probe::nfs.proc.read.3stap man page
probe::nfs.proc.read — NFS client synchronously reads file from server
read bytes in this execution
the file offset
IP address of server
used to set task->tk_flags in rpc_init_task function
All the nfs.proc.read kernel functions were removed in kernel commit 8e0969 in December 2006, so these probes do not exist on Linux 2.6.21 and newer kernels.