Re: [PATCH 08/15] tracing: Introduce names for ring buffers

[Alexander Graf]

Hi Steve,

On 13.12.23 01:15, Steven Rostedt wrote:
> On Wed, 13 Dec 2023 00:04:45 +0000
> Alexander Graf <graf@xxxxxxxxxx> wrote:
>
> > With KHO (Kexec HandOver), we want to preserve trace buffers across
> > kexec. To carry over their state between kernels, the kernel needs a
> > common handle for them that exists on both sides. As handle we introduce
> > names for ring buffers. In a follow-up patch, the kernel can then use
> > these names to recover buffer contents for specific ring buffers.
> Is there a way to use the trace_array name instead?
>
> The trace_array is the structure that represents each tracing instance. And
> it already has a name field. And if you can get the associated ring buffer
> from that too.
>
> struct trace_array *tr;
>
>          tr->array_buffer.buffer
>
>          tr->name
>
> When you do: mkdir /sys/kernel/tracing/instance/foo
>
> You create a new trace_array instance where tr->name = "foo" and allocates
> the buffer for it as well.

The name in the ring buffer is pretty much just a copy of the trace 
array name. I use it to reconstruct which buffer we're actually 
referring to inside __ring_buffer_alloc().

I'm all ears for alternative suggestions. I suppose we could pass tr as 
argument to ring_buffer_alloc() instead of the name?


Alex




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