Messages in this thread | | | Date | Fri, 13 Oct 2006 17:09:51 -0700 | From | Joel Becker <> | Subject | Re: [ckrm-tech] [PATCH 0/5] Allow more than PAGESIZE data read in configfs |
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On Fri, Oct 13, 2006 at 04:37:38PM -0700, Matt Helsley wrote: > > Sure it works. You have one per resource group. In > > resource_group_make_object(), you sysfs_mkdir() the sysfs file. There > > That's the easy part. Next we need to make the pid attribute whenever a > new task is created. And delete it when the task dies. And move it > around whenever it changes groups. Is there rename() support in /sys? If > not, would changes to allow rename() be acceptable (I'm worried it would > impact alot of assumptions made in the existing code)?
No, you don't create a pid attribute per task. The sysfs file is literally your large attribute. So, instead of echoing a new pid to "/sys/kernel/config/ckrm/group1/pids", you echo to "/sys/ckrm/group1/pids". To display them all, you just cat "/sys/ckrm/group1/pids". It's exactly like the file you want in configfs, just located in a place where it is allowed.
> Consider that having two very similar (but not symlinked!) trees in > both /sys/ ... /res_group and /sys/kernel/config/res_group could be > rather confusing to userspace programmers and users alike.
Not really. It's not identical (tons of attributes live in the configfs part but not the sysfs part), and it has a clear deliniation of what each does.
> It would be strange because when you rmdir a group > in /sys/kernel/config/res_group... a directory in /sys would also > disappear. Yet you can't mkdir or rmdir the /sys dirs. And to edit the
This is no different than tons of sysfs and procfs functionality today.
> Hmm, that suggests a good point. While some one *can* do that or: > > ATTR=( $(cat /sys/kernel/config/ckrm/myresource/attr) ) > > the space available for environment variables is limited. So attempting > to store a large (What's "large"?) attribute in an environment variable > is a potentially buggy practice. This is a significant problem affecting > large attributes in general.
If you can't do it in sh, it's pretty much out of scope. This is a taste rule I use, because like to shell program. Sure, not the end of the world (not a hard rule, I guess), but worth thinking about.
> There are two parts to the complexity: code complexity and the number > of userspace pieces to deal with. I think that in both of these > categories the OVPA approach is more complex. Here's how I see it:
By your definition, sysfs, configfs, and other fs-style control mechanisms are too complex. We should all just be using ioctl() so that coders and users have only one namespace :-)
> > You're effectively suggesting that a specific attribute type of > > "repeated value of type X". No mixed types, no exploded structures, > > just a "list of this attr" sort of thing. This does fit my personal > > requirement of avoiding a generic, abusable system. > > Exactly.
How do you implement it? Full on seq_file with restrictions (ops->start,stop,next,show)? Some sort of array (how do I placehold where the last read(2) was)? Some sort of linked list (again with the placeholding and locking)? Anything short of seq_file+restrictions would be perhaps binding that traversal, no?
Joel
--
"When I am working on a problem I never think about beauty. I only think about how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." - Buckminster Fuller
Joel Becker Principal Software Developer Oracle E-mail: joel.becker@oracle.com Phone: (650) 506-8127 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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