logfs: clarify MTD dependency

Commit Message

Michal Marek Nov. 27, 2015, 2:14 p.m. UTC

On Fri, Nov 27, 2015 at 02:54:53PM +0100, Arnd Bergmann wrote:
> After a change to the way that composite modules work, we get
> a logfs build error:
> 
> fs/built-in.o: In function `logfs_mount':
> :(.text+0x139d34): undefined reference to `logfs_get_sb_mtd'
> fs/built-in.o: In function `logfs_get_sb_bdev':
> :(.text+0x13aa08): undefined reference to `logfs_get_sb_mtd'
> 
> This patch avoids the error by changing the dependencies of
> logfs in a way that we can no longer configure logfs as built-in
> when the MTD core is a loadable module, while leaving the
> dependency to require at least one of MTD or BLOCK to be
> enabled.

Hi Arnd,

I hit this as well and was about to submit a slightly different fix. Can
you try the logfs portion of the below patch? Proper changelog is to be
done, but the gist of the patch is that IS_REACHABLE(CONFIG_FOO) 
evaluates to 1 if CONFIG_FOO=y or we are building a module and
CONFIG_FOO=m.

Michal

From 63e7ab41e3958e753277728acbe15faf35a5374e Mon Sep 17 00:00:00 2001
From: Michal Marek <[e-mail]>
Date: Fri, 27 Nov 2015 15:08:29 +0100
Subject: [PATCH] kbuild: Use IS_REACHABLE to handle objname-m composite
 objects

Fixes: cf4f21938e13 ("kbuild: Allow to specify composite modules with modname-m")
Signed-off-by: Michal Marek <[e-mail]>
---
 drivers/misc/ibmasm/ibmasm.h   | 2 +-
 drivers/usb/chipidea/otg_fsm.h | 2 +-
 fs/logfs/logfs.h               | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

Comments

Arnd Bergmann Nov. 27, 2015, 2:30 p.m. UTC | #1

On Friday 27 November 2015 15:14:06 Michal Marek wrote:
> 
> Hi Arnd,
> 
> I hit this as well and was about to submit a slightly different fix. Can
> you try the logfs portion of the below patch? Proper changelog is to be
> done, but the gist of the patch is that IS_REACHABLE(CONFIG_FOO) 
> evaluates to 1 if CONFIG_FOO=y or we are building a module and
> CONFIG_FOO=m.
> 

I thought about doing it that way, and I'm sure that also worked.
The possible behaviors are basically:

a) before your original patch, building logfs with CONFIG_MTD=m would
   silently leave out MTD support, which was rather confusing.

b) with my patch, it becomes impossible to have logfs as the built-in
   root file system on a block device while also using CONFIG_MTD=m,
   and that may be slightly annoying

c) your patch restores a), but makes it work in the case where both
   logfs and mtd are loadable modules, which is an improvement but
   may still confuse users.

My preference is still version b) as I sent, but I don't really mind
your version either.

	Arnd

Michal Marek Nov. 27, 2015, 2:50 p.m. UTC | #2

On 2015-11-27 15:30, Arnd Bergmann wrote:
> On Friday 27 November 2015 15:14:06 Michal Marek wrote:
>>
>> Hi Arnd,
>>
>> I hit this as well and was about to submit a slightly different fix. Can
>> you try the logfs portion of the below patch? Proper changelog is to be
>> done, but the gist of the patch is that IS_REACHABLE(CONFIG_FOO) 
>> evaluates to 1 if CONFIG_FOO=y or we are building a module and
>> CONFIG_FOO=m.
>>
> 
> I thought about doing it that way, and I'm sure that also worked.
> The possible behaviors are basically:
> 
> a) before your original patch, building logfs with CONFIG_MTD=m would
>    silently leave out MTD support, which was rather confusing.
> 
> b) with my patch, it becomes impossible to have logfs as the built-in
>    root file system on a block device while also using CONFIG_MTD=m,
>    and that may be slightly annoying
> 
> c) your patch restores a), but makes it work in the case where both
>    logfs and mtd are loadable modules, which is an improvement but
>    may still confuse users.
> 
> My preference is still version b) as I sent, but I don't really mind
> your version either.

I used the IS_REACHABLE macro because it hides the boolean expressions
nicely :). But I also do not insist on a particular solution. Jörn, what
would be your preference?

Thanks,
Michal

Patch

diff --git a/drivers/misc/ibmasm/ibmasm.h b/drivers/misc/ibmasm/ibmasm.h
index 5bd127727d8e..0f4c43a8543e 100644
--- a/drivers/misc/ibmasm/ibmasm.h
+++ b/drivers/misc/ibmasm/ibmasm.h
@@ -211,7 +211,7 @@  void ibmasmfs_unregister(void);
 void ibmasmfs_add_sp(struct service_processor *sp);
 
 /* uart */
-#if IS_ENABLED(CONFIG_SERIAL_8250)
+#if IS_REACHABLE(CONFIG_SERIAL_8250)
 void ibmasm_register_uart(struct service_processor *sp);
 void ibmasm_unregister_uart(struct service_processor *sp);
 #else
diff --git a/drivers/usb/chipidea/otg_fsm.h b/drivers/usb/chipidea/otg_fsm.h
index 262d6ef8df7c..44506e4aa11f 100644
--- a/drivers/usb/chipidea/otg_fsm.h
+++ b/drivers/usb/chipidea/otg_fsm.h
@@ -62,7 +62,7 @@ 
 /* SSEND time before SRP */
 #define TB_SSEND_SRP         (1500)	/* minimum 1.5 sec, section:5.1.2 */
 
-#if IS_ENABLED(CONFIG_USB_OTG_FSM)
+#if IS_REACHABLE(CONFIG_USB_OTG_FSM)
 
 int ci_hdrc_otg_fsm_init(struct ci_hdrc *ci);
 int ci_otg_fsm_work(struct ci_hdrc *ci);
diff --git a/fs/logfs/logfs.h b/fs/logfs/logfs.h
index 23f961a8fb92..2fcd487a4ab2 100644
--- a/fs/logfs/logfs.h
+++ b/fs/logfs/logfs.h
@@ -485,7 +485,7 @@  static inline int logfs_get_sb_bdev(struct logfs_super *s,
 #endif
 
 /* dev_mtd.c */
-#if IS_ENABLED(CONFIG_MTD)
+#if IS_REACHABLE(CONFIG_MTD)
 int logfs_get_sb_mtd(struct logfs_super *s, int mtdnr);
 #else
 static inline int logfs_get_sb_mtd(struct logfs_super *s, int mtdnr)