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SubjectRe: 2.6.11-rc1-mm1
Christoph Hellwig writes:
> On Fri, Jan 14, 2005 at 04:11:38PM -0500, Karim Yaghmour wrote:
> > Where does this appear in relayfs and what rights do
> > user-space apps have over it (rwx).
>
> Why would you want anything but read access?

This would allow an application to write trace events of its own to a
trace stream for instance. Also, I added a user-requested 'feature'
whereby write()s on a relayfs channel would be sent to a callback that
could be used to interpret 'out-of-band' commands sent from the
userspace application. And if lockless logging were being used, this
could provide a cheaper way for applications to write to the trace
buffer than having to do it via syscall.

>
> > bufsize, nbufs:
> > Usually things have to be subdivided in sub-buffers to make
> > both writing and reading simple. LTT uses this to allow,
> > among other things, random trace access.
>
> I think random access is overkill. Keeping the code simple is more
> important and user-space can post-process it.
>
> > resize_min, resize_max:
> > Allow for dynamic resizing of buffer.
>
> Auto-resizing sounds like a really bad idea.

It also doesn't seem to be really useful to anyone, so we should
probably remove it.

Tom

>
> > init_buf, init_buf_size:
> > Is there an initial buffer containing some data that should
> > be used to initialize the channel's content. If you're doing
> > init-time tracing, for example, you need to have a pre-allocated
> > static buffer that is copied to relayfs once relayfs is mounted.
>
> And why can't you do this from that code? It just needs an initcall-like
> thing that runs after mounting of relayfs.
>

--
Regards,

Tom Zanussi <zanussi@us.ibm.com>
IBM Linux Technology Center/RAS

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