[PATCH] t0213: skip ancestry tests under user-mode emulation

[PATCH] t0213: skip ancestry tests under user-mode emulation

[Jamie Magee via GitGitGadget]

From: Jamie Magee <jamie.magee@gmail.com>

The tests added in 3c8c638df6 (t0213: add trace2 cmd_ancestry tests,
2026-02-13) expect the cmd_ancestry event to name "test-tool" and
"git". On Linux those names come from the "comm" field of
/proc/<pid>/stat. Under user-mode emulation (e.g. qemu-user) /proc
reports the emulator ("qemu-riscv64") instead, so the event is still
emitted, the TRACE2_ANCESTRY probe enables the tests, and tests 2-5
fail even though they pass on native riscv64.

Require the probe to see "test-tool" in the ancestry of a test-tool
spawned from test-tool, so the tests skip when the names are unreliable.

Cc: Matthew John Cheetham <mjcheetham@outlook.com>
Signed-off-by: Jamie Magee <jamie.magee@gmail.com>
---
    t0213: skip ancestry tests under user-mode emulation

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2168%2FJamieMagee%2Ft0213-skip-under-emulation-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2168/JamieMagee/t0213-skip-under-emulation-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/2168

 t/t0213-trace2-ancestry.sh | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/t/t0213-trace2-ancestry.sh b/t/t0213-trace2-ancestry.sh
index a2b9536da8..2eb86c1952 100755
--- a/t/t0213-trace2-ancestry.sh
+++ b/t/t0213-trace2-ancestry.sh
@@ -31,12 +31,15 @@ PATH="$TTDIR:$PATH" && export PATH
 # no cmd_ancestry event is emitted.  We detect this at runtime and
 # skip the format-specific tests accordingly.
 
-# Determine if cmd_ancestry is supported on this platform.
+# Enable these tests only when cmd_ancestry reports real process names.
+# The procinfo stub emits no event; under user-mode emulation (e.g.
+# qemu-user) /proc reports the emulator, not the guest. Spawn test-tool
+# from test-tool and require "test-tool" in the child's ancestry.
 test_expect_success 'detect cmd_ancestry support' '
 	test_when_finished "rm -f trace.detect" &&
 	GIT_TRACE2_BRIEF=1 GIT_TRACE2="$(pwd)/trace.detect" \
-		test-tool trace2 001return 0 &&
-	if grep -q "^cmd_ancestry" trace.detect
+		test-tool trace2 004child test-tool trace2 001return 0 &&
+	if grep -q "^cmd_ancestry.*test-tool" trace.detect
 	then
 		test_set_prereq TRACE2_ANCESTRY
 	fi

base-commit: e9019fcafe0040228b8631c30f97ae1adb61bcdc
-- 
gitgitgadget

Re: [PATCH] t0213: skip ancestry tests under user-mode emulation

[Junio C Hamano]

"Jamie Magee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> -# Determine if cmd_ancestry is supported on this platform.
> +# Enable these tests only when cmd_ancestry reports real process names.
> +# The procinfo stub emits no event; under user-mode emulation (e.g.
> +# qemu-user) /proc reports the emulator, not the guest. Spawn test-tool
> +# from test-tool and require "test-tool" in the child's ancestry.

T.r.i.c.k.y. ;-)

>  test_expect_success 'detect cmd_ancestry support' '
>  	test_when_finished "rm -f trace.detect" &&
>  	GIT_TRACE2_BRIEF=1 GIT_TRACE2="$(pwd)/trace.detect" \
> -		test-tool trace2 001return 0 &&
> -	if grep -q "^cmd_ancestry" trace.detect
> +		test-tool trace2 004child test-tool trace2 001return 0 &&
> +	if grep -q "^cmd_ancestry.*test-tool" trace.detect

This will be happy even if "test-tool-trash" that happens to have
"test-tool" as its prefix appears on a cmd_ancestry line (for that
matter, things like "cmd_ancestry-not-quite" that has "cmd_ancestry"
as its prefix would be accepted).  I guess that is OK because we are
testing this in a fairly tightly controlled environment (trace keys
are taken from known vocabulary, not arbitrary strings, for example).

Will queue.  Thanks.

>  	then
>  		test_set_prereq TRACE2_ANCESTRY
>  	fi
>
> base-commit: e9019fcafe0040228b8631c30f97ae1adb61bcdc

Re: [PATCH] t0213: skip ancestry tests under user-mode emulation

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> "Jamie Magee via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>> -# Determine if cmd_ancestry is supported on this platform.
>> +# Enable these tests only when cmd_ancestry reports real process names.
>> +# The procinfo stub emits no event; under user-mode emulation (e.g.
>> +# qemu-user) /proc reports the emulator, not the guest. Spawn test-tool
>> +# from test-tool and require "test-tool" in the child's ancestry.
>
> T.r.i.c.k.y. ;-)
>
>>  test_expect_success 'detect cmd_ancestry support' '
>>  	test_when_finished "rm -f trace.detect" &&
>>  	GIT_TRACE2_BRIEF=1 GIT_TRACE2="$(pwd)/trace.detect" \
>> -		test-tool trace2 001return 0 &&
>> -	if grep -q "^cmd_ancestry" trace.detect
>> +		test-tool trace2 004child test-tool trace2 001return 0 &&
>> +	if grep -q "^cmd_ancestry.*test-tool" trace.detect
>
> This will be happy even if "test-tool-trash" that happens to have
> "test-tool" as its prefix appears on a cmd_ancestry line (for that
> matter, things like "cmd_ancestry-not-quite" that has "cmd_ancestry"
> as its prefix would be accepted).  I guess that is OK because we are
> testing this in a fairly tightly controlled environment (trace keys
> are taken from known vocabulary, not arbitrary strings, for example).
>
> Will queue.  Thanks.

Just to clarify, 'Will queue' simply means that the patch will
appear in 'seen'.  It does not imply that I have personally
reviewed the change and found it acceptable to merge into 'next'.

I would appreciate a review from someone familiar with the trace2
facility.

Thanks.

Re: [PATCH] t0213: skip ancestry tests under user-mode emulation

[Weijie Yuan]

On Mon, Jul 06, 2026 at 05:34:01PM +0000, Jamie Magee via GitGitGadget wrote:
> From: Jamie Magee <jamie.magee@gmail.com>
> 
> The tests added in 3c8c638df6 (t0213: add trace2 cmd_ancestry tests,
> 2026-02-13) expect the cmd_ancestry event to name "test-tool" and
> "git". On Linux those names come from the "comm" field of
> /proc/<pid>/stat. Under user-mode emulation (e.g. qemu-user) /proc
> reports the emulator ("qemu-riscv64") instead, so the event is still
> emitted, the TRACE2_ANCESTRY probe enables the tests, and tests 2-5
> fail even though they pass on native riscv64.
> 
> Require the probe to see "test-tool" in the ancestry of a test-tool
> spawned from test-tool, so the tests skip when the names are unreliable.
> 
> Cc: Matthew John Cheetham <mjcheetham@outlook.com>
> Signed-off-by: Jamie Magee <jamie.magee@gmail.com>
> ---

Very sorry to say something completely outside the patch.

But may I ask what's the point of writting the line started with "Cc:"?
I know that Linux kernel has something about writting Cc in the commit
message, while I don't see much from Git's documentation about trailers,
including MyFirstContribution and SubmittingPatches. Although I know
that "git send-email" and "git interpret-trailers" could use "Cc:", I
still wonder whether using this trailer is encouraged or not. If so,
adding some decriptions about it would be nice, I guess, since I was
confused when reading kernel docs about using Cc trailers in the commit
message sometime ago.

Sorry in advance if I missed any context.

Thanks very much.

Re: [PATCH] t0213: skip ancestry tests under user-mode emulation

[Junio C Hamano]

Weijie Yuan <wy@wyuan.org> writes:

>> ...
>> Cc: Matthew John Cheetham <mjcheetham@outlook.com>
>> Signed-off-by: Jamie Magee <jamie.magee@gmail.com>
>> ---
>
> Very sorry to say something completely outside the patch.
>
> But may I ask what's the point of writting the line started with "Cc:"?
> ...
> I know that Linux kernel has something about writting Cc in the commit
> message, while I don't see much from Git's documentation about trailers,
> including MyFirstContribution and SubmittingPatches.

If you ask me, 'Cc:' belongs in e-mail headers, not in commit
messages, though the Linux kernel community has a different
convention.

GitGitGadget collects 'Cc:' lines from the commit message and, when
sending e-mails on behalf of the author, copies the recipients
listed there, if I am not mistaken.  Thus, it is not surprising that
contributors use the trailer for that purpose.

We do not use the 'Cc:' trailer to allow a commit author to say, "As
the commit object indicates, I CC'd this change to that expert.  I
am no longer solely responsible for any bugs in this commit.  That
expert should have caught my mistake!"  ;-)

Thanks.

Re: [PATCH] t0213: skip ancestry tests under user-mode emulation

[Weijie Yuan]

On Tue, Jul 21, 2026 at 02:55:44PM -0700, Junio C Hamano wrote:
> Weijie Yuan <wy@wyuan.org> writes:
> 
> >> ...
> >> Cc: Matthew John Cheetham <mjcheetham@outlook.com>
> >> Signed-off-by: Jamie Magee <jamie.magee@gmail.com>
> >> ---
> >
> > Very sorry to say something completely outside the patch.
> >
> > But may I ask what's the point of writting the line started with "Cc:"?
> > ...
> > I know that Linux kernel has something about writting Cc in the commit
> > message, while I don't see much from Git's documentation about trailers,
> > including MyFirstContribution and SubmittingPatches.
> 
> If you ask me, 'Cc:' belongs in e-mail headers, not in commit
> messages, though the Linux kernel community has a different
> convention.
> 
> GitGitGadget collects 'Cc:' lines from the commit message and, when
> sending e-mails on behalf of the author, copies the recipients
> listed there, if I am not mistaken.  Thus, it is not surprising that
> contributors use the trailer for that purpose.

Yeah, I noticed that this patch was sent bt GGG. But since he has
already added "Cc" at the end of the commit message, yet in the actual
email header, there is no "Matthew John Cheetham", which was confusing?
This is something I forgot to mention in the previous email, sorry.

I may have to take a closer look at GGG later.

> We do not use the 'Cc:' trailer to allow a commit author to say, "As
> the commit object indicates, I CC'd this change to that expert.  I
> am no longer solely responsible for any bugs in this commit.  That
> expert should have caught my mistake!"  ;-)

;-) I agree!

Thanks!