Re: [RFC 0/2] strace/drm: Add i915 ioctls to strace

[Gabriel Laskar <gabriel@lse.epita.fr>]

On Wed,  6 May 2015 16:48:01 +0200
Patrik Jakobsson <patrik.jakobsson@linux.intel.com> wrote:

> This patch set aims to make strace more useful when tracing i915 ioctls.
> The ioctl type is first checked for being drm and then the driver
> backing the opened device is identified by looking at sysfs. Other
> drivers than i915 can easily be added.
> 
> Only a subset of the i915 ioctls are included. I will extend this patch
> set if the approach looks ok. The generic drm ioctls are also missing.
> 
> Give it a spin with:
>         strace -e trace=ioctl -p `pidof X`
> 
> Patrik Jakobsson (2):
>   strace/drm: Print extended info for drm and i915 ioctls
>   strace/drm: Print args for most common i915 ioctls
> 
>  Makefile.am                |   2 +
>  defs.h                     |   2 +
>  drm.c                      | 104 +++++++++++++++++
>  drm_i915.c                 | 278 +++++++++++++++++++++++++++++++++++++++++++++
>  ioctl.c                    |   5 +
>  xlat/drm_i915_getparams.in |  28 +++++
>  xlat/drm_i915_ioctls.in    |  51 +++++++++
>  xlat/drm_i915_setparams.in |   4 +
>  8 files changed, 474 insertions(+)
>  create mode 100644 drm.c
>  create mode 100644 drm_i915.c
>  create mode 100644 xlat/drm_i915_getparams.in
>  create mode 100644 xlat/drm_i915_ioctls.in
>  create mode 100644 xlat/drm_i915_setparams.in
> 

This is a great start! We need this kind of decoding. Do you plan to
add also the generic drm ioctl decoding?

Some issues though:

* The way you avoid the ioctl request decoding is quite hard to follow,
  but it seems that you don't have much of a choice, except that in
  drm_ioctl(), the code from SYS_FUNC(ioctl) is duplicated. It seems it
  needs some work here, to allow a simpler code path. Maybe this would
  be clearer if the decoding/drm_get_driver_name, etc… was in
  ioctl_decode_command_number(). Also, with the actual code, if you are
  on i915 with an invalid ioctl number, it will be printed as
  "I915_IOCTL_???" and not "_IOC(...)" (see below for an example.) This
  will also add an inconsistent result depending whether /sys is
  mounted or not.
* This does not compile on my system (archlinux), because drm.h lives
  in libdrm/drm.h and not in drm/drm.h, I know it is an rfc, but this
  needs to use pkg-config in order to know where libdrm headers are.


#include <fcntl.h>
#include <sys/ioctl.h>
#include <unistd.h>

#include <drm.h>
#include <i915_drm.h>

int main()
{
	int fd = open("/dev/dri/card0", O_RDWR);
	ioctl(fd, DRM_IOW(DRM_COMMAND_BASE + DRM_I915_FLUSH, int), 0);
	return 0;
}

$ CFLAGS=-I/usr/include/libdrm make i915-ioctls
cc -I/usr/include/libdrm    i915-ioctls.c   -o i915-ioctls
$ sudo strace -e ioctl ./i915-ioctls 
ioctl(3, _IOC(_IOC_WRITE, 0x64, 0x41, 0x04), 0) = 0
+++ exited with 0 +++
$ sudo ~/source/strace/strace -e ioctl ./i915-ioctls 
ioctl(3, 0x40046441 /* I915_IOCTL_??? */, 0) = 0
+++ exited with 0 +++


-- 
Gabriel Laskar
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