Subject: Re: [PATCH v3 0/5] Introduce variable length mdev alias

From: Cornelia Huck <[email-masked]>
Date: Tue, 17 Sep 2019 12:13:57 +0200

On Sun,  1 Sep 2019 23:24:31 -0500
Parav Pandit <[email-masked]> wrote:

> To have consistent naming for the netdevice of a mdev and to have
> consistent naming of the devlink port [1] of a mdev, which is formed using
> phys_port_name of the devlink port, current UUID is not usable because
> UUID is too long.
> 
> UUID in string format is 36-characters long and in binary 128-bit.
> Both formats are not able to fit within 15 characters limit of netdev
> name.
> 
> It is desired to have mdev device naming consistent using UUID.
> So that widely used user space framework such as ovs [2] can make use
> of mdev representor in similar way as PCIe SR-IOV VF and PF representors.
> 
> Hence,
> (a) mdev alias is created which is derived using sha1 from the mdev name.
> (b) Vendor driver describes how long an alias should be for the child mdev
> created for a given parent.
> (c) Mdev aliases are unique at system level.
> (d) alias is created optionally whenever parent requested.
> This ensures that non networking mdev parents can function without alias
> creation overhead.
> 
> This design is discussed at [3].
> 
> An example systemd/udev extension will have,
> 
> 1. netdev name created using mdev alias available in sysfs.
> 
> mdev UUID=83b8f4f2-509f-382f-3c1e-e6bfe0fa1001
> mdev 12 character alias=cd5b146a80a5
> 
> netdev name of this mdev = enmcd5b146a80a5
> Here en = Ethernet link
> m = mediated device
> 
> 2. devlink port phys_port_name created using mdev alias.
> devlink phys_port_name=pcd5b146a80a5
> 
> This patchset enables mdev core to maintain unique alias for a mdev.
> 
> Patch-1 Introduces mdev alias using sha1.
> Patch-2 Ensures that mdev alias is unique in a system.
> Patch-3 Exposes mdev alias in a sysfs hirerchy, update Documentation
> Patch-4 Introduces mdev_alias() API.
> Patch-5 Extends mtty driver to optionally provide alias generation.
> This also enables to test UUID based sha1 collision and trigger
> error handling for duplicate sha1 results.
> 
> [1] http://man7.org/linux/man-pages/man8/devlink-port.8.html
> [2] https://docs.openstack.org/os-vif/latest/user/plugins/ovs.html
> [3] https://patchwork.kernel.org/cover/11084231/
> 
> ---
> Changelog:
> v2->v3:
>  - Addressed comment from Yunsheng Lin
>  - Changed strcmp() ==0 to !strcmp()
>  - Addressed comment from Cornelia Hunk
>  - Merged sysfs Documentation patch with syfs patch
>  - Added more description for alias return value
> v1->v2:
>  - Corrected a typo from 'and' to 'an'
>  - Addressed comments from Alex Williamson
>  - Kept mdev_device naturally aligned
>  - Added error checking for crypt_*() calls
>  - Moved alias NULL check at beginning
>  - Added mdev_alias() API
>  - Updated mtty driver to show example mdev_alias() usage
>  - Changed return type of generate_alias() from int to char*
> v0->v1:
>  - Addressed comments from Alex Williamson, Cornelia Hunk and Mark Bloch
>  - Moved alias length check outside of the parent lock
>  - Moved alias and digest allocation from kvzalloc to kzalloc
>  - &alias[0] changed to alias
>  - alias_length check is nested under get_alias_length callback check
>  - Changed comments to start with an empty line
>  - Added comment where alias memory ownership is handed over to mdev device
>  - Fixed cleaunup of hash if mdev_bus_register() fails
>  - Updated documentation for new sysfs alias file
>  - Improved commit logs to make description more clear
>  - Fixed inclusiong of alias for NULL check
>  - Added ratelimited debug print for sha1 hash collision error
> 
> Parav Pandit (5):
>   mdev: Introduce sha1 based mdev alias
>   mdev: Make mdev alias unique among all mdevs
>   mdev: Expose mdev alias in sysfs tree
>   mdev: Introduce an API mdev_alias
>   mtty: Optionally support mtty alias
> 
>  .../driver-api/vfio-mediated-device.rst       |   9 ++
>  drivers/vfio/mdev/mdev_core.c                 | 142 +++++++++++++++++-
>  drivers/vfio/mdev/mdev_private.h              |   5 +-
>  drivers/vfio/mdev/mdev_sysfs.c                |  26 +++-
>  include/linux/mdev.h                          |   5 +
>  samples/vfio-mdev/mtty.c                      |  13 ++
>  6 files changed, 190 insertions(+), 10 deletions(-)
> 

The patches on their own look sane (and I gave my R-b), but the
consumer of this new API should be ready before this is merged, as
already discussed below.