[DTrace-devel] [PATCH v5 01/11] libdtrace: Support multiple DTrace handles per process

[Kris Van Hees]

On Fri, Aug 21, 2026 at 05:10:49PM +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 at oracle.com>

Reviewed-by: Kris Van Hees <kris.van.hees at oracle.com>

... with a small change, renaming dt_gmap_done to dt_gmaps_done (which I
should have done rom the beginning), and moving the dt_gmaps_done member
in dtrace_hdl_t at the end of the other booleans rather than putting it at
the very end of the struct.

Thanks for the patch - it certainly fixes a problem I introduced when I
did the BPF port.  Making libdtrace be able to handle multiple instances
again is important!

> ---
>  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;
>  
>  #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 */
>  };
>  
>  /*
> 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;
>  
>  		/* open format file */
> -- 
> 2.43.5
>