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SubjectRe: [PATCH] relayfs redux for 2.6.10: lean and mean
On Thu, Jan 20, 2005 at 08:38:25PM -0500, Karim Yaghmour wrote:
> Greg KH wrote:
> > Hm, how about this idea for cutting about 500 more lines from the code:
> >
> > Why not drop the "fs" part of relayfs and just make the code a set of
> > struct file_operations. That way you could have "relayfs-like" files in
> > any ram based file system that is being used. Then, a user could use
> > these fops and assorted interface to create debugfs or even procfs files
> > using this type of interface.
> >
> > As relayfs really is almost the same (conceptually wise) as debugfs as
> > far as concept of what kinds of files will be in there (nothing anyone
> > would ever rely on for normal operations, but for debugging only) this
> > keeps users and developers from having to spread their debugging and
> > instrumenting files from accross two different file systems.
> However this assumes that the users of relayfs are not going to want
> it during normal system operation.

That is true.

> This is an assumption that fails with at least LTT as it is targeted
> at sysadmins, application developers and power users who need to be
> able to trace their systems at any time.

Are they willing to trade off the performance of LTT to get this? I
thought this was being touted as a "when you need to test" type of
thing, not a "run it all the time" type of feature.

> I don't mind piggy-backing off another fs, if it makes sense, but
> unlike debugfs, relayfs is meant for general use, and all files in there
> are of the same type: relay channels for dumping huge amounts of data
> to user-space.

And a driver will never want to have both a relay channel, and a simple
debug output at the same time? You are now requiring them to look for
that data in two different points in the fs.

> It seems to me the target audience and basic idea (relay
> channels only in the fs) are different, but let me know if there's a
> compeling argument for doing this in another way without making it too
> confusing for users of those special "files" (IOW, when this starts
> being used in distros, it'll be more straightforward for users to
> understand if all files in a mounted fs behave a certain way than if
> they have certain "odd" files in certain directories, even if it's
> /proc.)

So, since you are proposing that relayfs be mounted all the time, where
do you want to mount it at? I had to provide a "standard" location for
debugfs for people to be happy with it, and the same issue comes up

Also, why not export your relayfs ops so that someone useing debugfs can
create a relay channel in it, or in any other type of fs they might


greg k-h
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