[DTrace-devel] [PATCH 1/2] fbt: Populate just once

[Kris Van Hees]

On Tue, Jan 13, 2026 at 04:42:04PM -0500, eugene.loh at oracle.com wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
> 
> In commit 0b7c5a632 ("fbt, rawfbt: consolidate code to avoid duplication"),
> the populate() functions for fbt and rawfbt were combined, populating both
> providers, but the function was still called twice.  That is, dt_open.c
> tries to insert each provider twice.

Where do you see evidence that the populate function is being called twice?
Only the providers listed in the static initial list have populate() called,
and while &dt_fbt is in that list, &dt_rawfbt is not.  Also, adding debugging
output to populate() in dt_prov_fbt.c (or enabling DTRACE_DEBUG) shows that
it is only called once.

> One solution would be to have a different populate() function for each
> provider.
> 
> Here, we employ another solution:  in dt_provider_create(), check to see
> if a specified provider has already been inserted.

This change is not needed but it is also harmless and can avoid future problems
so I would not object having this as a safety net.

> This also requires a corresponding change in dt_provider_lookup(), so
> that it will work even if no providers have yet been inserted.
> 
> Also, fix a minor comment in the fbt provider.

Thanks for this fix.

> 
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
> ---
>  libdtrace/dt_prov_fbt.c | 2 +-
>  libdtrace/dt_provider.c | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/libdtrace/dt_prov_fbt.c b/libdtrace/dt_prov_fbt.c
> index bbe44a842..3feac56ea 100644
> --- a/libdtrace/dt_prov_fbt.c
> +++ b/libdtrace/dt_prov_fbt.c
> @@ -228,7 +228,7 @@ static int provide(dtrace_hdl_t *dtp, const dtrace_probedesc_t *pdp)
>  		if (!dt_symbol_traceable(sym))
>  			continue;
>  
> -		/* Function name cannot be synthetic and must match. */
> +		/* Function name cannot be synthetic (unless rawfbt) and must match. */
>  		fun = dt_symbol_name(sym);
>  		if ((!rawfbt && strchr(fun, '.')) || !dt_gmatch(fun, pdp->fun))
>  			continue;
> diff --git a/libdtrace/dt_provider.c b/libdtrace/dt_provider.c
> index 848fdc132..9d75225fa 100644
> --- a/libdtrace/dt_provider.c
> +++ b/libdtrace/dt_provider.c
> @@ -114,6 +114,8 @@ dt_provider_lookup(dtrace_hdl_t *dtp, const char *name)
>  		return NULL;
>  
>  	strcpy(tmpl.desc.dtvd_name, name);
> +	if (dtp->dt_provs == NULL)
> +		return NULL;
>  	return dt_htab_lookup(dtp->dt_provs, &tmpl);
>  }
>  
> @@ -124,6 +126,10 @@ dt_provider_create(dtrace_hdl_t *dtp, const char *name,
>  {
>  	dt_provider_t *pvp;
>  
> +	pvp = dt_provider_lookup(dtp, name);
> +	if (pvp)
> +		return pvp;
> +
>  	if ((pvp = dt_zalloc(dtp, sizeof(dt_provider_t))) == NULL)
>  		goto nomem;
>  
> -- 
> 2.47.3
>