[PATCH] v4l2: move tracepoints to video_usercopy

[PATCH] v4l2: move tracepoints to video_usercopy

[Hans Verkuil]

The (d)qbuf ioctls were traced in the low-level v4l2 ioctl function. The
trace was outside the serialization lock, so that can affect the usefulness
of the timing. In addition, the __user pointer was expected instead of a
proper kernel pointer.

By moving the tracepoints to video_usercopy we ensure that the trace calls
use the correct kernel pointer, and that it happens right after the ioctl
call to the driver, so certainly inside the serialization lock.

In addition, we only trace if the call was successful.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
---
 drivers/media/v4l2-core/v4l2-dev.c   | 9 ---------
 drivers/media/v4l2-core/v4l2-ioctl.c | 9 +++++++++
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
index 1cc1749..b5aaaac 100644
--- a/drivers/media/v4l2-core/v4l2-dev.c
+++ b/drivers/media/v4l2-core/v4l2-dev.c
@@ -31,10 +31,6 @@
 #include <media/v4l2-device.h>
 #include <media/v4l2-ioctl.h>
 
-
-#define CREATE_TRACE_POINTS
-#include <trace/events/v4l2.h>
-
 #define VIDEO_NUM_DEVICES	256
 #define VIDEO_NAME              "video4linux"
 
@@ -395,11 +391,6 @@ static long v4l2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	} else
 		ret = -ENOTTY;
 
-	if (cmd == VIDIOC_DQBUF)
-		trace_v4l2_dqbuf(vdev->minor, (struct v4l2_buffer *)arg);
-	else if (cmd == VIDIOC_QBUF)
-		trace_v4l2_qbuf(vdev->minor, (struct v4l2_buffer *)arg);
-
 	return ret;
 }
 
diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index 68e6b5e..707aef7 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -28,6 +28,9 @@
 #include <media/v4l2-device.h>
 #include <media/videobuf2-core.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/v4l2.h>
+
 /* Zero out the end of the struct pointed to by p.  Everything after, but
  * not including, the specified field is cleared. */
 #define CLEAR_AFTER_FIELD(p, field) \
@@ -2338,6 +2341,12 @@ video_usercopy(struct file *file, unsigned int cmd, unsigned long arg,
 	err = func(file, cmd, parg);
 	if (err == -ENOIOCTLCMD)
 		err = -ENOTTY;
+	if (err == 0) {
+		if (cmd == VIDIOC_DQBUF)
+			trace_v4l2_dqbuf(video_devdata(file)->minor, parg);
+		else if (cmd == VIDIOC_QBUF)
+			trace_v4l2_qbuf(video_devdata(file)->minor, parg);
+	}
 
 	if (has_array_args) {
 		*kernel_ptr = user_ptr;
-- 
1.8.4.3

Re: [PATCH] v4l2: move tracepoints to video_usercopy

[Wade Farnsworth]

Hans Verkuil wrote:
> The (d)qbuf ioctls were traced in the low-level v4l2 ioctl function. The
> trace was outside the serialization lock, so that can affect the usefulness
> of the timing. In addition, the __user pointer was expected instead of a
> proper kernel pointer.
> 
> By moving the tracepoints to video_usercopy we ensure that the trace calls
> use the correct kernel pointer, and that it happens right after the ioctl
> call to the driver, so certainly inside the serialization lock.
> 
> In addition, we only trace if the call was successful.
> 
> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>

Looks good to me.

Acked-by: Wade Farnsworth <wade_farnsworth@mentor.com>

> ---
>  drivers/media/v4l2-core/v4l2-dev.c   | 9 ---------
>  drivers/media/v4l2-core/v4l2-ioctl.c | 9 +++++++++
>  2 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> index 1cc1749..b5aaaac 100644
> --- a/drivers/media/v4l2-core/v4l2-dev.c
> +++ b/drivers/media/v4l2-core/v4l2-dev.c
> @@ -31,10 +31,6 @@
>  #include <media/v4l2-device.h>
>  #include <media/v4l2-ioctl.h>
>  
> -
> -#define CREATE_TRACE_POINTS
> -#include <trace/events/v4l2.h>
> -
>  #define VIDEO_NUM_DEVICES	256
>  #define VIDEO_NAME              "video4linux"
>  
> @@ -395,11 +391,6 @@ static long v4l2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  	} else
>  		ret = -ENOTTY;
>  
> -	if (cmd == VIDIOC_DQBUF)
> -		trace_v4l2_dqbuf(vdev->minor, (struct v4l2_buffer *)arg);
> -	else if (cmd == VIDIOC_QBUF)
> -		trace_v4l2_qbuf(vdev->minor, (struct v4l2_buffer *)arg);
> -
>  	return ret;
>  }
>  
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 68e6b5e..707aef7 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -28,6 +28,9 @@
>  #include <media/v4l2-device.h>
>  #include <media/videobuf2-core.h>
>  
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/v4l2.h>
> +
>  /* Zero out the end of the struct pointed to by p.  Everything after, but
>   * not including, the specified field is cleared. */
>  #define CLEAR_AFTER_FIELD(p, field) \
> @@ -2338,6 +2341,12 @@ video_usercopy(struct file *file, unsigned int cmd, unsigned long arg,
>  	err = func(file, cmd, parg);
>  	if (err == -ENOIOCTLCMD)
>  		err = -ENOTTY;
> +	if (err == 0) {
> +		if (cmd == VIDIOC_DQBUF)
> +			trace_v4l2_dqbuf(video_devdata(file)->minor, parg);
> +		else if (cmd == VIDIOC_QBUF)
> +			trace_v4l2_qbuf(video_devdata(file)->minor, parg);
> +	}
>  
>  	if (has_array_args) {
>  		*kernel_ptr = user_ptr;


-- 
Wade Farnsworth | Sr. Embedded Linux Dev. Engr.
Mentor Embedded™
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