Messages in this thread | | | Date | Thu, 1 Sep 2016 13:50:39 +0100 | From | Liviu Dudau <> | Subject | Re: [PATCH] debugfs: Add proxy function for the mmap file operation |
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On Thu, Sep 01, 2016 at 08:19:33AM +0200, Greg Kroah-Hartman wrote: > On Wed, Aug 31, 2016 at 04:23:52PM +0100, Liviu Dudau wrote: > > On Wed, Aug 31, 2016 at 03:07:49PM +0200, Greg Kroah-Hartman wrote: > > > On Fri, Aug 05, 2016 at 01:11:45PM +0200, Nicolai Stange wrote: > > > > Brian Starkey <brian.starkey@arm.com> writes: > > > > > > > > > On Tue, Aug 02, 2016 at 07:31:36PM +0200, Nicolai Stange wrote: > > > > >>Nicolai Stange <nicstange@gmail.com> writes: > > > > >>> However, if you wish to have some mmapable debugfs file which *can* go > > > > >>> away, introducing mmap support in the debugfs full proxy is perfectly > > > > >>> valid. But please see below. > > > > >> > > > > >>Assuming that you've got such a use case, please consider resending your > > > > >>patch along with the Cocci script below (and the Coccinelle team CC'ed, > > > > >>of course). If OTOH your mmapable debugfs files are never removed, just > > > > >>drop this message and use debugfs_create_file_unsafe() instead. > > > > > > > > > > So we do have an implementation using this, but it's likely we will > > > > > keep it out-of-tree (it's a stop-gap until we can get a non-debugfs > > > > > implementation of the functionality into mainline). > > > > > > > > > > Do you think it's worth merging this (and your cocci script) anyway to > > > > > save someone else doing the same thing later? > > > > > > > > I personally think that having ->mmap() support in debugfs would be a > > > > good thing to have in general and I expect there to be some further > > > > demand in the future. > > > > > > Ugh, mmap in debugfs, that's funny. And sad... > > > > Yeah. > > > > While our need for the mmap-ing the debugfs entry is at best a temporary > > option and a hack, I would be interested to know what alternatives could > > be used to read a large amount of data that does not need the seq_operations > > API? The out-of-tree proof-of-concept code that we have to interact with > > a memory write engine needs to be able to access the output buffer from > > userspace, but that output buffer is created by the kernel KMS driver. > > What type of debugging do you need this for?
Taking snapshots of a composition scene using the KMS driver for Mali DP.
> > A binary sysfs attribute also might work well for you, on the device > that you are talking to, but if not, yeah, mmap on debugfs will work > just fine, seems to be the best fit.
We felt sysfs gives a whiff of official support for the feature, while in reality is a stop gap until we work out the V4L2 functionality to do the same thing.
Best regards, Liviu
> > thanks, > > greg k-h >
-- ==================== | I would like to | | fix the world, | | but they're not | | giving me the | \ source code! / --------------- ¯\_(ツ)_/¯
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