[03/37] libxfs: port IS_ENABLED from the kernel

Commit Message

Darrick J. Wong Oct. 21, 2024, 9:59 p.m. UTC

From: Darrick J. Wong <[e-mail]>

Port the IS_ENABLED macro from the kernel so that it can be used in
libxfs.  This requires a bit of hygiene on our part -- any CONFIG_XFS_*
define in userspace that have counterparts in the kernel must be defined
to 1 (and not simply define'd) so that the macro works, because the
kernel translates CONFIG_FOO=y in .config to #define CONFIG_FOO 1.

Signed-off-by: Darrick J. Wong <[e-mail]>
---
 include/libxfs.h        |    6 +++-
 include/platform_defs.h |   63 +++++++++++++++++++++++++++++++++++++++++++++++
 libxfs/libxfs_priv.h    |    5 ++--
 3 files changed, 70 insertions(+), 4 deletions(-)

Comments

Christoph Hellwig Oct. 22, 2024, 5:58 a.m. UTC | #1

Looks good:

Reviewed-by: Christoph Hellwig <[e-mail]>

Patch

diff --git a/include/libxfs.h b/include/libxfs.h
index 17cf619f0544aa..fe8e6584f1caca 100644
--- a/include/libxfs.h
+++ b/include/libxfs.h
@@ -7,10 +7,12 @@ 
 #ifndef __LIBXFS_H__
 #define __LIBXFS_H__
 
+/* CONFIG_XFS_* must be defined to 1 to work with IS_ENABLED() */
+
 /* For userspace XFS_RT is always defined */
-#define CONFIG_XFS_RT
+#define CONFIG_XFS_RT 1
 /* Ditto in-memory btrees */
-#define CONFIG_XFS_BTREE_IN_MEM
+#define CONFIG_XFS_BTREE_IN_MEM 1
 
 #include "libxfs_api_defs.h"
 #include "platform_defs.h"
diff --git a/include/platform_defs.h b/include/platform_defs.h
index c01d4c42674669..a3644dea41cdef 100644
--- a/include/platform_defs.h
+++ b/include/platform_defs.h
@@ -165,4 +165,67 @@  static inline size_t __ab_c_size(size_t a, size_t b, size_t c)
 # define barrier() __memory_barrier()
 #endif
 
+/* stuff from include/linux/kconfig.h */
+#define __ARG_PLACEHOLDER_1 0,
+#define __take_second_arg(__ignored, val, ...) val
+
+/*
+ * The use of "&&" / "||" is limited in certain expressions.
+ * The following enable to calculate "and" / "or" with macro expansion only.
+ */
+#define __and(x, y)			___and(x, y)
+#define ___and(x, y)			____and(__ARG_PLACEHOLDER_##x, y)
+#define ____and(arg1_or_junk, y)	__take_second_arg(arg1_or_junk y, 0)
+
+#define __or(x, y)			___or(x, y)
+#define ___or(x, y)			____or(__ARG_PLACEHOLDER_##x, y)
+#define ____or(arg1_or_junk, y)		__take_second_arg(arg1_or_junk 1, y)
+
+/*
+ * Helper macros to use CONFIG_ options in C/CPP expressions. Note that
+ * these only work with boolean and tristate options.
+ */
+
+/*
+ * Getting something that works in C and CPP for an arg that may or may
+ * not be defined is tricky.  Here, if we have "#define CONFIG_BOOGER 1"
+ * we match on the placeholder define, insert the "0," for arg1 and generate
+ * the triplet (0, 1, 0).  Then the last step cherry picks the 2nd arg (a one).
+ * When CONFIG_BOOGER is not defined, we generate a (... 1, 0) pair, and when
+ * the last step cherry picks the 2nd arg, we get a zero.
+ */
+#define __is_defined(x)			___is_defined(x)
+#define ___is_defined(val)		____is_defined(__ARG_PLACEHOLDER_##val)
+#define ____is_defined(arg1_or_junk)	__take_second_arg(arg1_or_junk 1, 0)
+
+/*
+ * IS_BUILTIN(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y', 0
+ * otherwise. For boolean options, this is equivalent to
+ * IS_ENABLED(CONFIG_FOO).
+ */
+#define IS_BUILTIN(option) __is_defined(option)
+
+/*
+ * IS_MODULE(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'm', 0
+ * otherwise.  CONFIG_FOO=m results in "#define CONFIG_FOO_MODULE 1" in
+ * autoconf.h.
+ */
+#define IS_MODULE(option) __is_defined(option##_MODULE)
+
+/*
+ * IS_REACHABLE(CONFIG_FOO) evaluates to 1 if the currently compiled
+ * code can call a function defined in code compiled based on CONFIG_FOO.
+ * This is similar to IS_ENABLED(), but returns false when invoked from
+ * built-in code when CONFIG_FOO is set to 'm'.
+ */
+#define IS_REACHABLE(option) __or(IS_BUILTIN(option), \
+				__and(IS_MODULE(option), __is_defined(MODULE)))
+
+/*
+ * IS_ENABLED(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y' or 'm',
+ * 0 otherwise.  Note that CONFIG_FOO=y results in "#define CONFIG_FOO 1" in
+ * autoconf.h, while CONFIG_FOO=m results in "#define CONFIG_FOO_MODULE 1".
+ */
+#define IS_ENABLED(option) __or(IS_BUILTIN(option), IS_MODULE(option))
+
 #endif	/* __XFS_PLATFORM_DEFS_H__ */
diff --git a/libxfs/libxfs_priv.h b/libxfs/libxfs_priv.h
index b720cc5fac94ff..fa025aeb09712b 100644
--- a/libxfs/libxfs_priv.h
+++ b/libxfs/libxfs_priv.h
@@ -37,8 +37,9 @@ 
 #ifndef __LIBXFS_INTERNAL_XFS_H__
 #define __LIBXFS_INTERNAL_XFS_H__
 
-#define CONFIG_XFS_RT
-#define CONFIG_XFS_BTREE_IN_MEM
+/* CONFIG_XFS_* must be defined to 1 to work with IS_ENABLED() */
+#define CONFIG_XFS_RT 1
+#define CONFIG_XFS_BTREE_IN_MEM 1
 
 #include "libxfs_api_defs.h"
 #include "platform_defs.h"