linux-kernel - [PATCH v2] USB: gadget: udc: tracing: Do not open code __string() with __dynamic

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Date:   Sun, 3 Jul 2022 09:14:49 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org
Subject: [PATCH v2] USB: gadget: udc: tracing: Do not open code __string()
 with __dynamic_array()

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

The event classes udc_log_ep and udc_log_req both declare:

    __dynamic_array(char, name, UDC_TRACE_STR_MAX)

Which will reserve UDC_TRACE_STR_MAX bytes on the ring buffer for the
event to write in name. It then uses snprintf() to write into that space.

Assuming that the string being copied is nul terminated, it is better to
just use the __string() helper. That way only the size of the string is
saved into the ring buffer and not the max size (yes, the entire
UDC_TRACE_STR_MAX is used in the trace event, and anything not used is
just junk in the ring buffer). Worse, there's also meta data saved into
the event that denotes where the string is stored in the event and also
saves its size, which is always going to be UDC_TRACE_STR_MAX.

Convert both to use the __string() and __assign_str() helpers that are for
this kind of use case.

Cc: Felipe Balbi <balbi@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-usb@...r.kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
Changes since v1: Link: https://lkml.kernel.org/r/20220702200127.399d2358@gandalf.local.home
  - Commit the fix to the extra semicolon that I found compiling
    the code, but forgot to do a commit --amend before sending.

 drivers/usb/gadget/udc/trace.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/udc/trace.h b/drivers/usb/gadget/udc/trace.h
index 98584f6b6c66..abdbcb1bacb0 100644
--- a/drivers/usb/gadget/udc/trace.h
+++ b/drivers/usb/gadget/udc/trace.h
@@ -140,7 +140,7 @@ DECLARE_EVENT_CLASS(udc_log_ep,
 	TP_PROTO(struct usb_ep *ep, int ret),
 	TP_ARGS(ep, ret),
 	TP_STRUCT__entry(
-		__dynamic_array(char, name, UDC_TRACE_STR_MAX)
+		__string(name, ep->name)
 		__field(unsigned, maxpacket)
 		__field(unsigned, maxpacket_limit)
 		__field(unsigned, max_streams)
@@ -152,7 +152,7 @@ DECLARE_EVENT_CLASS(udc_log_ep,
 		__field(int, ret)
 	),
 	TP_fast_assign(
-		snprintf(__get_str(name), UDC_TRACE_STR_MAX, "%s", ep->name);
+		__assign_str(name, ep->name);
 		__entry->maxpacket = ep->maxpacket;
 		__entry->maxpacket_limit = ep->maxpacket_limit;
 		__entry->max_streams = ep->max_streams;
@@ -214,7 +214,7 @@ DECLARE_EVENT_CLASS(udc_log_req,
 	TP_PROTO(struct usb_ep *ep, struct usb_request *req, int ret),
 	TP_ARGS(ep, req, ret),
 	TP_STRUCT__entry(
-		__dynamic_array(char, name, UDC_TRACE_STR_MAX)
+		__string(name, ep->name)
 		__field(unsigned, length)
 		__field(unsigned, actual)
 		__field(unsigned, num_sgs)
@@ -228,7 +228,7 @@ DECLARE_EVENT_CLASS(udc_log_req,
 		__field(struct usb_request *, req)
 	),
 	TP_fast_assign(
-		snprintf(__get_str(name), UDC_TRACE_STR_MAX, "%s", ep->name);
+		__assign_str(name, ep->name);
 		__entry->length = req->length;
 		__entry->actual = req->actual;
 		__entry->num_sgs = req->num_sgs;
-- 
2.35.1