bzip2/lzma: centralize format detection

Centralize the compression format detection to a common routine in the
lib directory, and use it for both initramfs and initrd.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

2 files changed, 55 insertions, 4 deletions

diff --git a/lib/Makefile b/lib/Makefile
index d9ac5a414fa7..790de7c25d0d 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -11,7 +11,8 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
          rbtree.o radix-tree.o dump_stack.o \
          idr.o int_sqrt.o extable.o prio_tree.o \
          sha1.o irq_regs.o reciprocal_div.o argv_split.o \
-         proportions.o prio_heap.o ratelimit.o show_mem.o is_single_threaded.o
+         proportions.o prio_heap.o ratelimit.o show_mem.o \
+         is_single_threaded.o decompress.o
 
 lib-$(CONFIG_MMU) += ioremap.o
 lib-$(CONFIG_SMP) += cpumask.o
@@ -65,9 +66,9 @@ obj-$(CONFIG_REED_SOLOMON) += reed_solomon/
 obj-$(CONFIG_LZO_COMPRESS) += lzo/
 obj-$(CONFIG_LZO_DECOMPRESS) += lzo/
 
-obj-$(CONFIG_DECOMPRESS_GZIP) += decompress_inflate.o
-obj-$(CONFIG_DECOMPRESS_BZIP2) += decompress_bunzip2.o
-obj-$(CONFIG_DECOMPRESS_LZMA) += decompress_unlzma.o
+lib-$(CONFIG_DECOMPRESS_GZIP) += decompress_inflate.o
+lib-$(CONFIG_DECOMPRESS_BZIP2) += decompress_bunzip2.o
+lib-$(CONFIG_DECOMPRESS_LZMA) += decompress_unlzma.o
 
 obj-$(CONFIG_TEXTSEARCH) += textsearch.o
 obj-$(CONFIG_TEXTSEARCH_KMP) += ts_kmp.o
diff --git a/lib/decompress.c b/lib/decompress.c
new file mode 100644
index 000000000000..edac55cc7823
--- /dev/null
+++ b/lib/decompress.c
@@ -0,0 +1,50 @@
+/*
+ * decompress.c
+ *
+ * Detect the decompression method based on magic number
+ */
+
+#include <linux/decompress/generic.h>
+
+#include <linux/decompress/bunzip2.h>
+#include <linux/decompress/unlzma.h>
+#include <linux/decompress/inflate.h>
+
+#include <linux/types.h>
+#include <linux/string.h>
+
+static const struct compress_format {
+        unsigned char magic[2];
+        const char *name;
+        decompress_fn decompressor;
+} compressed_formats[] = {
+#ifdef CONFIG_DECOMPRESS_GZIP
+        { {037, 0213}, "gzip", gunzip },
+        { {037, 0236}, "gzip", gunzip },
+#endif
+#ifdef CONFIG_DECOMPRESS_BZIP2
+        { {0x42, 0x5a}, "bzip2", bunzip2 },
+#endif
+#ifdef CONFIG_DECOMPRESS_LZMA
+        { {0x5d, 0x00}, "lzma", unlzma },
+#endif
+        { {0, 0}, NULL, NULL }
+};
+
+decompress_fn decompress_method(const unsigned char *inbuf, int len,
+                                const char **name)
+{
+        const struct compress_format *cf;
+
+        if (len < 2)
+                return NULL;    /* Need at least this much... */
+
+        for (cf = compressed_formats; cf->decompressor; cf++) {
+                if (!memcmp(inbuf, cf->magic, 2))
+                        break;
+
+        }
+        if (name)
+                *name = cf->name;
+        return cf->decompressor;
+}