> ConfigFS is used to compose a gadget of existing functions.
> As far as I can tell there is no smart card CCID usb function in kernel, so either you need to have your own out-of-tree implementation or implement it in userspace with FunctionFS.
I also could not find a CCID usb function in the kernel so my intention is to implement it in user space with FunctionFS.
> FunctionFS is a specific USB function which forwards most of USB traffic to userspace. FunctionFS can be composed into a gadget with ConfigFS, but, by design, its function directory in ConfigFS is _empty_. In other words, if you
>
> mkdir functions/ffs.ccid
>
> you have empty functions/ffs.ccid. You need to mount corresponding FunctionFS instance (ccid) and provide all the descriptors the way FunctionFS expects it.
I mounted the FunctionFS instance (ccid) by doing
mount -t functionfs ccid /dev/gadget
Note that "/dev/gadget" is not there because of GadgetFS. It is an empty directory. The mount is successful and "ep0" appears in "/dev/gadget". After the mount I start the user space application which writes the descriptors, as the structure "descriptors" listed below, to "/dev/gadget/ep0". The application only writes the interface descriptor, CCID class descriptor and endpoint descriptors.
struct {
struct usb_functionfs_descs_head header;
struct {
struct usb_interface_descriptor intf;
struct ccid_class_descriptor ccid;
struct usb_endpoint_descriptor_no_audio source;
struct usb_endpoint_descriptor_no_audio sink;
} __attribute__((packed)) fs_descs, hs_descs;
} __attribute__((packed)) descriptors;
Then I get the kernel error "invalid length: 54 (descriptor 33)". How should I pass the CCID class descriptor?
Thanks for the help,
Pieter
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