[libvirt] [PATCH] virt-wireshark.m4: Defer $(prefix) substitution

[Michal Privoznik]

On 20.10.2016 22:33, Andrea Bolognani wrote:
> On Thu, 2016-10-20 at 15:54 +0800, Michal Privoznik wrote:
>> The problem with evaluating $(prefix) in configure phase is that
>> autoconf does a lot of magic with this variable. Firstly, if the
>> --prefix argument is not set for the configure script, the
>> variable will have value "NONE". Wait, wat? Secondly, even
>> autoconf scripts then have special cases for when variable is
>> "NONE". It's even worse - whenever they need to construct new
>> path based on prefix, they save its current value, substitute it
>> with proper value (like /usr/local/), do what they need and then
>> restore the original value. Le sigh.
>> This mad behaviour is, however, suppressed if there's --prefix on
>> the configure command line.
>> Now, the problem is that we tried to construct path for wireshark
>> plugin in the m4 file. Based on the knowledge described above, we
>> shouldn't do it and just construct the full path in Makefile
>> later where prefix has proper value.
> 
> I don't think we need to go into so much detail, we can just
> point to the autoconf manual[1] which tells us *not* to use
> these variables outside of Makefiles so that users still have
> a chance to override $(prefix) at 'make' or 'make install'
> time.
> 
>> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>> ---
>>   m4/virt-wireshark.m4 | 2 +-
>>   tools/Makefile.am    | 2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>  
>> diff --git a/m4/virt-wireshark.m4 b/m4/virt-wireshark.m4
>> index f383e2b..e1e4a59 100644
>> --- a/m4/virt-wireshark.m4
>> +++ b/m4/virt-wireshark.m4
>> @@ -38,7 +38,7 @@ AC_DEFUN([LIBVIRT_CHECK_WIRESHARK],[
>>           if test "x$ws_prefix" = "x" ; then
>>             ws_prefix="/usr";
>>           fi
>> -        plugindir="${prefix}${plugindir#$ws_prefix}"
>> +        plugindir="${plugindir#$ws_prefix}"
> 
> This got me wondering: is what we're doing even correct?
> 
> If the plugindir for wireshark is eg.
> /usr/lib64/wireshark/plugins, should we still install under
> an arbitrary $(prefix)? Will wireshark pick up the plugin
> then?

Well, depends how you installed wireshark. If you provided the same
prefix during its installation, the plugin is loaded. If you didn't,
then it isn't loaded. But that's what you want, isn't it?

> 
>>         fi
>>       elif test "x$with_ws_plugindir" = "xno" || test "x$with_ws_plugindir" = "xyes"; then
>>         AC_MSG_ERROR([ws-plugindir must be used only with valid path])
>> diff --git a/tools/Makefile.am b/tools/Makefile.am
>> index e7e42c3..08e1680 100644
>> --- a/tools/Makefile.am
>> +++ b/tools/Makefile.am
>> @@ -398,7 +398,7 @@ EXTRA_DIST += \
>>   
>>   if WITH_WIRESHARK_DISSECTOR
>>   
>> -ws_plugindir = $(plugindir)
>> +ws_plugindir = $(prefix)$(plugindir)
>>   ws_plugin_LTLIBRARIES = wireshark/src/libvirt.la
>>   wireshark_src_libvirt_la_CPPFLAGS = \
>>   	-I wireshark/src $(WIRESHARK_DISSECTOR_CFLAGS)
> 
> ACK
> 

Pushed thanks.

Michal