Re: [PATCH blktests 2/3] common/rc: add _echo() function to trace sysfs attribute writes

[Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

On May 13, 2026 / 10:07, Bart Van Assche wrote:
> On 5/13/26 7:05 AM, Daniel Wagner wrote:
> > On Wed, May 13, 2026 at 08:23:25PM +0900, Shin'ichiro Kawasaki wrote:
> > > +# Echo a value to a file. This wrapper is used to trace sysfs attribute writes
> > > +# when the --cmd-trace option is enabled.
> > > +_echo() {
> > > +	echo "$1" > "$2"
> > > +}
> > 
> > Stupid question, can't we override the echo function, something like this:
> > 
> > echo() {
> >      builtin echo "$@"
> >      builtin echo "$@" >> "/tmp/debug_log.txt"
> > }
> 
> How can this work since the sysfs/debugfs/configfs attribute is not an
> argument of the echo command?

I guess Daniel's idea was to do as follows:

echo() {
     builtin echo "$@"
     builtin echo "$@" >> "${seqres}.cmdtrace"
}

This can capture both the value and the filename in the .cmdtrace file.

Said that, this will not work when printf is used to write to
sysfs/debugfs/configfs attributes. So, I'm tempted to Bart's idea to
rename _echo() to _set_attr().