Re: runtime transport changes

[Tom Zanussi <zanussi at us dot ibm dot com>]

Martin Hunt writes:
 > I've checked in the following changes to stpd and the runtime transport.
 > 
 > 1. Netlink is conpletely removed. It has been replaced with a
 > filesystem-based transport that lives in /proc/systemtap.  This is now
 > the default.
 > 
 > 2. To use relayfs, you define STP_RELAYFS.  See shellsnoop.c for an
 > example.
 > 
 > 3. stp-control.ko is gone.
 > 
 > 4. The "stp" scripts are gone.  Just run "stpd modulename".  stpd will
 > attempt to find a script named "stp_check" to compile and load the
 > relayfs module if it isn't already loaded.  The rpm puts stp_check
 > in /usr/libexec/systemtap, but if you are running a stpd that wasn't
 > built as part of an rpm, it won't know to look there.  Copy it (or link
 > to it) to your path somewhere. The relayfs module will currently get
 > loaded even if it is never used.
 > 
 > 5. Relayfs doesn't work on rawhide kernels, but the new transport works
 > fine.

What you mean is systemtap doesn't work with relayfs on rawhide
kernels, not that relayfs itself doesn't work, right?  I don't know
what version of relayfs is in rawhide, but it should work fine for
anything written to the corresponding API.

I can update the systemtap transport to use whichever API is present
on the target system, but I'm not sure about the best way to do it -
currently we have 3 places to look for relayfs - the relayfs in
systemtap/runtime/relayfs (actually shouldn't this be removed?  Why is
it still there if relayfs is in the kernel?), the relayfs in the RHEL
kernel fs/relayfs, which is the same, and the relayfs in rawhide
fs/relayfs (I'm assuming relayfs is in rawhide) or some other kernel
being used on the system such as rc5-mm1, with the latest relayfs and
API changes.  The only way I know to distinguish which version of
relayfs is being used on the system is to look at
RELAYFS_CHANNEL_VERSION in /include/linux/relayfs_fs.h - for the old
API that will be 3 and for the new > 3.  So I guess I'd need to put a
couple ifdefs with RELAYFS_VERSION > 3 in the transport code, and then
have the build find out from relayfs_fs.h which version to use in the
compilation.  Let me know if you have any other ideas on this.

Thanks,

Tom