Add support for specifying DOTNET_DiagnosticPortDefaultPrefix

[xoofx]

Hello, 🙂

I have a case where I'm compiling .NET 8 NativeAOT dyld with EventPipe support that I can load in an existing .NET process. I would like to connect to the diagnostic port of this specific dyld by being able to configure my own prefix for the socket configuration. Currently, the prefix is hardcoded with dotnet-diagnostic at (for MacOS/Linux):

runtime/src/native/eventpipe/ds-ipc-pal-socket.c

Lines 692 to 725 in 8fca0a1

	static
	inline
	bool
	ipc_transport_get_default_name (
	ep_char8_t *name,
	int32_t name_len)
	{
	#ifdef DS_IPC_PAL_AF_UNIX
	#ifndef EP_NO_RT_DEPENDENCY
	return ds_rt_transport_get_default_name (
	name,
	name_len,
	"dotnet-diagnostic",
	ep_rt_current_process_get_id (),
	NULL,
	"socket");
	#elif defined (EP_NO_RT_DEPENDENCY) && defined (FEATURE_CORECLR)
	// generate the default socket name in TMP Path
	const ProcessDescriptor pd = ProcessDescriptor::FromCurrentProcess();
	PAL_GetTransportName(
	name_len,
	name,
	"dotnet-diagnostic",
	pd.m_Pid,
	pd.m_ApplicationGroupId,
	"socket");
	return true;
	#else
	return false;
	#endif
	#else
	return false;
	#endif
	}

I'm proposing to add support for an environment variable DOTNET_DiagnosticPortDefaultPrefix that would allow to configure this prefix name.

If not set, it would default to dotnet-diagnostic.

In general, this prefix could be used to disambiguate more easily these diagnostic ports from the pipe/tmp folders when there are several applications/services running on the same machine.

If accepted, I can make a PR.

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[xoofx]

I would like to connect to the diagnostic port of this specific dyld by being able to configure my own prefix for the socket configuration.

Hm, I thought I had tested this but testing it right now, I don't see my NativeAOT dyld creating a dotnet-diagnostic port file in TMPDIR. 🤔

@jkotas do you happen to know if EventPipe in NativeAOT .NET 8 works for shared libraries? A quick glance at the code tells me that it should, but I might be missing something...

[xoofx]

Oh, ok, I missed the warning on the command line and it refers to #91762 and #88087 so going to follow the other issues to see what is working / not working.

[xoofx]

After checking in #88087 (comment), it seems to work. So I'm quite interested in creating a PR for supporting DOTNET_DiagnosticPortDefaultPrefix.