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SubjectRe: [PATCH v9 13/22] s390: vfio-ap: sysfs interface to view matrix mdev matrix
On Mon, 13 Aug 2018 17:48:10 -0400
Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote:

> From: Tony Krowiak <akrowiak@linux.ibm.com>
>
> Provides a sysfs interface to view the AP matrix configured for the
> mediated matrix device.
>
> The relevant sysfs structures are:
>
> /sys/devices/vfio_ap/matrix/
> ...... [mdev_supported_types]
> ......... [vfio_ap-passthrough]
> ............ [devices]
> ...............[$uuid]
> .................. matrix
>
> To view the matrix configured for the mediated matrix device,
> print the matrix file:
>
> cat matrix
>
> Below are examples of the output from the above command:
>
> Example 1: Adapters and domains assigned
> Assignments:
> Adapters 5 and 6
> Domains 4 and 71 (0x47)
>
> Output
> 05.0004
> 05.0047
> 06.0004
> 06.0047
>
> Examples 2: Only adapters assigned
> Assignments:
> Adapters 5 and 6
>
> Output:
> 05.
> 06.
>
> Examples 3: Only domains assigned
> Assignments:
> Domains 4 and 71 (0x47)
>
> Output:
> .0004
> .0047

I find this output to be a bit confusing; but OTOH, I'm probably not
the person to parse it :) Still, some comments.

From previous discussions, ISTR that this is mainly supposed to be a
debugging/administration aid. Of course, this generates some questions:
- Should this be in sysfs (sysfs attributes are supposed to follow the
"one value per file" rule, at least for the most part), or would
debugfs be a better fit?
- Should userspace code be able to introspect the current
configuration? If yes, it might be better to have some
not-so-nice-but-easily-parsable output, possibly one attribute for
the assigned adapters and one for the assigned domains, and a tool
which distills that into a nice "matrix" with labeled rows and
columns for human consumption.

That said, I don't really have major objections to that interface.

>
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
> Tested-by: Michael Mueller <mimu@linux.ibm.com>
> Tested-by: Farhan Ali <alifm@linux.ibm.com>
> Tested-by: Pierre Morel <pmorel@linux.ibm.com>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
> drivers/s390/crypto/vfio_ap_ops.c | 52 +++++++++++++++++++++++++++++++++++++
> 1 files changed, 52 insertions(+), 0 deletions(-)

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