This is better than printing random bytes in the terminal.

Note Jakub suggested 'hexdump', but Mat found out that this tool is not
often installed by default. 'od' can do a similar job, and it is in the
POSIX specs and available in coreutils, so it should be on more systems.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Suggested-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
v2: switch to 'od', and no more check for its presence (Mat)
---
 tools/testing/selftests/net/mptcp/mptcp_lib.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_lib.sh b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
index 09cd24b2ae466205dacbdf8289eb86c08534c475..d62e653d48b0f2ef7a01e289fa0be8907825667d 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
@@ -384,7 +384,7 @@ mptcp_lib_make_file() {
 mptcp_lib_print_file_err() {
 	ls -l "${1}" 1>&2
 	echo "Trailing bytes are: "
-	tail -c 27 "${1}"
+	tail -c 32 "${1}" | od -x | head -n2
 }
 
 # $1: input file ; $2: output file ; $3: what kind of file

-- 
2.51.0

On Fri, 2025-09-05 at 20:18 +0200, Matthieu Baerts (NGI0) wrote:
> This is better than printing random bytes in the terminal.
> 
> Note Jakub suggested 'hexdump', but Mat found out that this tool is
> not
> often installed by default. 'od' can do a similar job, and it is in
> the
> POSIX specs and available in coreutils, so it should be on more
> systems.
> 
> Suggested-by: Jakub Kicinski <kuba@kernel.org>
> Suggested-by: Mat Martineau <martineau@kernel.org>
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> ---
> v2: switch to 'od', and no more check for its presence (Mat)
> ---
>  tools/testing/selftests/net/mptcp/mptcp_lib.sh | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
> b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
> index
> 09cd24b2ae466205dacbdf8289eb86c08534c475..d62e653d48b0f2ef7a01e289fa0
> be8907825667d 100644
> --- a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
> +++ b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
> @@ -384,7 +384,7 @@ mptcp_lib_make_file() {
>  mptcp_lib_print_file_err() {
>  	ls -l "${1}" 1>&2
>  	echo "Trailing bytes are: "
> -	tail -c 27 "${1}"
> +	tail -c 32 "${1}" | od -x | head -n2

nit:

It shows more bytes (32) here, but it wasn't mentioned in the commit
log.

Thanks,
-Geliang

>  }
>  
>  # $1: input file ; $2: output file ; $3: what kind of file

Hi Geliang,

On 06/09/2025 01:42, Geliang Tang wrote:
> On Fri, 2025-09-05 at 20:18 +0200, Matthieu Baerts (NGI0) wrote:
>> This is better than printing random bytes in the terminal.
>>
>> Note Jakub suggested 'hexdump', but Mat found out that this tool is
>> not
>> often installed by default. 'od' can do a similar job, and it is in
>> the
>> POSIX specs and available in coreutils, so it should be on more
>> systems.
>>
>> Suggested-by: Jakub Kicinski <kuba@kernel.org>
>> Suggested-by: Mat Martineau <martineau@kernel.org>
>> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
>> ---
>> v2: switch to 'od', and no more check for its presence (Mat)
>> ---
>>  tools/testing/selftests/net/mptcp/mptcp_lib.sh | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
>> b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
>> index
>> 09cd24b2ae466205dacbdf8289eb86c08534c475..d62e653d48b0f2ef7a01e289fa0
>> be8907825667d 100644
>> --- a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
>> +++ b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
>> @@ -384,7 +384,7 @@ mptcp_lib_make_file() {
>>  mptcp_lib_print_file_err() {
>>  	ls -l "${1}" 1>&2
>>  	echo "Trailing bytes are: "
>> -	tail -c 27 "${1}"
>> +	tail -c 32 "${1}" | od -x | head -n2
> 
> nit:
> 
> It shows more bytes (32) here, but it wasn't mentioned in the commit
> log.

Good point, I can add this when applying the patches:

  Show a few more bytes, just to fill in the two lines.

Would that be OK?

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.

Hi Matt,

On Sat, 2025-09-06 at 15:56 +0200, Matthieu Baerts wrote:
> Hi Geliang,
> 
> On 06/09/2025 01:42, Geliang Tang wrote:
> > On Fri, 2025-09-05 at 20:18 +0200, Matthieu Baerts (NGI0) wrote:
> > > This is better than printing random bytes in the terminal.
> > > 
> > > Note Jakub suggested 'hexdump', but Mat found out that this tool
> > > is
> > > not
> > > often installed by default. 'od' can do a similar job, and it is
> > > in
> > > the
> > > POSIX specs and available in coreutils, so it should be on more
> > > systems.
> > > 
> > > Suggested-by: Jakub Kicinski <kuba@kernel.org>
> > > Suggested-by: Mat Martineau <martineau@kernel.org>
> > > Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> > > ---
> > > v2: switch to 'od', and no more check for its presence (Mat)
> > > ---
> > >  tools/testing/selftests/net/mptcp/mptcp_lib.sh | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
> > > b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
> > > index
> > > 09cd24b2ae466205dacbdf8289eb86c08534c475..d62e653d48b0f2ef7a01e28
> > > 9fa0
> > > be8907825667d 100644
> > > --- a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
> > > +++ b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
> > > @@ -384,7 +384,7 @@ mptcp_lib_make_file() {
> > >  mptcp_lib_print_file_err() {
> > >  	ls -l "${1}" 1>&2
> > >  	echo "Trailing bytes are: "
> > > -	tail -c 27 "${1}"
> > > +	tail -c 32 "${1}" | od -x | head -n2
> > 
> > nit:
> > 
> > It shows more bytes (32) here, but it wasn't mentioned in the
> > commit
> > log.
> 
> Good point, I can add this when applying the patches:
> 
>   Show a few more bytes, just to fill in the two lines.
> 
> Would that be OK?

That would be great.

Thanks,
-Geliang

> 
> Cheers,
> Matt