Read fault when running example network/nfsd-trace.stp stap

[Yun-Chih Chen]

On Wed, May 31, 2017 at 2:44 AM, David Smith <dsmith@redhat.com> wrote:
> Hmm. The good news here is that systemtap is properly exiting here
> instead of accessing that NULL pointer and crashing your system.
>
> Does this work for a while then fail or does it always fail on the
> first read request?

It always fail at the first NFSv3 read request (NFSv4 is okay).

To speed up the tracing, I ended up printing inode number only and get
filename from inode number at post-processing stage:

probe kernel.function("nfsd_vfs_read@fs/nfsd/vfs.c") !,
          module("nfsd").function("nfsd_vfs_read@fs/nfsd/vfs.c") ? {
    i = $file->f_inode;
    inode = @cast(i, "struct inode")->i_ino;
    printf("N %d %d %d\n", gettimeofday_ms(), inode);
}