, where ``nbd-server-add`` used a
>>>>    single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
>>>> +``drive-backup`` (since 6.0)
>>>> +''''''''''''''''''''''''''''
>>>> +
>>>> +Use ``blockdev-backup`` in pair with ``blockdev-add`` instead.
>>>> +
>>>
>>> 1) Let's add a sphinx reference to https://qemu-project.gitlab.io/qemu/interop/live-block-operations.html#live-disk-backup-drive-backup-and-blockdev-backup
>>>
>>>
>>> 2) Just a thought, not a request: We also may wish to update https://qemu-project.gitlab.io/qemu/interop/bitmaps.html to use the new, preferred method. However, this doc is a bit old and is in need of an overhaul anyway (Especially to add the NBD pull workflow.) Since the doc is in need of an overhaul anyway, can we ask Kashyap to help us here, if he has time?
>>>
>>>
>>> 3) Let's add a small explanation here that outlines the differences in using these two commands. Here's a suggestion:
>>>
>>> This change primarily separates the creation/opening process of the backup target with explicit, separate steps. BlockdevBackup uses mostly the same arguments as DriveBackup, except the "format" and "mode" options are removed in favor of using explicit "blockdev-create" and "blockdev-add" calls.
>>>
>>> The "target" argument changes semantics. It no longer accepts filenames, and will now additionally accept arbitrary node names in addition to device names.
>>>
>>>
>>> 4) Also not a request: If we want to go above and beyond, it might be nice to spell out the exact steps required to transition from the old interface to the new one. Here's a (hasty) suggestion for how that might look:
>>>
>>> - The MODE argument is deprecated.
>>>    - "existing" is replaced by using "blockdev-add" commands.
>>>    - "absolute-paths" is replaced by using "blockdev-add" and
>>>      "blockdev-create" commands.
>>>
>>> - The FORMAT argument is deprecated.
>>>    - Format information is given to "blockdev-add"/"blockdev-create".
>>>
>>> - The TARGET argument has new semantics:
>>>    - Filenames are no longer supported, use blockdev-add/blockdev-create
>>>      as necessary instead.
>>>    - Device targets remain supported.
>>>
>>>
>>> Example:
>>>
>>> drive-backup $ARGS format=$FORMAT mode=$MODE target=$FILENAME becomes:
>>>
>>> (taking some liberties with syntax to just illustrate the idea ...)
>>>
>>> blockdev-create options={
>>>      "driver": "file",
>>>      "filename": $FILENAME,
>>>      "size": 0,
>>> }
>>>
>>> blockdev-add arguments={
>>>      "driver": "file",
>>>      "filename": $FILENAME,
>>>      "node-name": "Example_Filenode0"
>>> }
>>>
>>> blockdev-create options={
>>>      "driver": $FORMAT,
>>>      "file": "Example_Filenode0",
>>>      "size": $SIZE,
>>> }
>>>
>>> blockdev-add arguments={
>>>      "driver": $FORMAT,
>>>      "file": "Example_Filenode0",
>>>      "node-name": "Example_Formatnode0",
>>> }
>>>
>>> blockdev-backup arguments={
>>>      $ARGS ...,
>>>      "target": "Example_Formatnode0",
>>> }
>>>
>>
>> Good ideas. Hmm. Do you think that the whole explanation with examples should be here, in docs/system/deprecated.rst ? Seems too big in comparison with other deprecations
> 
> No, the deprecations entry should be short.
> 
> If the replacement is so complex that it requires us to provide examples,
> that's a sign that the replacement is insufficiently documented in its
> own right. IOW, add all this docs info to a suitable place in the main
> QEMU documentation, and just link to that from the deprecations page.
> 

Agree with Dan, keep the deprec section short.

Perhaps we can add an example to the live block ops doc that shows an 
example of how to transition and link to that example from here.

--js

> 
> Regards,
> Daniel
> 

Re: [PATCH] qapi: deprecate drive-backup

Posted by Vladimir Sementsov-Ogievskiy 1 week, 5 days ago
26.04.2021 21:30, John Snow wrote:
> On 4/26/21 2:05 PM, Daniel P. Berrangé wrote:
>> On Mon, Apr 26, 2021 at 09:00:36PM +0300, Vladimir Sementsov-Ogievskiy wrote:
>>> 26.04.2021 20:34, John Snow wrote:
>>>> On 4/23/21 8:59 AM, Vladimir Sementsov-Ogievskiy wrote:
>>>>> Modern way is using blockdev-add + blockdev-backup, which provides a
>>>>> lot more control on how target is opened.
>>>>>
>>>>> As example of drive-backup problems consider the following:
>>>>>
>>>>> User of drive-backup expects that target will be opened in the same
>>>>> cache and aio mode as source. Corresponding logic is in
>>>>> drive_backup_prepare(), where we take bs->open_flags of source.
>>>>>
>>>>> It works rather bad if source was added by blockdev-add. Assume source
>>>>> is qcow2 image. On blockdev-add we should specify aio and cache options
>>>>> for file child of qcow2 node. What happens next:
>>>>>
>>>>> drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
>>>>> But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is
>>>>> places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
>>>>> as file-posix parse options and simply set s->use_linux_aio.
>>>>>
>>>>
>>>> No complaints from me, especially if Virtuozzo is on board. I would like to see some documentation changes alongside this deprecation, though.
>>>>
>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>>>> ---
>>>>>
>>>>> Hi all! I remember, I suggested to deprecate drive-backup some time ago,
>>>>> and nobody complain.. But that old patch was inside the series with
>>>>> other more questionable deprecations and it did not landed.
>>>>>
>>>>> Let's finally deprecate what should be deprecated long ago.
>>>>>
>>>>> We now faced a problem in our downstream, described in commit message.
>>>>> In downstream I've fixed it by simply enabling O_DIRECT and linux_aio
>>>>> unconditionally for drive_backup target. But actually this just shows
>>>>> that using drive-backup in blockdev era is a bad idea. So let's motivate
>>>>> everyone (including Virtuozzo of course) to move to new interfaces and
>>>>> avoid problems with all that outdated option inheritance.
>>>>>
>>>>>    docs/system/deprecated.rst | 5 +++++
>>>>>    qapi/block-core.json       | 5 ++++-
>>>>>    2 files changed, 9 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
>>>>> index 80cae86252..b6f5766e17 100644
>>>>> --- a/docs/system/deprecated.rst
>>>>> +++ b/docs/system/deprecated.rst
>>>>> @@ -186,6 +186,11 @@ Use the more generic commands ``block-export-add`` and ``block-export-del``
>>>>>    instead.  As part of this deprecation, where ``nbd-server-add`` used a
>>>>>    single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
>>>>> +``drive-backup`` (since 6.0)
>>>>> +''''''''''''''''''''''''''''
>>>>> +
>>>>> +Use ``blockdev-backup`` in pair with ``blockdev-add`` instead.
>>>>> +
>>>>
>>>> 1) Let's add a sphinx reference to https://qemu-project.gitlab.io/qemu/interop/live-block-operations.html#live-disk-backup-drive-backup-and-blockdev-backup
>>>>
>>>>
>>>> 2) Just a thought, not a request: We also may wish to update https://qemu-project.gitlab.io/qemu/interop/bitmaps.html to use the new, preferred method. However, this doc is a bit old and is in need of an overhaul anyway (Especially to add the NBD pull workflow.) Since the doc is in need of an overhaul anyway, can we ask Kashyap to help us here, if he has time?
>>>>
>>>>
>>>> 3) Let's add a small explanation here that outlines the differences in using these two commands. Here's a suggestion:
>>>>
>>>> This change primarily separates the creation/opening process of the backup target with explicit, separate steps. BlockdevBackup uses mostly the same arguments as DriveBackup, except the "format" and "mode" options are removed in favor of using explicit "blockdev-create" and "blockdev-add" calls.
>>>>
>>>> The "target" argument changes semantics. It no longer accepts filenames, and will now additionally accept arbitrary node names in addition to device names.
>>>>
>>>>
>>>> 4) Also not a request: If we want to go above and beyond, it might be nice to spell out the exact steps required to transition from the old interface to the new one. Here's a (hasty) suggestion for how that might look:
>>>>
>>>> - The MODE argument is deprecated.
>>>>    - "existing" is replaced by using "blockdev-add" commands.
>>>>    - "absolute-paths" is replaced by using "blockdev-add" and
>>>>      "blockdev-create" commands.
>>>>
>>>> - The FORMAT argument is deprecated.
>>>>    - Format information is given to "blockdev-add"/"blockdev-create".
>>>>
>>>> - The TARGET argument has new semantics:
>>>>    - Filenames are no longer supported, use blockdev-add/blockdev-create
>>>>      as necessary instead.
>>>>    - Device targets remain supported.
>>>>
>>>>
>>>> Example:
>>>>
>>>> drive-backup $ARGS format=$FORMAT mode=$MODE target=$FILENAME becomes:
>>>>
>>>> (taking some liberties with syntax to just illustrate the idea ...)
>>>>
>>>> blockdev-create options={
>>>>      "driver": "file",
>>>>      "filename": $FILENAME,
>>>>      "size": 0,
>>>> }
>>>>
>>>> blockdev-add arguments={
>>>>      "driver": "file",
>>>>      "filename": $FILENAME,
>>>>      "node-name": "Example_Filenode0"
>>>> }
>>>>
>>>> blockdev-create options={
>>>>      "driver": $FORMAT,
>>>>      "file": "Example_Filenode0",
>>>>      "size": $SIZE,
>>>> }
>>>>
>>>> blockdev-add arguments={
>>>>      "driver": $FORMAT,
>>>>      "file": "Example_Filenode0",
>>>>      "node-name": "Example_Formatnode0",
>>>> }
>>>>
>>>> blockdev-backup arguments={
>>>>      $ARGS ...,
>>>>      "target": "Example_Formatnode0",
>>>> }
>>>>
>>>
>>> Good ideas. Hmm. Do you think that the whole explanation with examples should be here, in docs/system/deprecated.rst ? Seems too big in comparison with other deprecations
>>
>> No, the deprecations entry should be short.
>>
>> If the replacement is so complex that it requires us to provide examples,
>> that's a sign that the replacement is insufficiently documented in its
>> own right. IOW, add all this docs info to a suitable place in the main
>> QEMU documentation, and just link to that from the deprecations page.
>>
> 
> Agree with Dan, keep the deprec section short.
> 
> Perhaps we can add an example to the live block ops doc that shows an example of how to transition and link to that example from here.
> 

OK, will do


-- 
Best regards,
Vladimir


Re: [PATCH] qapi: deprecate drive-backup

Posted by John Snow 1 week, 5 days ago
On 4/26/21 2:41 PM, Vladimir Sementsov-Ogievskiy wrote:
> 26.04.2021 21:30, John Snow wrote:
>> On 4/26/21 2:05 PM, Daniel P. Berrangé wrote:
>>> On Mon, Apr 26, 2021 at 09:00:36PM +0300, Vladimir 
>>> Sementsov-Ogievskiy wrote:
>>>> 26.04.2021 20:34, John Snow wrote:
>>>>> On 4/23/21 8:59 AM, Vladimir Sementsov-Ogievskiy wrote:
>>>>>> Modern way is using blockdev-add + blockdev-backup, which provides a
>>>>>> lot more control on how target is opened.
>>>>>>
>>>>>> As example of drive-backup problems consider the following:
>>>>>>
>>>>>> User of drive-backup expects that target will be opened in the same
>>>>>> cache and aio mode as source. Corresponding logic is in
>>>>>> drive_backup_prepare(), where we take bs->open_flags of source.
>>>>>>
>>>>>> It works rather bad if source was added by blockdev-add. Assume 
>>>>>> source
>>>>>> is qcow2 image. On blockdev-add we should specify aio and cache 
>>>>>> options
>>>>>> for file child of qcow2 node. What happens next:
>>>>>>
>>>>>> drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
>>>>>> But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: 
>>>>>> BDRV_O_NOCAHE is
>>>>>> places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
>>>>>> as file-posix parse options and simply set s->use_linux_aio.
>>>>>>
>>>>>
>>>>> No complaints from me, especially if Virtuozzo is on board. I would 
>>>>> like to see some documentation changes alongside this deprecation, 
>>>>> though.
>>>>>
>>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy 
>>>>>> <vsementsov@virtuozzo.com>
>>>>>> ---
>>>>>>
>>>>>> Hi all! I remember, I suggested to deprecate drive-backup some 
>>>>>> time ago,
>>>>>> and nobody complain.. But that old patch was inside the series with
>>>>>> other more questionable deprecations and it did not landed.
>>>>>>
>>>>>> Let's finally deprecate what should be deprecated long ago.
>>>>>>
>>>>>> We now faced a problem in our downstream, described in commit 
>>>>>> message.
>>>>>> In downstream I've fixed it by simply enabling O_DIRECT and linux_aio
>>>>>> unconditionally for drive_backup target. But actually this just shows
>>>>>> that using drive-backup in blockdev era is a bad idea. So let's 
>>>>>> motivate
>>>>>> everyone (including Virtuozzo of course) to move to new interfaces 
>>>>>> and
>>>>>> avoid problems with all that outdated option inheritance.
>>>>>>
>>>>>>    docs/system/deprecated.rst | 5 +++++
>>>>>>    qapi/block-core.json       | 5 ++++-
>>>>>>    2 files changed, 9 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
>>>>>> index 80cae86252..b6f5766e17 100644
>>>>>> --- a/docs/system/deprecated.rst
>>>>>> +++ b/docs/system/deprecated.rst
>>>>>> @@ -186,6 +186,11 @@ Use the more generic commands 
>>>>>> ``block-export-add`` and ``block-export-del``
>>>>>>    instead.  As part of this deprecation, where ``nbd-server-add`` 
>>>>>> used a
>>>>>>    single ``bitmap``, the new ``block-export-add`` uses a list of 
>>>>>> ``bitmaps``.
>>>>>> +``drive-backup`` (since 6.0)
>>>>>> +''''''''''''''''''''''''''''
>>>>>> +
>>>>>> +Use ``blockdev-backup`` in pair with ``blockdev-add`` instead.
>>>>>> +
>>>>>
>>>>> 1) Let's add a sphinx reference to 
>>>>> https://qemu-project.gitlab.io/qemu/interop/live-block-operations.html#live-disk-backup-drive-backup-and-blockdev-backup 
>>>>>
>>>>>
>>>>>
>>>>> 2) Just a thought, not a request: We also may wish to update 
>>>>> https://qemu-project.gitlab.io/qemu/interop/bitmaps.html to use the 
>>>>> new, preferred method. However, this doc is a bit old and is in 
>>>>> need of an overhaul anyway (Especially to add the NBD pull 
>>>>> workflow.) Since the doc is in need of an overhaul anyway, can we 
>>>>> ask Kashyap to help us here, if he has time?
>>>>>
>>>>>
>>>>> 3) Let's add a small explanation here that outlines the differences 
>>>>> in using these two commands. Here's a suggestion:
>>>>>
>>>>> This change primarily separates the creation/opening process of the 
>>>>> backup target with explicit, separate steps. BlockdevBackup uses 
>>>>> mostly the same arguments as DriveBackup, except the "format" and 
>>>>> "mode" options are removed in favor of using explicit 
>>>>> "blockdev-create" and "blockdev-add" calls.
>>>>>

(Here, I accidentally used the names of the argument objects instead of 
the names of the commands. It's likely better to spell out the names of 
the commands instead.)

>>>>> The "target" argument changes semantics. It no longer accepts 
>>>>> filenames, and will now additionally accept arbitrary node names in 
>>>>> addition to device names.
>>>>>
>>>>>
>>>>> 4) Also not a request: If we want to go above and beyond, it might 
>>>>> be nice to spell out the exact steps required to transition from 
>>>>> the old interface to the new one. Here's a (hasty) suggestion for 
>>>>> how that might look:
>>>>>
>>>>> - The MODE argument is deprecated.
>>>>>    - "existing" is replaced by using "blockdev-add" commands.
>>>>>    - "absolute-paths" is replaced by using "blockdev-add" and
>>>>>      "blockdev-create" commands.
>>>>>
>>>>> - The FORMAT argument is deprecated.
>>>>>    - Format information is given to "blockdev-add"/"blockdev-create".
>>>>>
>>>>> - The TARGET argument has new semantics:
>>>>>    - Filenames are no longer supported, use 
>>>>> blockdev-add/blockdev-create
>>>>>      as necessary instead.
>>>>>    - Device targets remain supported.
>>>>>
>>>>>
>>>>> Example:
>>>>>
>>>>> drive-backup $ARGS format=$FORMAT mode=$MODE target=$FILENAME becomes:
>>>>>
>>>>> (taking some liberties with syntax to just illustrate the idea ...)
>>>>>
>>>>> blockdev-create options={
>>>>>      "driver": "file",
>>>>>      "filename": $FILENAME,
>>>>>      "size": 0,
>>>>> }
>>>>>
>>>>> blockdev-add arguments={
>>>>>      "driver": "file",
>>>>>      "filename": $FILENAME,
>>>>>      "node-name": "Example_Filenode0"
>>>>> }
>>>>>
>>>>> blockdev-create options={
>>>>>      "driver": $FORMAT,
>>>>>      "file": "Example_Filenode0",
>>>>>      "size": $SIZE,
>>>>> }
>>>>>
>>>>> blockdev-add arguments={
>>>>>      "driver": $FORMAT,
>>>>>      "file": "Example_Filenode0",
>>>>>      "node-name": "Example_Formatnode0",
>>>>> }
>>>>>
>>>>> blockdev-backup arguments={
>>>>>      $ARGS ...,
>>>>>      "target": "Example_Formatnode0",
>>>>> }
>>>>>
>>>>
>>>> Good ideas. Hmm. Do you think that the whole explanation with 
>>>> examples should be here, in docs/system/deprecated.rst ? Seems too 
>>>> big in comparison with other deprecations
>>>
>>> No, the deprecations entry should be short.
>>>
>>> If the replacement is so complex that it requires us to provide 
>>> examples,
>>> that's a sign that the replacement is insufficiently documented in its
>>> own right. IOW, add all this docs info to a suitable place in the main
>>> QEMU documentation, and just link to that from the deprecations page.
>>>
>>
>> Agree with Dan, keep the deprec section short.
>>
>> Perhaps we can add an example to the live block ops doc that shows an 
>> example of how to transition and link to that example from here.
>>
> 
> OK, will do
> 
> 

Thanks! I'm sure Eric and I can help copy-edit. It will be nice to get 
rid of a confusing, mostly duplicated interface.

(Even if it is very convenient ...)

It's likely we'll want some iotests functions to help streamline the 
process. Important things for me to consider while working on an API 
helper library, too.

--js

Re: [PATCH] qapi: deprecate drive-backup

Posted by Peter Krempa 1 week, 5 days ago
On Fri, Apr 23, 2021 at 15:59:00 +0300, Vladimir Sementsov-Ogievskiy wrote:
> Modern way is using blockdev-add + blockdev-backup, which provides a
> lot more control on how target is opened.
> 
> As example of drive-backup problems consider the following:
> 
> User of drive-backup expects that target will be opened in the same
> cache and aio mode as source. Corresponding logic is in
> drive_backup_prepare(), where we take bs->open_flags of source.
> 
> It works rather bad if source was added by blockdev-add. Assume source
> is qcow2 image. On blockdev-add we should specify aio and cache options
> for file child of qcow2 node. What happens next:
> 
> drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
> But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is
> places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
> as file-posix parse options and simply set s->use_linux_aio.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> 
> Hi all! I remember, I suggested to deprecate drive-backup some time ago,
> and nobody complain.. But that old patch was inside the series with
> other more questionable deprecations and it did not landed.
> 
> Let's finally deprecate what should be deprecated long ago.
> 
> We now faced a problem in our downstream, described in commit message.
> In downstream I've fixed it by simply enabling O_DIRECT and linux_aio
> unconditionally for drive_backup target. But actually this just shows
> that using drive-backup in blockdev era is a bad idea. So let's motivate
> everyone (including Virtuozzo of course) to move to new interfaces and
> avoid problems with all that outdated option inheritance.

libvirt never used 'drive-backup' thus

Reviewed-by: Peter Krempa <pkrempa@redhat.com>