New kernel configuration system

Wojciech A. Koszek
wkoszek@FreeBSD.org
http://FreeBSD.czest.pl/~wkoszek/

Current kernel configuration system has its roots in old BSD days. It's similar to sysinstall – it does the job, but the FreeBSD world would be a bit better with having different/better config(8). The goal of the page is to list config(8) limitations and problems hitting us in FreeBSD-9 times. This may be a root of “config(8) suck less” project.

This page contains some ideas about config(8) in random
order. Some are outdated, but later ones are relatively
new. Keep that in mind while studying this page.

Current implementation of kernel configuration tool has a lot of problems and shortcomings that make a life of typical FreeBSD user much hard. Below I try to address them:

• build all .c files just once, and use object files to create the kernel and modules
  • right now we actually compile kernel twice–for the kernel and modules separately
• support dependencies – right now when some option is missing, you'll get link time error
  • try to keep nice structure of conf/files, since it's relatively easy to insert file there
  • this is stricly related with entry above
  • do NOT block advanced users from providing their own .o (custom) files if they want it (Peter)
• support out-of-tree module build
  • or at least be smart enough to let us to remove (or limit) src/sys/modules; stay away from empty opt_*.h recreation.
• support “kernel will accept this KLD for sure and won't panic”:
  • compile the kernel against particular kernel – if the kernel has INVARIANTS, KLD should be compiled with INVARIANTS as well.

• DSL implemented:
  • nooption nosomething
  • enable disable
  • …and other don't work well.

• be able to configure cross-arch kernels

• include whole src/sys stuff (imp@)
  • include only .c files, from which kernel has been built (des@)

• INCLUDE_CONFIG_FILE should include comments in the generated output

Proposed syntax for the new kernel configurator a.k.a config2:

component kernel {
         files {
                kern_main.c,
                kern_exec.c,
                [...]
         };
};

component md {
         files {
                md.c
         };
};

component mii {
          files {
                 mii.c
          };
};

component acphy {
          files {
                   dev/mii/acphy.c
          };
          depends {
                   mii
          };  
};

component amphy {
          files {
                 dev/mii/amphy.c
          };
          depends {
                   mii
          }; 
};

component miibus {
          embed {
                   mii, amphy, acphy
          };
};

component em {
          compile_with "${NORMAL_C} -I$S/dev/e1000";    // compile_with can take block or a string
          files {
                  dev/e1000/if_em.c
                  dev/e1000/if_lem.c
                  dev/e1000/if_igb.c
                  dev/e1000/e1000_80003es2lan.c
                  dev/e1000/e1000_82540.c

                  [...]
           };
};

component ipwibssfw {
           compile_with {                            // compile_with as a block + possibility of line breaking
                   ${AWK} -f $S/tools/fw_stub.awk ipw_ibss.fw:ipw_ibss:130
                       -lintel_ipw -mipw_ibss -c${.TARGET}
           };

           clean "ipwibssfw.c";                      // I think we could either accept {} block or a string for single statements
                  
           no_implicit_rule;
           before_depend;
           local (XXWKOSZEK: need to figure out what that is)
        
};

Keyword component would define what functionality is provided.

Keyword files would be used to start a block with c files enlisted.

Keyword embed just picks the content of previous blocks and merges them in a current block.

Keyword compile_with sets the generation command

Keywords “no_implicit_rule”, “before_depend”, “local” stay as they were.

static kernel;                 // this could be implicit or not
static md;                     

makeoptions "DEBUG=-g"

options         SCHED_ULE               # Some options would stay
options         PREEMPTION              #
options         INET                    #
options         INET6                   #

options         NFSCL                   # but some COULD probably be just
options         NFSD                    # included as "static nfscl"
options         NFSLOCKD                # Why would NFS be included as an "options?"

With “components” and dependencies, src/sys/modules could go away, so modules would be built 'for free'. And kernel configuration would only enlist things necessary for components that we want to link staticly.

In my view, we should use the same parsing for src/sys/conf/files' and src/sys/<arch>/conf/KERNCONF, so that

cat src/sys/conf/files src/sys/amd64/conf/KERNCONF > kconf
config2 -f kconf

is possible. The reason is that for development, I'd like to have kern_something.c included from my KERNCONF and the whole case with parsing would just be simplified.

The idea which Peter prototyped already in the past was to use config(8) to dump configuration data in the form of easily parseable tables, which would later get consumed by scripts.

It would be scripts that generate Makefiles and other metadata files necessary by a boot process.

Study once again conversations from 2007-05-16-