linux-kernel - [PATCH] f2fs: compress: Allow modular (de)compression algorithms

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Date:   Mon, 22 Feb 2021 13:59:16 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH] f2fs: compress: Allow modular (de)compression algorithms

If F2FS_FS is modular, enabling the compressions options
F2FS_FS_{LZ4,LZ4HZ,LZO,LZORLE,ZSTD} will make the (de)compression
algorithms {LZ4,LZ4HC,LZO,ZSTD}_{,DE}COMPRESS builtin instead of
modular, as the former depend on an intermediate boolean
F2FS_FS_COMPRESSION, which in-turn depends on tristate F2FS_FS.

Indeed, if a boolean symbol A depends directly on a tristate symbol B
and selects another tristate symbol C:

    tristate B

    tristate C

    bool A
      depends on B
      select C

and B is modular, then C will also be modular.

However, if there is an intermediate boolean D in the dependency chain
between A and B:

    tristate B

    tristate C

    bool D
      depends on B

    bool A
      depends on D
      select C

then the modular state won't propagate from B to C, and C will be
builtin instead of modular.

Fix this by making the various compression options depend directly on
F2FS_FS using a big if/endif block.  Drop the now superfluous
dependencies on F2FS_FS from individual symbols.

Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
---
Perhaps the propagation logic in Kconfig should be fixed instead?
Else people may reintroduce this issue when removing seemingly-unneeded
dependencies.
---
 fs/f2fs/Kconfig | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/Kconfig b/fs/f2fs/Kconfig
index 62e638a49bbf089a..20a82ecb72b42f84 100644
--- a/fs/f2fs/Kconfig
+++ b/fs/f2fs/Kconfig
@@ -20,9 +20,10 @@ config F2FS_FS
 
 	  If unsure, say N.
 
+if F2FS_FS
+
 config F2FS_STAT_FS
 	bool "F2FS Status Information"
-	depends on F2FS_FS
 	default y
 	help
 	  /sys/kernel/debug/f2fs/ contains information about all the partitions
@@ -35,7 +36,6 @@ config F2FS_STAT_FS
 
 config F2FS_FS_XATTR
 	bool "F2FS extended attributes"
-	depends on F2FS_FS
 	default y
 	help
 	  Extended attributes are name:value pairs associated with inodes by
@@ -70,7 +70,6 @@ config F2FS_FS_SECURITY
 
 config F2FS_CHECK_FS
 	bool "F2FS consistency checking feature"
-	depends on F2FS_FS
 	help
 	  Enables BUG_ONs which check the filesystem consistency in runtime.
 
@@ -78,7 +77,6 @@ config F2FS_CHECK_FS
 
 config F2FS_FAULT_INJECTION
 	bool "F2FS fault injection facility"
-	depends on F2FS_FS
 	help
 	  Test F2FS to inject faults such as ENOMEM, ENOSPC, and so on.
 
@@ -86,7 +84,6 @@ config F2FS_FAULT_INJECTION
 
 config F2FS_FS_COMPRESSION
 	bool "F2FS compression feature"
-	depends on F2FS_FS
 	help
 	  Enable filesystem-level compression on f2fs regular files,
 	  multiple back-end compression algorithms are supported.
@@ -137,3 +134,5 @@ config F2FS_FS_LZORLE
 	default y
 	help
 	  Support LZO-RLE compress algorithm, if unsure, say Y.
+
+endif
-- 
2.25.1