Re: [PATCH v3 1/7] libdtrace: Support multiple DTrace handles per process

[Kris Van Hees <kris.van.hees@oracle.com>]

On Tue, Jul 21, 2026 at 04:24:45PM +0100, Alan Maguire wrote:
> For use cases like PCP we require multiple DTrace handles
> in a process; to fix this ensure we tie global map creation
> to the handle and also allow BEGIN and END probes to already
> exist.  Later work can capitalize on efficiences like sharing
> kernel type info, but for now this is enough to make multiple
> instances work.
> 
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  libdtrace/dt_bpf.c         | 6 ++----
>  libdtrace/dt_impl.h        | 1 +
>  libdtrace/dt_prov_dtrace.c | 6 +++++-
>  3 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
> index 146a66e3..be8a4229 100644
> --- a/libdtrace/dt_bpf.c
> +++ b/libdtrace/dt_bpf.c
> @@ -25,8 +25,6 @@
>  #include <dt_btf.h>
>  #include <port.h>
> 
> -static boolean_t       dt_gmap_done = 0;
> -
>  #define BPF_CG_LICENSE "GPL";
> 
>  int
> @@ -1076,11 +1074,11 @@ int
>  dt_bpf_gmap_create(dtrace_hdl_t *dtp)
>  {
>         /* If we already created the global maps, return success. */
> -       if (dt_gmap_done)
> +       if (dtp->dt_gmap_done)
>                 return 0;
> 
>         /* Mark global maps creation as completed. */
> -       dt_gmap_done = 1;
> +       dtp->dt_gmap_done = 1;

ACK.

> 
>  #define CREATE_MAP(name) \
>         if (gmap_create_##name(dtp) == -1) \
> diff --git a/libdtrace/dt_impl.h b/libdtrace/dt_impl.h
> index 5282efbd..7db2ba93 100644
> --- a/libdtrace/dt_impl.h
> +++ b/libdtrace/dt_impl.h
> @@ -433,6 +433,7 @@ struct dtrace_hdl {
>         dt_list_t dt_lib_dep_sorted;    /* dependency sorted library list */
>         dt_global_pcap_t dt_pcap; /* global tshark/pcap state */
>         char *dt_freopen_filename; /* filename for freopen() action */
> +       boolean_t dt_gmap_done; /* global map created */

ACK.

>  };
> 
>  /*
> diff --git a/libdtrace/dt_prov_dtrace.c b/libdtrace/dt_prov_dtrace.c
> index 4b788507..8118ab23 100644
> --- a/libdtrace/dt_prov_dtrace.c
> +++ b/libdtrace/dt_prov_dtrace.c
> @@ -243,7 +243,11 @@ static int attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)
>                         close(fd);
>                 }
>                 free(spec);
> -               if (rc == -1)
> +               /*
> +                * Multiple handles in a process mean we may have BEGIN/END
> +                * uprobe events already.
> +                * */
> +               if (rc == -1 && errno != EEXIST)
>                         return -ENOENT;

ACK, but I do wonder whether the use case of multiple handles in a process
may cause trouble when one of those handles tries to remove the uprobe for
BEGIN/END?  This really should have a test case that shows that two handles
can be operative at the same time, and also a test that shows that closing one
while keeping the other open does not stop the second one from seeing its own
END probe firing.  Ideally, it would be two test cases:

 - one that creates handles A and B, and then closes A and checks B still works
 - one that creates handles A and B, and then closes B and checks A still works

> 
>                 /* open format file */
> --
> 2.43.5
> 
> 
>