Re: [PATCH v4 4/4] Documentation: add debugfs description for hisi migration

[Alex Williamson]

On Tue, 2 Apr 2024 11:24:32 +0800
Longfang Liu <liulongfang@xxxxxxxxxx> wrote:

> Add a debugfs document description file to help users understand
> how to use the hisilicon accelerator live migration driver's
> debugfs.
> 
> Update the file paths that need to be maintained in MAINTAINERS
> 
> Signed-off-by: Longfang Liu <liulongfang@xxxxxxxxxx>
> ---
>  .../ABI/testing/debugfs-hisi-migration        | 34 +++++++++++++++++++
>  MAINTAINERS                                   |  1 +
>  2 files changed, 35 insertions(+)
>  create mode 100644 Documentation/ABI/testing/debugfs-hisi-migration
> 
> diff --git a/Documentation/ABI/testing/debugfs-hisi-migration b/Documentation/ABI/testing/debugfs-hisi-migration
> new file mode 100644
> index 000000000000..3d7339276e6f
> --- /dev/null
> +++ b/Documentation/ABI/testing/debugfs-hisi-migration
> @@ -0,0 +1,34 @@
> +What:		/sys/kernel/debug/vfio/<device>/migration/hisi_acc/data
> +Date:		Apr 2024
> +KernelVersion:  6.9

At best 6.10 with a merge window in May.

> +Contact:	Longfang Liu <liulongfang@xxxxxxxxxx>
> +Description:	Read the live migration data of the vfio device.
> +		These data include device status data, queue configuration
> +		data and some task configuration data.
> +		The output format of the data is defined by the live
> +		migration driver.

"Dumps the device debug migration buffer, state must first be saved
using the 'save' attribute."

> +
> +What:		/sys/kernel/debug/vfio/<device>/migration/hisi_acc/attr
> +Date:		Apr 2024
> +KernelVersion:  6.9
> +Contact:	Longfang Liu <liulongfang@xxxxxxxxxx>
> +Description:	Read the live migration attributes of the vfio device.
> +		it include device status attributes and data length attributes
> +		The output format of the attributes is defined by the live
> +		migration driver.

AFAICT from the previous patch, this attribute is useless.

> +
> +What:		/sys/kernel/debug/vfio/<device>/migration/hisi_acc/cmd_state
> +Date:		Apr 2024
> +KernelVersion:  6.9
> +Contact:	Longfang Liu <liulongfang@xxxxxxxxxx>
> +Description:	Used to obtain the device command sending and receiving
> +		channel status. If successful, returns the command value.
> +		If failed, return error log.
> +

Seems like it statically returns "OK" plus the actual value.


> +What:		/sys/kernel/debug/vfio/<device>/migration/hisi_acc/save
> +Date:		Apr 2024
> +KernelVersion:  6.9
> +Contact:	Longfang Liu <liulongfang@xxxxxxxxxx>
> +Description:	Trigger the Hisilicon accelerator device to perform
> +		the state saving operation of live migration through the read
> +		operation, and output the operation log results.

These interfaces are confusing, attr and data only work if there has
either been a previous save OR the user migration process closed saving
or resuming fds in the interim, and the user doesn't know which one
they get.  Note that debug_migf isn't even discarded between
open/close, only cmd and save require the device to be opened by a
user, data and attr might continue to return data from some previous
user save, resume, or debugfs save.



> diff --git a/MAINTAINERS b/MAINTAINERS
> index 7625911ec2f1..8c2d13b13273 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -23072,6 +23072,7 @@ M:	Longfang Liu <liulongfang@xxxxxxxxxx>
>  M:	Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>
>  L:	kvm@xxxxxxxxxxxxxxx
>  S:	Maintained
> +F:	Documentation/ABI/testing/debugfs-hisi-migration
>  F:	drivers/vfio/pci/hisilicon/
>  
>  VFIO MEDIATED DEVICE DRIVERS