On Fri, Aug 05, 2016 at 01:11:45PM +0200, Nicolai Stange wrote: > Brian Starkey <[email protected]> writes: > > > On Tue, Aug 02, 2016 at 07:31:36PM +0200, Nicolai Stange wrote: > >>Nicolai Stange <[email protected]> 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... > But I also think that it is a little bit fragile in the current state: > how many people actually run the Cocci scripts on their changes? AFAICT, > even the kbuild test robot doesn't do this. And after all, the Cocci > script I provided could very well miss some obfuscated writes to > vma->vm_ops: if they aren't done from ->mmap() themselves, but from some > helper function invoked therein, for example. > > I would personally prefer a hand coded full_proxy_mmap() which WARN()s > if the proxied ->mmap() changes vma->vm_ops: > - this would add an extra safety net > - ->mmap() for debugfs files isn't performance critical > - and lastly, we're already doing something similar to this in > open_proxy_open(). Yes, that would be the best thing to do here. thanks, greg k-h
