Use MODULE variable in module Makefile like zfs.

In zfs, each module Makefile contains a MODULE variable which contains
the name of the module, and the following declarations reference this
variable.

In spl, there is a MODULES variable which is never used. Rename it to
MODULE and use it like in zfs. This improves consistency between the two
build systems.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue zfsonlinux/zfs#851
Don't build packages that haven't been selected.

Currently, when configure --with-config is used, selective compilation
is only effective for the simple "make" case. Package builders (e.g.
make rpm) still build everything (utils and modules). This patch fixes
that.

This patch also drops the duplicate rpm-modules build target.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Prakash Surya <surya1@llnl.gov>
Issue zfsonlinux/zfs#851
Fix undefined reference on spl_mutex_spin_max().

Commit 3160d4f56bf35492e9c400094f8c1ff2066d4459 changed the set of
conditions under which spl_mutex_spin_max would be implemented as a
function by changing an #if in sys/mutex.h. The corresponding
implementation file spl-mutex.c, however, has not been updated to
reflect the change. This results in undefined reference errors on
spl_mutex_spin_max under the following condition:

((!CONFIG_SMP || CONFIG_DEBUG_MUTEXES) && HAVE_MUTEX_OWNER && HAVE_TASK_CURR)

This patch fixes the issue by using the same #if in sys/mutex.h and
spl-mutex.c.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue zfsonlinux/zfs#851
Make configure builtin-aware.

This patch adds a new option to configure: --enable-linux-builtin. When
this option is used, the following happens:

 - Compilation of kernel modules is disabled.

 - A failure to find UTS_RELEASE is followed by a suggestion to run
   "make prepare" on the kernel source tree.

This patch also adds a new test which tries to compile an empty module
as a basic toolchain sanity test. If it fails and the option was
specified, the error is followed by a suggestion to run "make scripts"
on the kernel source tree.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue zfsonlinux/zfs#851
Fake modpost stage for LINUX_COMPILE.

Currently, when building a test case, we're compiling an entire Linux
module from beginning to end. This includes the MODPOST stage, which
generates a "conftest.mod.c" file with some boilerplate module
declaration code.

This poses a problem when configuring for built-in on kernels which have
loadable module support disabled. In this case conftest.mod.c is
referencing disabled code, resulting in a compilation failure, thus
breaking the tests.

This patch fixes the issue by faking the modpost stage when the
--enable-linux-builtin option is provided.  It does so by forcing the
modpost command to be /bin/true, and using an empty conftest.mod.c file.
The test module still compiles fine, although the result isn't loadable,
but we don't really care at this point.

Note it is important to preserve the modpost stage when building out of
tree.  This allows for the posibility of configure checks to leverage
this phase to identify GPL-only symbols.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue zfsonlinux/zfs#851
When checking for symbol exports, try compiling.

This patch adds a new autoconf function: SPL_LINUX_TRY_COMPILE_SYMBOL.
This new function does the following:

 - Call LINUX_TRY_COMPILE with the specified parameters.
 - If unsuccessful, return false.
 - If successful and we're configuring with --enable-linux-builtin,
   return true.
 - Else, call CHECK_SYMBOL_EXPORT with the specified parameters and
   return the result.

All calls to CHECK_SYMBOL_EXPORT are converted to
LINUX_TRY_COMPILE_SYMBOL so that the tests work even when configuring
for builtin on a kernel which doesn't have loadable module support, or
hasn't been built yet.

The only exception are:

 - AC_GET_VMALLOC_INFO, because we don't even have a public header to
include in the test case, but that's okay considering this symbol can
be ignored just fine.

- SPL_AC_DEVICE_CREATE, which is legacy API for 2.6.18 kernels.  Since
kernels this old are no longer supported it should arguably just be
removed entirely from the build system.

Note that we're also checking for the correct prototype with an actual
call, which was not the case with CHECK_SYMBOL_EXPORT. However, for
"complicated" test cases like with multiple symbol versions (e.g.
vfs_fsync), we stick with the original behavior and only check for the
function's existence.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue zfsonlinux/zfs#851
Add script for builtin module building.

This commit introduces a "copy-builtin" script designed to prepare a
kernel source tree for building SPL as a builtin module. The script
makes a full copy of all needed files, thus making the kernel source
tree fully independent of the spl source package.

To achieve that, some compilation flags (-include, -I) have been moved
to module/Makefile. This Makefile is only used when compiling external
modules; when compiling builtin modules, a Kbuild file generated by the
configure-builtin script is used instead. This makes sure Makefiles
inside the kernel source tree does not contain references to the spl
source package.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue zfsonlinux/zfs#851
Determine the hostid on demand.

Currently, the SPL tries to determine the hostid at module load. The
hostid is usually determined by running the userland program "hostid"
during module initialization.

Unfortunately, when the module initializes, it may be way too soon to be
able to run any userland programs. This is especially true when the
module is compiled directly inside the kernel (built-in); in that case,
the SPL would try to run hostid when the kernel is still initializing,
which of course is doomed to fail.

This patch fixes the issue by deferring hostid generation until
something actually needs the hostid (that is, when zone_get_hostid() is
called), thus switching to a "on-initialization" model to a "on-demand"
(lazy loading) model. ZFS only needs the hostid when some pool
operations are requested, and this always happens way after the kernel
has finished initialization, thus solving the problem.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue zfsonlinux/zfs#851
Merge branch 'builtin-clean'

Support in-tree builtin module building.

These commits add support for compiling the SPL module as a built-in
kernel module by copying the module code into the kernel source tree.
Here's the procedure:

  - Create your kernel configuration (`.config` file) as usual. This
    has to be done first so that SPL's configure script is able to
    detect kernel features correctly.
  - Run `make prepare scripts` inside the kernel source tree.
  - Run `./configure --enable-linux-builtin --with-linux=/usr/src/linux-...`
    inside the SPL directory.
  - Run `./copy-builtin /usr/src/linux-...` inside the SPL directory.
  - In the kernel source tree, enable the `CONFIG_SPL` option
    (e.g. using `make menuconfig`).
  - Build the kernel as usual.

SPL module parameters can be set at boot time using the following syntax
on the kernel command line: `spl.parameter_name=parameter_value`.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue zfsonlinux/zfs#851