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Date: Fri, 09 Jun 2017 14:15:37 +0300
From: Felipe Balbi <felipe.balbi@...ux.intel.com>
To: Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>
Cc: Linux USB <linux-usb@...r.kernel.org>,
linux-kernel@...r.kernel.org,
Chunyan Zhang <zhang.chunyan@...aro.org>
Subject: Re: [PATCH] usb: gadget: functions: add ftrace export over USB
Felipe Balbi <felipe.balbi@...ux.intel.com> writes:
> Felipe Balbi <felipe.balbi@...ux.intel.com> writes:
>
>> Allow for ftrace data to be exported over a USB Gadget
>> Controller. With this, we have a potentially very fast pipe for
>> transmitting ftrace data to a Host PC for further analysis.
>>
>> Note that in order to decode the data, one needs access to kernel
>> symbols in order to convert binary data into function names and what
>> not.
>>
>> Signed-off-by: Felipe Balbi <felipe.balbi@...ux.intel.com>
>> ---
>>
>> I wanted to take this through the gadget tree, but there is a
>> dependency with a previous patch of mine adding and extra argument to
>> the ->write() function. Hoping someone else will take it.
>
> just as an extra note here. In order for this to be really useful, it
> would be nice to be able to control what is going to be traced over USB
> as well, but that means exporting a few extra functions to GPL drivers.
>
> Would that be okay? I could have a set of vendor-specific control
> requests to set buffer size and to read/write ftrace filter functions.
>
> The idea is that things like e.g. Android SDK could rely on this on
> debug builds and the SDK itself would make sure to keep a copy of
> vmlinux around to processing of the data coming through USB.
something along these lines (although I think trace buffer size doesn't
matter for trace export, but it serves well enough to illustrate a
point):
modified drivers/usb/gadget/function/f-trace.c
@@ -33,6 +33,8 @@ struct usb_ftrace {
struct usb_ep *in;
+ u32 buffer_size;
+ u16 version;
u8 intf_id;
};
#define ftrace_to_trace(f) (container_of((f), struct usb_ftrace, ftrace))
@@ -40,6 +42,12 @@ struct usb_ftrace {
#define to_trace(f) (container_of((f), struct usb_ftrace, function))
#define FTRACE_REQUEST_QUEUE_LENGTH 250
+#define FTRACE_VERSION 0x0100 /* bcd 1.00 */
+
+/* FTrace vendor-specific requests */
+#define USB_FTRACE_GET_VERSION 0x00
+#define USB_FTRACE_GET_TRACE_BUF_SIZE 0x01
+#define USB_FTRACE_SET_TRACE_BUF_SIZE 0x02
static inline struct usb_request *next_request(struct list_head *list)
{
@@ -142,6 +150,13 @@ static void ftrace_complete(struct usb_ep *ep, struct usb_request *req)
list_move_tail(&req->list, &trace->list);
}
+static void ftrace_set_trace_buf_size_complete(struct usb_ep *ep, struct usb_request *req)
+{
+ struct usb_ftrace *trace = req->context;
+
+ trace_set_buf_size(le32_to_cpu(trace->buffer_size));
+}
+
static void ftrace_queue_work(struct work_struct *work)
{
struct usb_ftrace *trace = work_to_trace(work);
@@ -237,6 +252,71 @@ static int ftrace_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
return -EINVAL;
}
+extern unsigned long trace_get_buf_size(void);
+
+static int ftrace_setup(struct usb_function *f, const struct usb_ctrlrequest *ctrl)
+{
+ struct usb_configuration *c = f->config;
+ struct usb_request *req = c->cdev->req;
+ struct usb_ftrace *trace = to_trace(f);
+
+ int ret;
+
+ u16 index = le16_to_cpu(ctrl->wIndex);
+ u16 value = le16_to_cpu(ctrl->wValue);
+ u16 length = le16_to_cpu(ctrl->wLength);
+
+ if (value != 0 || index != 0)
+ return -EINVAL;
+
+ switch (ctrl->bRequest) {
+ case USB_FTRACE_GET_VERSION:
+ if (ctrl->bRequestType != (USB_DIR_IN | USB_TYPE_VENDOR |
+ USB_RECIP_INTERFACE))
+ return -EINVAL;
+
+ if (length != 2)
+ return -EINVAL;
+
+ req->zero = 0;
+ req->length = 2;
+ req->buf = &trace->version;
+ break;
+ case USB_FTRACE_GET_TRACE_BUF_SIZE:
+ if (ctrl->bRequestType != (USB_DIR_IN | USB_TYPE_VENDOR |
+ USB_RECIP_INTERFACE))
+ return -EINVAL;
+
+ if (length != 2)
+ return -EINVAL;
+
+ trace->buffer_size = cpu_to_le32(trace_get_buf_size());
+
+ req->zero = 0;
+ req->length = 2;
+ req->buf = &trace->buffer_size;
+ break;
+ case USB_FTRACE_SET_TRACE_BUF_SIZE:
+ if (ctrl->bRequestType != (USB_DIR_OUT | USB_TYPE_VENDOR |
+ USB_RECIP_INTERFACE))
+ return -EINVAL;
+
+ if (length != 4)
+ return -EINVAL;
+
+ req->zero = 0;
+ req->length = 4;
+ req->context = trace;
+ req->complete = ftrace_set_trace_buf_size_complete;
+ req->buf = &trace->buffer_size;
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ return usb_ep_queue(c->cdev->gadget->ep0, req, GFP_ATOMIC);
+}
+
static int ftrace_bind(struct usb_configuration *c, struct usb_function *f)
{
struct usb_composite_dev *cdev = c->cdev;
@@ -247,6 +327,8 @@ static int ftrace_bind(struct usb_configuration *c, struct usb_function *f)
int ret;
int i;
+ trace->version = cpu_to_le16(FTRACE_VERSION);
+
us = usb_gstrings_attach(cdev, ftrace_strings,
ARRAY_SIZE(ftrace_string_defs));
if (IS_ERR(us))
modified kernel/trace/trace.c
@@ -618,6 +618,12 @@ int tracing_is_enabled(void)
static unsigned long trace_buf_size = TRACE_BUF_SIZE_DEFAULT;
+unsigned long trace_get_buf_size(void)
+{
+ return trace_buf_size;
+}
+EXPORT_SYMBOL_GPL(trace_get_buf_size);
+
/* trace_types holds a link list of available tracers. */
static struct tracer *trace_types __read_mostly;
--
balbi
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