Re: [PATCH v3 0/3] usb: gadget: 9pfs transport

[Andrzej Pietrasiewicz <andrzej.p@collabora.com>]

Hi Michael,

W dniu 26.02.2024 o 14:56, Michael Grzeschik pisze:
> This series is adding support to mount usb hostside exported 9pfs
> filesystems via the usb gadget interface. It also includes a simple tool
> (p9_fwd.py) to translate an tcp 9pfs transport and reuse it via the usb
> interface.
> 
>      +--------------------------+    |    +--------------------------+
>      |  9PFS mounting client    |    |    |  9PFS exporting server   |
>   SW |                          |    |    |                          |
>      |   (this:trans_usbg)      |    |    |(e.g. diod or nfs-ganesha)|
>      +-------------^------------+    |    +-------------^------------+
>                    |                 |                  |
>                    |                 |           +------v------+
>                    |                 |           |  p9_fwd.py  |
>                    |                 |           +------^------+
>                    |                 |                  |
> ------------------|------------------------------------|-------------
>                    |                 |                  |
>      +-------------v------------+    |    +-------------v------------+
>      |                          |    |    |                          |
>   HW |   USB Device Controller  <--------->   USB Host Controller    |
>      |                          |    |    |                          |
>      +--------------------------+    |    +--------------------------+
> 
> The USB host exports a filesystem, while the gadget on the USB device
> side makes it mountable.
> 
> Diod (9pfs server) and the forwarder are on the development host, where
> the root filesystem is actually stored. The gadget is initialized during
> boot (or later) on the embedded board. Then the forwarder will find it
> on the USB bus and start forwarding requests.
> 
> In this case the 9p requests come from the device and are handled by the
> host. The reason is that USB device ports are normally not available on
> PCs, so a connection in the other direction would not work.
> 
> One use-case is to use it as an alternative to NFS root booting during
> the development of embedded Linux devices.
> 
> Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> ---
> Changes in v3:
> - dropped patch "usb: gadget: legacy: add 9pfs multi gadget" as discussed with gregkh

I will give the dropped patch a try to see how it works, as it should work the
same way regardless of how the gadget is composed, legacy or configfs.

Speaking of the latter, IMO there _are_ valid usecases other than having 9pfs
rootfs, so configfs support should be there. If you intend to send the patches
adding configfs support then kindly Cc me and I will test and review it for you.

Regards,

Andrzej

> - Link to v2: https://lore.kernel.org/r/20240116-ml-topic-u9p-v2-0-b46cbf592962@pengutronix.de
> 
> Changes in v2:
> - improved the commit messages
> - introduced an patch to move the header u_f.h to include/linux/usb to compile usb gadget functions treewide
> - moved usbg gadget function to net/9p/
> - adderessed several comments in function driver, like the cleanup path and kbuild errors
> - improved the documentation in Documentation/filesystems/9p.rst
> - Link to v1: https://lore.kernel.org/r/20240116-ml-topic-u9p-v1-0-ad8c306f9a4e@pengutronix.de
> 
> ---
> Michael Grzeschik (3):
>        usb: gadget: function: move u_f.h to include/linux/usb/
>        net/9p/usbg: Add new usb gadget function transport
>        tools: usb: p9_fwd: add usb gadget packet forwarder script
> 
>   Documentation/filesystems/9p.rst                |  47 ++
>   drivers/usb/gadget/configfs.c                   |   2 +-
>   drivers/usb/gadget/function/f_fs.c              |   2 +-
>   drivers/usb/gadget/function/f_hid.c             |   2 +-
>   drivers/usb/gadget/function/f_loopback.c        |   2 +-
>   drivers/usb/gadget/function/f_midi.c            |   2 +-
>   drivers/usb/gadget/function/f_midi2.c           |   2 +-
>   drivers/usb/gadget/function/f_sourcesink.c      |   2 +-
>   drivers/usb/gadget/u_f.c                        |   2 +-
>   {drivers/usb/gadget => include/linux/usb}/u_f.h |   0
>   net/9p/Kconfig                                  |   6 +
>   net/9p/Makefile                                 |   4 +
>   net/9p/trans_usbg.c                             | 871 ++++++++++++++++++++++++
>   tools/usb/p9_fwd.py                             | 194 ++++++
>   14 files changed, 1130 insertions(+), 8 deletions(-)
> ---
> base-commit: 41bccc98fb7931d63d03f326a746ac4d429c1dd3
> change-id: 20240116-ml-topic-u9p-895274530eb1
> 
> Best regards,