[Crash-utility] RFC: crash extension module handling

Lucio's post of his latest Cell/B.E. SPU commands extension module: https://www.redhat.com/archives/crash-utility/2007-September/msg00041.html leads to a larger discussion of how extension modules should best be handled. In Lucio's patch, he modified the top-level Makefile and the extensions subdirectory Makefile to build his extension module, following the directions in the extensions/Makefile file itself, which states: # To add a new extension object: # # - add the new source file to the EXTENSION_SOURCE_FILES list # in the top-level Makefile # - add the object file name to the EXTENSION_OBJECT_FILES list # in the top-level Makefile # - create a compile stanza below, typically using "echo.so" as # a base template. Now, currently in the extensions subdirectory are two extension modules, echo.c and dminfo.c, and there are explicit compile lines for the two of them, which are identical in nature: echo.so: ../defs.h echo.c gcc -nostartfiles -shared -rdynamic -o echo.so echo.c -fPIC \ -D$(TARGET) $(TARGET_CFLAGS) dminfo.so: ../defs.h dminfo.c gcc -nostartfiles -shared -rdynamic -o dminfo.so dminfo.c -fPIC \ -D$(TARGET) $(TARGET_CFLAGS) and in Lucio's patch, he follows the template: +spu.so: ../defs.h spu.c + gcc -nostartfiles -shared -rdynamic -o spu.so spu.c -fPIC \ + -D$(TARGET) $(TARGET_CFLAGS) That's all well and good, but I've decided that I really don't want the crash source package to be a placeholder of this, and numerous other, extension module source files. My feeling is that the crash package should only have to deal with the *mechanism* of handling dynamic extension modules, and not the modules' source code itself. A little history first... The "echo.c" extension module is simply a template from which a new module can be created. The "dminfo.c" extension module is a special-case Red Hat extension module, created as an alternative to the device-mapper guys from having to write their own utility that would do the same kind of kernel-memory grok'ing that crash does. To be honest, I'd prefer it if it were not there in the crash source tree, but there was no acceptable alternative at the time. Furthermore, since that dminfo.c module was added, the crash src.rpm now creates an additional "crash-devel" rpm, which consists of just the defs.h file, which is the only thing needed for building an extension module, and which is installed in /usr/include/crash/defs.h. So, for example, the systemtap folks have their own crash extension module package that they control on their own. They can simply install the crash-devel package -- without having to install the crash source package -- and with their own package Makefile, they compile their stap module, basically doing their own thing "elsewhere". Had that been in place at the time, the dminfo guys could have done the same type of thing. That being said, it is still convenient for many to be able to do the module building from within a crash source tree's extensions subdirectory. Now, given that extension modules should be compile'able in precisely the same manner as echo.c and dminfo.c, what I'd like to do is simply have the "make extensions" command from the top-level Makefile cause the extensions/Makefile to pick up *any* C file in the extensions subdirectory, and compile a module automatically -- without having to modify the top-level Makefile or extensions/Makefile. In other words, just throw your module's C file into the extensions subdirectory, enter "make extensions" from the top-level, and it gets build automatically. No changes required for the top-level Makefile, no changes required for the extensions/Makefile, nor any need to store a myriad of extension modules in the crash source tree. BTW, I'm perfectly willing to add an "extensions" repository accessible from my people page, where contributors can store their latest-and-greatest. Anyway, I've been tinkering with the extensions/Makefile to do such a thing, and have a crude addition that does just that, although it does the compile of all "new" C files every time whether they need it or not -- via the additional "contrib" target: 30c30 < all: link_defs $(OBJECTS) --- 43a44,50 sial.c`; do \ -D$(TARGET) $(TARGET_CFLAGS)"; \ $(TARGET_CFLAGS); \ It prevents the re-compilation of echo.c and dminfo.c, and of Luc Chouinard's upcoming sial.c extension module. (SIAL is an alternative crash extension mechanism -- more on that when it's available...) Anyway, I've tried screwing around with the Makefile to use a generic *.so target, using $@, $(basename ...) and so on, but I'm not a Makefile master, and I cannot quite get it quite right, although I'm sure it can be done. So if anybody out there can do it cleaner than the "contrib" target above, I'd like to take a look. Thanks, Dave