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[20090927]
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Looking at the new kernel modules in NetBSD-current
In contrast to the current and previous NetBSD releases,
NetBSD-current and the next major release (6.0) uses a new
system for kernel modules. Unlike the "old" loadable kernel
modules (LKMs), the new module framework supports dependencies
between modules, and loading of kernel modules on demand.
Today, I've found time to install NetBSD-current/i386, and configure
things that I use here - /kern, /proc, and some NFS, in addition to
a local disk. Now, looking at the list of loaded kernel modules reveals:
% modstat
NAME CLASS SOURCE REFS SIZE REQUIRES
compat misc builtin 0 - -
coredump misc filesys 1 3067 -
exec_elf32 misc filesys 0 7225 coredump
exec_script misc filesys 0 1187 -
ffs vfs boot 0 166292 -
kernfs vfs filesys 0 11131 -
nfs vfs filesys 0 145345 -
procfs vfs filesys 0 28068 -
ptyfs vfs filesys 0 8975 -
Interesting points here are that nfs, kernfs and procfs are just listed
in /etc/fstab, and the related filesystem modules
are loaded automatically, without a need to worry if they are
needed or not. In fact I just assumed NFS is in the GENERIC kernel.
Seems it's loaded as module! ;)
Another interesting module is "coredump", which is loaded by the
module to execure 32bit ELF programs, exec_elf32. This is an example
of module dependencies, and again no manual intervention was needed.
So what modules are there? First, let's remember that kernel modules
are object code that implements facilities for the running kernel,
and which interfaces closely with the running kernel. As such, they
need to match the kernel version, ideally. When one of the kernel's
API or ABI interfaces changes, it's best to rebuild all modules.
For NetBSD, the kernel's version is bumped e.g. from 5.99.15 to 5.99.16
for such an interface change, which helps tracking those changes.
Back to the question of what modules are there. Now that we know
kernel modules are closely tied to the version of the kernel
(which still is in the file /netbsd, btw), associated modules
-- for the example of NetBSD/i386 5.99.15 -- can be found in
/stand/i386/5.99.15/modules:
% cd /stand/i386/5.99.15/modules
% ls -F
accf_dataready/ drm/ lfs/ ptyfs/
accf_httpready/ efs/ mfs/ puffs/
adosfs/ exec_aout/ miniroot/ putter/
aio/ exec_elf32/ mqueue/ radeondrm/
azalia/ exec_script/ msdos/ smbfs/
cd9660/ ext2fs/ nfs/ sysvbfs/
coda/ fdesc/ nfsserver/ tmpfs/
coda5/ ffs/ nilfs/ tprof/
compat/ filecore/ ntfs/ tprof_pmi/
compat_freebsd/ fss/ null/ udf/
compat_ibcs2/ hfs/ overlay/ umap/
compat_linux/ i915drm/ portal/ union/
compat_ossaudio/ kernfs/ ppp_bsdcomp/ vnd/
compat_svr4/ ksem/ ppp_deflate/
coredump/ layerfs/ procfs/
% ls */*.kmod
accf_dataready/accf_dataready.kmod layerfs/layerfs.kmod
accf_httpready/accf_httpready.kmod lfs/lfs.kmod
adosfs/adosfs.kmod mfs/mfs.kmod
aio/aio.kmod miniroot/miniroot.kmod
azalia/azalia.kmod mqueue/mqueue.kmod
cd9660/cd9660.kmod msdos/msdos.kmod
coda/coda.kmod nfs/nfs.kmod
coda5/coda5.kmod nfsserver/nfsserver.kmod
compat/compat.kmod nilfs/nilfs.kmod
compat_freebsd/compat_freebsd.kmod ntfs/ntfs.kmod
compat_ibcs2/compat_ibcs2.kmod null/null.kmod
compat_linux/compat_linux.kmod overlay/overlay.kmod
compat_ossaudio/compat_ossaudio.kmod portal/portal.kmod
compat_svr4/compat_svr4.kmod ppp_bsdcomp/ppp_bsdcomp.kmod
coredump/coredump.kmod ppp_deflate/ppp_deflate.kmod
drm/drm.kmod procfs/procfs.kmod
efs/efs.kmod ptyfs/ptyfs.kmod
exec_aout/exec_aout.kmod puffs/puffs.kmod
exec_elf32/exec_elf32.kmod putter/putter.kmod
exec_script/exec_script.kmod radeondrm/radeondrm.kmod
ext2fs/ext2fs.kmod smbfs/smbfs.kmod
fdesc/fdesc.kmod sysvbfs/sysvbfs.kmod
ffs/ffs.kmod tmpfs/tmpfs.kmod
filecore/filecore.kmod tprof/tprof.kmod
fss/fss.kmod tprof_pmi/tprof_pmi.kmod
hfs/hfs.kmod udf/udf.kmod
i915drm/i915drm.kmod umap/umap.kmod
kernfs/kernfs.kmod union/union.kmod
ksem/ksem.kmod vnd/vnd.kmod
% find . -type f -print | wc -l
58
There are directories with major kernel subsystems in the named
directory, each one containing various files with the ".kmod" extension,
for kernel modules. Subsystems include kernel accept filters,
various file systems, compatibility modules, execution modules
for various binary formats, and many others. Currently there are
58 kernel modules, and I guess we can expect more in the future.
P.S.: I've seen one confusion WRT systems that use kernel modules to
whatever extent, as they shrink the size of the actual kernel
binary: Even with kernel modules, an operating system
is still a monolithic kernel: The modules are tied in closely
into the system once loaded, ending in a monolithic system.
In contrast, a "microkernel" is something
very different,
and it doesn't have anything to do with kernel modules. :-)
[Tags: kernel, lkm, modules]
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