Hi Eric:

thanks for your review.

On 10/31/2015 01:36 AM, Eric Blake wrote:
> On 10/30/2015 01:13 AM, Bo Tu wrote:
>> Be easier to read, and be slightly shorter.
> You mentioned a very short "what" in the subject line (good), but the
> "why" in the commit body ("easier to read, shorter") is rather terse and
> subjective.  It would be nicer to go into details (change the definition
> of default_alias_machine) or give a sample of what changes (use grep
> instead of awk).

I agree with you. Adding more details as below,
Replacing sed with awk, then it's easier to read.
Replacing "[ ! -z "$default_alias_machine" ]" with "[[ $default_alias_machine ]]",
then it's slightly shorter.

>
> [meta-comment]
>
> When sending a series, please include a 0/4 cover letter.  You may want
> to do:
> git config format.coverLetter auto
> to make it automatic when using git format-patch/send-email.

My understanding is that cover letter is needed if the patch set is a little bit complicated.
Cover letter is not needed if patch set just has minor change and comment is already in the
git message for every patch.
If my understanding above is wrong, please correct me. I just hope to be more clear about process :-)

>> Suggested-By: Sascha Silbe <silbe@linux.vnet.ibm.com>
>> Reviewed-by: Sascha Silbe <silbe@linux.vnet.ibm.com>
>> Signed-off-by: Bo Tu <tubo@linux.vnet.ibm.com>
>> ---
>>   tests/qemu-iotests/common.config | 7 +++----
>>   1 file changed, 3 insertions(+), 4 deletions(-)
>>
>> diff --git a/tests/qemu-iotests/common.config b/tests/qemu-iotests/common.config
>> index 596bb2b..0a165e8 100644
>> --- a/tests/qemu-iotests/common.config
>> +++ b/tests/qemu-iotests/common.config
>> @@ -129,10 +129,9 @@ export QEMU_IO=_qemu_io_wrapper
>>   export QEMU_NBD=_qemu_nbd_wrapper
>>   
>>   default_machine=$($QEMU -machine \? | awk '/(default)/{print $1}')
>> -default_alias_machine=$($QEMU -machine \? |\
>> -    awk -v var_default_machine="$default_machine"\)\
>> -    '{if ($(NF-2)=="(alias"&&$(NF-1)=="of"&&$(NF)==var_default_machine){print $1}}')
>> -if [ ! -z "$default_alias_machine" ]; then
>> +default_alias_machine=$($QEMU -machine \? \
> As long as we are touching this, we ought to switch to using '-machine
> help' rather than the deprecated '-machine \?'.

thanks to point this.

>
>> +    | grep -F "(alias of ${default_machine})" |cut -d ' ' -f 1 |head -n 1)
> Why are you moving the | across lines?

thanks to point this

>
> If we are rewriting to avoid awk, why not do it with a single sed
> process, rather than a grep|cut|head pipeline?  For that matter, why not
> rewrite default_machine to also avoid awk?

The goal is not to avoid awk. The line of default_machine is easy to read, but the
line of default_alias_machine as below is not easy to read, that's why Sascha
suggest me to change it for the line of default_alias_machine.

/-default_alias_machine=$($QEMU -machine \? |\ -    awk -v 
var_default_machine="$default_machine"\)\ -    '{if 
($(NF-2)=="(alias"&&$(NF-1)=="of"&&$(NF)==var_default_machine){print $1}}')/

>
> default_machine=$($QEMU -machine help | sed -n '/(default)/ s/ .*//p')
> default_alias_machine=$($QEMU -machine help | \
>    sed -n "/(alias of $default_machine)"' { s/ .*//p; q; }')
>
> (which happens to work even if $default_machine contains '.', but might
> get a bit dicey if the machine names could ever contain ?, [, *, or
> other regex metacharacters)

I like the single sed process. However, I got error message as below after running it,
/sed: -e expression #1, char 38: unknown command: `.' /I guess you missed a '/' which is marked as red as below, So I change it as below,
/default_machine=$($QEMU -machine help | sed -n '/(default)/ s/ .*//p') 
default_alias_machine=$($QEMU -machine help | \ sed -n "/(alias of 
$default_machine)"/' { s/ .*//p; q; }') /

>
>> +if [ -n "$default_alias_machine" ]; then
> Could shorten this to:
>
> if [[ $default_alias_machine ]]; then

thanks to point this.

>
> since we are already using bash.
>