Re: [RFC 0/4] Introduce drmfs pseudo filesystem for drm subsystem

[sourab gupta <sourab.gupta@intel.com>]

On Mon, 2016-12-05 at 03:06 -0800, Dhingra, Swati wrote:
> From: Swati Dhingra <swati.dhingra@intel.com>
> 
> Currently, we don't have a stable ABI which can be used for the purpose of
> providing output debug/loggging/crc and other such data from DRM.
> The ABI in current use (filesystems, ioctls, et al.) have their own
> constraints and are intended to output a particular type of data.
> Few cases in point:
> sysfs   - stable ABI, but constrained to one textual value per file
> debugfs - unstable ABI, free-for-all
> ioctls  - not as suitable to many single purpose continuous data
>           dumping, we would very quickly run out ioctl space; requires more
>           userspace support than "cat"
> device nodes -  a real possibilty, kernel instantiation is more tricky,
>                 requires udev (+udev.rules) or userspace discovery of the
>                 dynamic major:minor (via sysfs) [mounting a registered
>                 filesystem is easy in comparison]
> netlink - stream based, therefore involves numerous copies.
> 
> Debugfs is the lesser among the evils here, thereby we have grown used to the
> convenience and flexibility in presentation that debugfs gives us
> (including relayfs inodes) that we want some of that hierachy in stable user
> ABI form.
> 
> Due to these limitations, there is a need for a new pseudo filesytem, that
> would act as a stable 'free-for-all' ABI, with the heirarchial structure and
> thus convenience of debugfs. This will be managed by drm, thus named 'drmfs'.
> DRM would register this filesystem to manage a canonical mountpoint, but this
> wouldn't limit everyone to only using that pseudofs underneath.
> 
> This can serve to hold various kinds of output data from Linux DRM subsystems,
> for the files which can't truely fit anywhere else with existing ABI's but
> present so, for the lack of a better place.
> 
> In this patch series, we have introduced a pseudo filesystem named as 'drmfs'
> for now. The filesystem is introduced in the first patch, and the subsequent
> patches make use of the filesystem interfaces, in drm driver, and making them
> available for use by the drm subsystem components, one of which is i915.
> We've moved the location of i915 GuC logs from debugfs to drmfs in the last
> patch. Subsequently, more such files such as pipe_crc, error states, memory
> stats, etc. can be move to this filesystem, if the idea introduced here is
> acceptable per se. The filesystem introduced is being used to house the data
> generated by i915 driver in this patch series, but will hopefully be generic
> enough to provide scope for usage by any other drm subsystem component.
> 
> The patch series is being floated as RFC to gather feedback on the idea and
> infrastructure proposed here and it's suitability to address the specific
> problem statement/use case.
> 
> TODO: Create documentation. Will do so in next version.
> 
> v2: fix the bat failures caused due to missing config check
> 
> v3: Changes made:
>     - Move the location of drmfs from fs/ to drivers/gpu/drm/ (Chris)
>     - Moving config checks to header (Chris,Daniel)
> 
> 
> Sourab Gupta (4):
>   drm: Introduce drmfs pseudo filesystem interfaces
>   drm: Register drmfs filesystem from drm init
>   drm: Create driver specific root directory inside drmfs
>   drm/i915: Creating guc log file in drmfs instead of debugfs
> 
>  drivers/gpu/drm/Kconfig                    |   9 +
>  drivers/gpu/drm/Makefile                   |   1 +
>  drivers/gpu/drm/drm_drv.c                  |  12 +
>  drivers/gpu/drm/drmfs.c                    | 555 +++++++++++++++++++++++++++++
>  drivers/gpu/drm/i915/i915_guc_submission.c |  33 +-
>  include/drm/drm_drv.h                      |   3 +
>  include/drm/drmfs.h                        |  77 ++++
>  include/uapi/linux/magic.h                 |   3 +
>  8 files changed, 672 insertions(+), 21 deletions(-)
>  create mode 100644 drivers/gpu/drm/drmfs.c
>  create mode 100644 include/drm/drmfs.h
> 
> --
> 2.7.4
> 

Hi dri-devel folks,

Any feedback on the proposed drmfs infrastructure being proposed here?

Regards,
Sourab


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