Squashfs: Make ZLIB compression support optional

Squashfs now supports XZ and LZO compression in addition to ZLIB.
As such it no longer makes sense to always include ZLIB support.
In particular embedded systems may only use LZO or XZ compression, and
the ability to exclude ZLIB support will reduce kernel size.

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>

fs/squashfs/Kconfig

@@ -1,7 +1,6 @@
 config SQUASHFS
 	tristate "SquashFS 4.0 - Squashed file system support"
 	depends on BLOCK
-	select ZLIB_INFLATE
 	help
 	  Saying Y here includes support for SquashFS 4.0 (a Compressed
 	  Read-Only File System).  Squashfs is a highly compressed read-only
@@ -36,6 +35,19 @@ config SQUASHFS_XATTR
 
 	  If unsure, say N.
 
+config SQUASHFS_ZLIB
+	bool "Include support for ZLIB compressed file systems"
+	depends on SQUASHFS
+	select ZLIB_INFLATE
+	default y
+	help
+	  ZLIB compression is the standard compression used by Squashfs
+	  file systems.  It offers a good trade-off between compression
+	  achieved and the amount of CPU time and memory necessary to
+	  compress and decompress.
+
+	  If unsure, say Y.
+
 config SQUASHFS_LZO
 	bool "Include support for LZO compressed file systems"
 	depends on SQUASHFS

fs/squashfs/Makefile

@@ -4,7 +4,8 @@
 
 obj-$(CONFIG_SQUASHFS) += squashfs.o
 squashfs-y += block.o cache.o dir.o export.o file.o fragment.o id.o inode.o
-squashfs-y += namei.o super.o symlink.o zlib_wrapper.o decompressor.o
+squashfs-y += namei.o super.o symlink.o decompressor.o
 squashfs-$(CONFIG_SQUASHFS_XATTR) += xattr.o xattr_id.o
 squashfs-$(CONFIG_SQUASHFS_LZO) += lzo_wrapper.o
 squashfs-$(CONFIG_SQUASHFS_XZ) += xz_wrapper.o
+squashfs-$(CONFIG_SQUASHFS_ZLIB) += zlib_wrapper.o

fs/squashfs/decompressor.c

@@ -52,6 +52,12 @@ static const struct squashfs_decompressor squashfs_xz_comp_ops = {
 };
 #endif
 
+#ifndef CONFIG_SQUASHFS_ZLIB
+static const struct squashfs_decompressor squashfs_zlib_comp_ops = {
+	NULL, NULL, NULL, ZLIB_COMPRESSION, "zlib", 0
+};
+#endif
+
 static const struct squashfs_decompressor squashfs_unknown_comp_ops = {
 	NULL, NULL, NULL, 0, "unknown", 0
 };

fs/squashfs/decompressor.h

@@ -56,4 +56,8 @@ extern const struct squashfs_decompressor squashfs_xz_comp_ops;
 extern const struct squashfs_decompressor squashfs_lzo_comp_ops;
 #endif
 
+#ifdef CONFIG_SQUASHFS_ZLIB
+extern const struct squashfs_decompressor squashfs_zlib_comp_ops;
+#endif
+
 #endif

fs/squashfs/squashfs.h

@@ -97,6 +97,3 @@ extern const struct inode_operations squashfs_symlink_inode_ops;
 
 /* xattr.c */
 extern const struct xattr_handler *squashfs_xattr_handlers[];
-
-/* zlib_wrapper.c */
-extern const struct squashfs_decompressor squashfs_zlib_comp_ops;