Cleanup and document the implementation of firmware(9) based on

a version that i posted earlier on the -current mailing list,
and subsequent feedback received.

The core of the change is just in sys/firmware.h and kern/subr_firmware.c,
while other files are just adaptation of the clients to the ABI change
(const-ification of some parameters and hiding of internal info,
so this is fully compatible at the binary level).

In detail:
- reduce the amount of information exported to clients in struct firmware,
  and constify the pointer;

- internally, document and simplify the implementation of the various
  functions, and make sure error conditions are dealt with properly.

The diffs are large, but the code is really straightforward now (i hope).

Note also that there is a subtle issue with the implementation of
firmware_register(): currently, as in the previous version, we just
store a reference to the 'imagename' argument, but we should rather
copy it because there is no guarantee that this is a static string.
I realised this while testing this code, but i prefer to fix it in
a later commit -- there is no regression with respect to the past.

Note, too, that the version in RELENG_6 has various bugs including
missing locks around the module release calls, mishandling of modules
loaded by /boot/loader, and so on, so an MFC is absolutely necessary
there.  I was just postponing it until this cleanup to avoid doing
things twice.

MFC after: 1 week

1 files changed, 1 insertions, 1 deletions

diff --git a/sys/tools/fw_stub.awk b/sys/tools/fw_stub.awk
index 3e4463e..40be8ad 100644
--- a/sys/tools/fw_stub.awk
+++ b/sys/tools/fw_stub.awk
@@ -125,7 +125,7 @@ for (file_i = 0; file_i < num_files; file_i++) {
 printc("\nstatic int\n"\
 opt_m "_fw_modevent(module_t mod, int type, void *unused)\
 {\
-	struct firmware *fp, *parent;\
+	const struct firmware *fp, *parent;\
 	int error;\
 	switch (type) {\
 	case MOD_LOAD:");