[DTrace-devel] [PATCH 20/38] Add a hook for a provider-specific "update" function

[Kris Van Hees]

This patch surely should be part of another one that actually provides some
code to use the new callback.  The implementation of the callback in any
particular provider could remain in its own patch after that if you like,
but adding this without the code that actually calls it seems less useful.
If anything, the commit message itself makes it so generic sounding that one
is likely to have no idea what this is meant to be used for, where it would
be called from, why, and what the expected result ought to be.

So, combine with the code that uses it please.  Which I will review next :)

On Thu, Jun 27, 2024 at 01:38:46AM -0400, eugene.loh at oracle.com wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
> 
> For up-coming USDT-probe support, we need to update a BPF map
> -- at least when the dtrace session starts but possibly also later
> to support systemwide USDT tracing for processes that may start up
> later.
> 
> One way to do this is with a USDT-specific update function.
> 
> For now, let's add a hook for providers to have provider-specific
> update functions.  User space can either call
> 
>     for (i = 0; i < ARRAY_SIZE(dt_providers); i++) {
>         if (dt_providers[i]->update)
>             dt_providers[i]->update(...);
>     }
> 
> any time it likes.  Or it can call dt_usdt.update(...).
> 
> This is for WIP.  A different approach can be adopted later instead.
> 
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
> ---
>  libdtrace/dt_provider.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/libdtrace/dt_provider.h b/libdtrace/dt_provider.h
> index b1b1b1b8..71b5a3c4 100644
> --- a/libdtrace/dt_provider.h
> +++ b/libdtrace/dt_provider.h
> @@ -71,6 +71,8 @@ typedef struct dt_provimpl {
>  			      void *datap);
>  	void (*destroy)(dtrace_hdl_t *dtp,	/* free provider data */
>  			      void *datap);
> +	void (*update)(dtrace_hdl_t *dtp,	/* update provider-specific info */
> +			      void *datap);
>  } dt_provimpl_t;
>  
>  /* list dt_dtrace first */
> -- 
> 2.18.4
>