Subject: Re: linux-next: Tree for Apr 19 (zcache)

From: Seth Jennings <[email-masked]>
Date: Thu, 19 Apr 2012 23:36:26 -0500

On 04/19/2012 05:36 PM, Dan Magenheimer wrote:
>> From: Randy Dunlap [mailto:[email-masked]]
>> Sent: Thursday, April 19, 2012 4:30 PM
>> To: Stephen Rothwell
>> Cc: [email-masked]; LKML; Dan Magenheimer
>> Subject: Re: linux-next: Tree for Apr 19 (zcache)
>>
>> On 04/18/2012 11:46 PM, Stephen Rothwell wrote:
>>
>>> Hi all,
>>>
>>> Changes since 20120418:
>>
>>
>> on x86_64:
>>
>> drivers/built-in.o: In function `zv_free':
>> zcache-main.c:(.text+0x5e1c9): undefined reference to `zs_map_object'
>> zcache-main.c:(.text+0x5e238): undefined reference to `zs_unmap_object'
>> zcache-main.c:(.text+0x5e29a): undefined reference to `zs_free'
>> drivers/built-in.o: In function `zv_create':
>> zcache-main.c:(.text+0x5e6b3): undefined reference to `zs_malloc'
>> zcache-main.c:(.text+0x5e6f0): undefined reference to `zs_map_object'
>> zcache-main.c:(.text+0x5e72c): undefined reference to `zs_unmap_object'
>> drivers/built-in.o: In function `zcache_comp_init':
>> zcache-main.c:(.text+0x5e831): undefined reference to `crypto_has_alg'
>> zcache-main.c:(.text+0x5e8a5): undefined reference to `crypto_has_alg'
>> drivers/built-in.o: In function `zcache_cpu_notifier':
>> zcache-main.c:(.text+0x5e94f): undefined reference to `crypto_alloc_base'
>> zcache-main.c:(.text+0x5e9f2): undefined reference to `crypto_destroy_tfm'
>> drivers/built-in.o: In function `zv_decompress':
>> zcache-main.c:(.text+0x5ee40): undefined reference to `zs_map_object'
>> zcache-main.c:(.text+0x5ef06): undefined reference to `zs_unmap_object'
>> drivers/built-in.o: In function `zcache_pampd_create':
>> zcache-main.c:(.text+0x5f614): undefined reference to `zs_get_total_size_bytes'
>> make[1]: *** [.tmp_vmlinux1] Error 1

The problem is that zsmalloc is being built as a module and zcache is
builtin.  It seems that because CRYPTO=m, kbuild is forcing zsmalloc
to be built, just not forcing it to be builtin.

The zcache Kconfig has:
	bool "Dynamic compression of swap pages and clean pagecache pages"
	depends on (CLEANCACHE || FRONTSWAP) && CRYPTO && X86
	select ZSMALLOC
	select CRYPTO_LZO

Seems to be a nuance of kbuild I didn't know before.  If a
"selected by" (sub)condition is met, if any of the conditionals are
built as modules, then the entry can be built as a module.

For example, if zsmalloc is selected by:
...(CLEANCACHE [=y] || FRONTSWAP [=n]) && CRYPTO [=m] && X86 [=y]
then it can be built as a module or builtin.

If zsmalloc is selected by:
...(CLEANCACHE [=y] || FRONTSWAP [=n]) && CRYPTO [=y] && X86 [=y]
then it must be builtin.

One fix is this:

diff --git a/drivers/staging/zcache/Kconfig b/drivers/staging/zcache/Kconfig
index 3ed2c8f..7048e01 100644
--- a/drivers/staging/zcache/Kconfig
+++ b/drivers/staging/zcache/Kconfig
@@ -2,7 +2,7 @@ config ZCACHE
        bool "Dynamic compression of swap pages and clean pagecache pages"
        # X86 dependency is because zsmalloc uses non-portable pte/tlb
        # functions
-       depends on (CLEANCACHE || FRONTSWAP) && CRYPTO && X86
+       depends on (CLEANCACHE || FRONTSWAP) && CRYPTO=y && X86
        select ZSMALLOC
        select CRYPTO_LZO
        default n

I think this is the best way since ZCACHE is a bool and CRYPTO is the only
one of the dependencies that is a tristate.  This forces both ZSMALLOC and
CRYPTO_LZO to be builtin if ZCACHE is selected.

Any other suggestions?

Thanks,
Seth