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From: Steven Rostedt <rostedt@goodmis.org>
To: "Yordan Karadzhov (VMware)" <y.karadz@gmail.com>
Cc: linux-trace-devel@vger.kernel.org
Subject: Re: [PATCH v2 10/20] kernel-shark: Start using data streams
Date: Thu, 5 Nov 2020 13:17:35 -0500
Message-ID: <20201105131735.3d559bce@gandalf.local.home> (raw)
In-Reply-To: <b5569725-239f-3e5b-dfa0-97f7d51b5d01@gmail.com>

On Thu, 5 Nov 2020 16:58:51 +0200
"Yordan Karadzhov (VMware)" <y.karadz@gmail.com> wrote:

> I see the problem. This is definitely wrong.
> 
> What if in addition to "n_streams" I add another counter called 
> "last_stream_added" and initialize this counter to -1?
> 
> Then I can add streams like this:
> 
> 	kshark_ctx->stream[++kshark_ctx->last_stream_added] = stream;
> 	++kshark_ctx->n_streams;
> 
> > You may want to do instead:

I'm thinking of doing something like this:

struct kshark_ctx {
	[..]
	unsigned int free_stream;
	[..]
};


	if (kshark_ctx->free_stream >= kshark_ctx->n_streams) {
		kshark_ctx->stream[++kshark_ctx->n_streams] = stream;
		kshark_ctx->free_stream = kshark_ctx->n_streams;

/* BTW, the stream array should be allocated to the n_streams, and
   reallocated when it grows.  I don't think we want a huge stream array to
   handle all the bits when not used. */

	} else {
		int new_stream = kshark_ctx->free_stream;

		kshark_ctx->free_stream = kshark_index(kshark_ctx->stream[new_stream]);
		kshark_ctx->stream[new_stream] = stream;
	}


For freeing (index i):

	kshark_ctx->stream[i] = kshark_ptr(kshark_ctx->free_stream);
	kshark_ctx->free_stream = i;


We could define the following (note, I just used these names for the
functions, they could be named something else):


#define KSHARK_INDEX_MASK ((1 << NR_OF_BITS_FOR_STREAM) - 1)

#define KSHARK_INVALID_STREAM (~((1UL << NR_OF_BITS_FOR_STREAM) - 1))

static inline int kshark_index(void *ptr)
{
	unsigned long index = (unsigned long)ptr;

	return (int)(index & KSHARK_INDEX_MASK);
}

static inline void *kshark_ptr(unsigned int index)
{
	unsigned long p;

	p = KSHARK_INVALID_STREAM | index;

	return (void *)p;
}

The KSHARK_INVALID_STREAM and KSHARK_INDEX_MASK, would allow us to do
something like this if we wanted to loop through all streams:

static inline bool kshark_is_valid_stream(void *ptr)
{
	unsigned long p = (unsigned long)ptr;

	return (p & KSHARK_INVALID_STREAM) == KSHARK_INVALID_STREAM;
}

The above works because the address of setting all those bits, would put
the address into the kernel space (illegal user space address).


	for (i = 0; i < kshark_ctx->n_streams; i++) {
		if (!kshark_is_valid_stream(kshark_ctx->stream[i]))
			continue;
		/* process valid stream */
	}

-- Steve

  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-12 13:35 [PATCH v2 00/20] Start KernelShark v2 transformation Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 01/20] kernel-shark: Start introducing KernelShark 2.0 Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 02/20] kernel-shark: Use only signed types in kshark_entry Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 03/20] kernel-shark: Introduce libkshark-hash Yordan Karadzhov (VMware)
2020-10-12 14:05   ` Steven Rostedt
2020-10-12 14:05     ` Steven Rostedt
2020-10-12 14:18       ` Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 04/20] kernel-shark: Introduce Data streams Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 05/20] kernel-shark: Add stream_id to kshark_entry Yordan Karadzhov (VMware)
2020-10-13  0:05   ` Steven Rostedt
2020-10-29 10:08     ` Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 06/20] kernel-shark: Rename static methods in libkshark Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 07/20] kernel-shark: Add basic methods for Data streams Yordan Karadzhov (VMware)
2020-10-13  0:18   ` Steven Rostedt
2020-10-29 10:10     ` Yordan Karadzhov (VMware)
2020-10-29 14:04       ` Steven Rostedt
2020-10-29 14:49         ` Yordan Karadzhov (VMware)
2020-10-30  1:57           ` Steven Rostedt
2020-11-03 13:38             ` Yordan Karadzhov (VMware)
2020-11-04 15:41               ` Steven Rostedt
2020-11-05 14:35                 ` Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 08/20] kernel-shark: Housekeeping before implementing stream interface Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 09/20] kernel-shark: Add stream interface for trace-cmd data Yordan Karadzhov (VMware)
2020-10-13  0:44   ` Steven Rostedt
2020-10-29 11:16     ` Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 10/20] kernel-shark: Start using data streams Yordan Karadzhov (VMware)
2020-10-14 18:56   ` Steven Rostedt
2020-11-05 14:58     ` Yordan Karadzhov (VMware)
2020-11-05 18:17       ` Steven Rostedt [this message]
2020-11-06 14:31         ` Yordan Karadzhov (VMware)
2020-11-06 15:18           ` Steven Rostedt
2020-11-09 14:49             ` Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 11/20] kernel-shark: Remove dead code Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 12/20] kernel-shark: Redesign the plugin interface Yordan Karadzhov (VMware)
2020-10-14 21:09   ` Steven Rostedt
2020-10-12 13:35 ` [PATCH v2 13/20] kernel-shark: Complete the stream integration Yordan Karadzhov (VMware)
2020-10-14 23:52   ` Steven Rostedt
2020-10-12 13:35 ` [PATCH v2 14/20] kernel-shark: Provide merging of multiple data streams Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 15/20] kernel-shark: Integrate the stream definitions with data model Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 16/20] kernel-shark: Use only signed types for model defs Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 17/20] kernel-shark: Add ksmodel_get_bin() Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 18/20] kernel-shark: Protect ksmodel_set_in_range_bining() Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 19/20] kernel-shark: Add methods for time calibration Yordan Karadzhov (VMware)
2020-10-12 13:35 ` [PATCH v2 20/20] kernel-shark: Integrate streams with libkshark-configio Yordan Karadzhov (VMware)
2020-11-05 19:22   ` Steven Rostedt
2020-11-09 14:55     ` Yordan Karadzhov (VMware)
2020-11-09 15:28       ` Steven Rostedt

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