Re: [PATCH 1/2 v2] tracing/events: provide string with undefinedsize support

[Peter Zijlstra]

On Thu, 2009-04-16 at 22:00 +0200, Frederic Weisbecker wrote:
> Impact: less memory usage for tracing
> 
> This patch provides the support for dynamic size strings on
> event tracing.
> 
> The key concept is to use a structure with an ending char array field of
> undefined size and use such ability to allocate the minimal size on the ring
> buffer to make the entry fit inside as opposite to a fixed length strings with
> upper bound.
> 
> This patch provides one new macro:
> 
> -__ending_string(name, src)
> 
> This one declares the string to the structure inside TP_STRUCT__entry.
> You need to provide the name of the string field and the source that will be
> copied inside.
> Two constraints: only one __ending_string() per TRACE_EVENT can be added and
> it must be the last field to be declared. Hence the __ending prefix.
> 
> This macro will declare the necessary field and will also add the dynamic
> size of the string needed for the ring buffer entry allocation.
> 
> It also support filtering because these strings behave essentially
> like usual fixed length string.

can't we simply do __string(name, src) and output something like:

 struct {
   u16 size;
   char str[0];
 } name;

That would get rid of this __ending_ wart.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/