kernel/linux.git/include/uapi/linux/usb/functionfs.h, branch v7.3-rc1

usb: gadget: f_fs: Introduce rw_proxy file descriptors

2026-07-10T13:00:47+00:00

Currently, FunctionFS exposes each USB endpoint as a separate, unidirectional file descriptor (e.g., `ep1` for IN, `ep2` for OUT). While this mirrors the underlying hardware structure, it forces userspace daemons implementing bidirectional protocols to manage multiple file descriptors. When dealing with legacy protocols which require exposing a single, bi-directional fd to userspace, this becomes problematic. This patch introduces the `FUNCTIONFS_RW_PROXY_EPS` UAPI flag. When passed in the descriptor header during initialization, FunctionFS provisions a "rw_proxy" bidirectional file descriptor (e.g., `ep1_rw`) alongside every pair of IN/OUT endpoints. Implementation details: - RW proxy files act as a pure VFS alias, proxying operations directly to the base ffs_epfile instances. A `read()` proxies to the OUT endpoint's file, and a `write()` proxies to the IN file. - Because operations are proxied natively, they reuse the underlying base endpoint's lock (`epfile->mutex`) and tracking state. This serializes concurrent I/O, preventing buffer corruption or races even if userspace mixes transfers across both the rw_proxy and base files while allowing full-duplex synchronous operations to occur concurrently without serializing on a single lock. - Control operations (like IOCTLs) and intentional stalls (via reverse-direction I/O) must still be issued on the base endpoints, as the rw_proxy returns `-ENOTTY` for IOCTLs and cannot trigger stalls. Assisted-by: Antigravity:gemini-3.1-pro Signed-off-by: Neill Kapron Link: https://patch.msgid.link/20260619040609.4010746-5-nkapron@google.com Signed-off-by: Greg Kroah-Hartman

usb: gadget: f_fs: Add zero-length packet ioctl

2026-07-10T13:00:45+00:00

When transferring data from a USB gadget to a host, a transfer is considered complete when the host receives a short packet (a packet smaller than wMaxPacketSize). If the total transfer length is an exact multiple of wMaxPacketSize, a Zero-Length Packet (ZLP) must be appended to signal the end of the transfer. FunctionFS currently provides no mechanism for userspace to instruct the kernel to set the `req->zero` flag on transfers. Userspace workarounds, such as manually submitting separate 0-byte requests, may not be available for legacy protocols which must maintain write behavior compatibility when moved to functionfs implementations. To resolve this, introduce a new ioctl, FUNCTIONFS_ENDPOINT_ENABLE_ZLP, which takes a pointer to a __u32 flag. When enabled, all subsequent transfers on that endpoint will have the `req->zero` flag set, allowing the underlying USB Device Controller (UDC) hardware to automatically append a ZLP only when mathematically required. For logical transfers chunked across multiple requests, userspace can dynamically toggle this flag, enabling it only prior to submitting the final chunk. The flag defaults to false to maintain backward compatibility. Once enabled, the state is persistent for the lifetime of the endpoint and will not be reset by opening or closing the endpoint file descriptors. Assisted-by: Gemini-CLI:gemini-3.1-pro-preview Signed-off-by: Neill Kapron Link: https://patch.msgid.link/20260619040609.4010746-4-nkapron@google.com Signed-off-by: Greg Kroah-Hartman

usb: gadget: functionfs: fix spellos

2024-12-04T15:08:34+00:00

Fix typos in documentation as reported by codespell. Fixes: f0175ab51993 ("usb: gadget: f_fs: OS descriptors support") Fixes: ddf8abd25994 ("USB: f_fs: the FunctionFS driver") Signed-off-by: Randy Dunlap Cc: Michal Nazarewicz Cc: Andrzej Pietrasiewicz Cc: Greg Kroah-Hartman Cc: linux-usb@vger.kernel.org Link: https://lore.kernel.org/r/20241128033756.373517-1-rdunlap@infradead.org Signed-off-by: Greg Kroah-Hartman

usb: gadget: f_fs: add capability for dfu functional descriptor

2024-08-13T08:38:46+00:00

Add the ability for the USB FunctionFS (FFS) gadget driver to be able to create Device Firmware Upgrade (DFU) functional descriptors. [1] This patch allows implementation of DFU in userspace using the FFS gadget. The DFU protocol uses the control pipe (ep0) for all messaging so only the addition of the DFU functional descriptor is needed in the kernel driver. The DFU functional descriptor is written to the ep0 file along with any other descriptors during FFS setup. DFU requires an interface descriptor followed by the DFU functional descriptor. This patch includes documentation of the added descriptor for DFU and conversion of some existing documentation to kernel-doc format so that it can be included in the generated docs. An implementation of DFU 1.1 that implements just the runtime descriptor using the FunctionFS gadget (with rebooting into u-boot for DFU mode) has been tested on an i.MX8 Nano. An implementation of DFU 1.1 that implements both runtime and DFU mode using the FunctionFS gadget has been tested on Xilinx Zynq UltraScale+. Note that for the best performance of firmware update file transfers, the userspace program should respond as quick as possible to the setup packets. [1] https://www.usb.org/sites/default/files/DFU_1.1.pdf Signed-off-by: David Sands Co-developed-by: Chris Wulff Signed-off-by: Chris Wulff Link: https://lore.kernel.org/r/20240811000004.1395888-2-crwulff@gmail.com Signed-off-by: Greg Kroah-Hartman

usb: gadget: functionfs: Add DMABUF import interface

2024-02-17T16:00:09+00:00

This patch introduces three new ioctls. They all should be called on a data endpoint (ie. not ep0). They are: - FUNCTIONFS_DMABUF_ATTACH, which takes the file descriptor of a DMABUF object to attach to the endpoint. - FUNCTIONFS_DMABUF_DETACH, which takes the file descriptor of the DMABUF to detach from the endpoint. Note that closing the endpoint's file descriptor will automatically detach all attached DMABUFs. - FUNCTIONFS_DMABUF_TRANSFER, which requests a data transfer from / to the given DMABUF. Its argument is a structure that packs the DMABUF's file descriptor, the size in bytes to transfer (which should generally be set to the size of the DMABUF), and a 'flags' field which is unused for now. Before this ioctl can be used, the related DMABUF must be attached with FUNCTIONFS_DMABUF_ATTACH. These three ioctls enable the FunctionFS code to transfer data between the USB stack and a DMABUF object, which can be provided by a driver from a completely different subsystem, in a zero-copy fashion. Signed-off-by: Paul Cercueil Acked-by: Daniel Vetter Acked-by: Christian König Link: https://lore.kernel.org/r/20240130122340.54813-4-paul@crapouillou.net Signed-off-by: Greg Kroah-Hartman

usb: gadget: f_fs: fix fortify warning

2023-12-15T12:55:45+00:00

When compiling with gcc version 14.0.0 20231206 (experimental) and CONFIG_FORTIFY_SOURCE=y, I've noticed the following warning: ... In function 'fortify_memcpy_chk', inlined from '__ffs_func_bind_do_os_desc' at drivers/usb/gadget/function/f_fs.c:2934:3: ./include/linux/fortify-string.h:588:25: warning: call to '__read_overflow2_field' declared with attribute warning: detected read beyond size of field (2nd parameter); maybe use struct_group()? [-Wattribute-warning] 588 | __read_overflow2_field(q_size_field, size); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This call to 'memcpy()' is interpreted as an attempt to copy both 'CompatibleID' and 'SubCompatibleID' of 'struct usb_ext_compat_desc' from an address of the first one, which causes an overread warning. Since we actually want to copy both of them at once, use the convenient 'struct_group()' and 'sizeof_field()' here. Signed-off-by: Dmitry Antipov Link: https://lore.kernel.org/r/20231214090428.27292-1-dmantipov@yandex.ru Signed-off-by: Greg Kroah-Hartman

License cleanup: add SPDX license identifier to uapi header files with no license

2017-11-02T10:19:54+00:00

Many user space API headers are missing licensing information, which makes it hard for compliance tools to determine the correct license. By default are files without license information under the default license of the kernel, which is GPLV2. Marking them GPLV2 would exclude them from being included in non GPLV2 code, which is obviously not intended. The user space API headers fall under the syscall exception which is in the kernels COPYING file: NOTE! This copyright does *not* cover user programs that use kernel services by normal system calls - this is merely considered normal use of the kernel, and does *not* fall under the heading of "derived work". otherwise syscall usage would not be possible. Update the files which contain no license information with an SPDX license identifier. The chosen identifier is 'GPL-2.0 WITH Linux-syscall-note' which is the officially assigned identifier for the Linux syscall exception. SPDX license identifiers are a legally binding shorthand, which can be used instead of the full boiler plate text. This patch is based on work done by Thomas Gleixner and Kate Stewart and Philippe Ombredanne. See the previous patch in this series for the methodology of how this patch was researched. Reviewed-by: Kate Stewart Reviewed-by: Philippe Ombredanne Reviewed-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

usb: gadget: function: f_fs: Let ffs_epfile_ioctl wait for enable.

2017-06-02T08:22:31+00:00

This allows users to make an ioctl call as the first action on a connection. Ex, some functions might want to get endpoint size before making any i/os. Previously, calling ioctls before read/write would depending on the timing of endpoints being enabled. ESHUTDOWN is now a possible return value and ENODEV is not, so change docs accordingly. Acked-by: Michal Nazarewicz Signed-off-by: Jerry Zhang Signed-off-by: Felipe Balbi

usb: gadget: f_fs: Fix ExtCompat documentation in uapi header

2017-04-11T07:58:16+00:00

The code was fixed in commit 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on reserved1 wof OS_DESC_EXT_COMPAT") but the in-header documentation kept referencing 0 as the expected value. Reference 1 instead as per original commit message. Signed-off-by: Vincent Pelletier Signed-off-by: Felipe Balbi

usb: gadget: f_fs: Document eventfd effect on descriptor format.

2017-01-02T08:55:28+00:00

When FUNCTIONFS_EVENTFD flag is set, __ffs_data_got_descs reads a 32bits, little-endian value right after the fixed structure header, and passes it to eventfd_ctx_fdget. Document this. Also, rephrase a comment to be affirmative about the role of string descriptor at index 0. Ref: USB 2.0 spec paragraph "9.6.7 String", and also checked to still be current in USB 3.0 spec paragraph "9.6.9 String". Signed-off-by: Vincent Pelletier Signed-off-by: Felipe Balbi