On Tue, Jan 18, 2022 at 08:08:49PM +0100, Ingo Rohloff wrote:
> This patch implements the same functionality for USB Gadget FunctionFS as
> commit f7d34b445abc00e979b7 ("USB: Add support for usbfs zerocopy.")
> did for USB host devio.c
>
> This patch allows user space to mmap USB transfer buffers via
> USB FunctionFS endpoint 0.
>
> User space might then use these buffers in conjunction with
> Linux native AsyncIO (via libaio) to avoid data copying by the kernel.
>
> Standard read() and write() operations to bulk USB endpoints will NOT be
> zerocopy. Especially for reads, the expected USB transfer length is
> unclear; whereas an AsyncIO request clearly specifies the maximum transfer
> length.
>
> Signed-off-by: Ingo Rohloff <ingo.rohloff@xxxxxxxxxxxxxx>
> ---
> drivers/usb/gadget/function/f_fs.c | 230 ++++++++++++++++++++++++++++-
> 1 file changed, 226 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index 25ad1e97a458..a8fac065b9b4 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -201,6 +201,16 @@ struct ffs_epfile {
> unsigned char _pad;
> };
>
> +struct ffs_memory {
> + struct list_head memlist;
> + char *kmem;
> + unsigned long vm_start;
> + u32 size;
> +
> + int vma_use_count;
> + int aio_use_count;
> +};
> +
> struct ffs_buffer {
> size_t length;
> char *data;
> @@ -227,6 +237,7 @@ struct ffs_io_data {
> bool use_sg;
>
> struct ffs_data *ffs;
> + struct ffs_memory *ffsm;
> };
>
> struct ffs_desc_helper {
> @@ -262,6 +273,135 @@ static int ffs_mutex_lock(struct mutex *mutex, unsigned nonblock)
> static char *ffs_prepare_buffer(const char __user *buf, size_t len)
> __attribute__((warn_unused_result, nonnull));
>
> +/* Handling of mmapped transfers *******************************/
> +
> +static LIST_HEAD(ffsm_list);
> +static DEFINE_SPINLOCK(ffsm_lock);
> +
> +/* Limit on the total amount of memory ffs can allocate via mmap */
> +static u32 ffsm_memory_mb = 16;
> +module_param(ffsm_memory_mb, uint, 0644);
> +MODULE_PARM_DESC(ffsm_memory_mb,
> + "maximum MB allowed for ffs mmap buffers (0 = no limit)");
No, sorry, this is not the 1990's, we can not add new module parameters
for stuff like this. The code should "just work" without needing to be
tuned.
thanks,
greg k-h
