bzip2/lzma: use a table to search for initramfs compression formats

Impact: Code simplification

Instead of open-coding testing for initramfs compression formats, use
a table.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

init/do_mounts_rd.c

@@ -49,6 +49,24 @@ static int __init crd_load(int in_fd, int out_fd, decompress_fn deco);
  *	cramfs
  *	gzip
  */
+static const struct compress_format {
+	unsigned char magic[2];
+	const char *name;
+	decompress_fn decompressor;
+} compressed_formats[] = {
+#ifdef CONFIG_RD_GZIP
+	{ {037, 0213}, "gzip", gunzip },
+	{ {037, 0236}, "gzip", gunzip },
+#endif
+#ifdef CONFIG_RD_BZIP2
+	{ {0x42, 0x5a}, "bzip2", bunzip2 },
+#endif
+#ifdef CONFIG_RD_LZMA
+	{ {0x5d, 0x00}, "lzma", unlzma },
+#endif
+	{ {0, 0}, NULL, NULL }
+};
+
 static int __init
 identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
 {
@@ -59,6 +77,7 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
 	struct cramfs_super *cramfsb;
 	int nblocks = -1;
 	unsigned char *buf;
+	const struct compress_format *cf;
 
 	buf = kmalloc(size, GFP_KERNEL);
 	if (!buf)
@@ -71,52 +90,21 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
 	memset(buf, 0xe5, size);
 
 	/*
-	 * Read block 0 to test for gzipped kernel
+	 * Read block 0 to test for compressed kernel
 	 */
 	sys_lseek(fd, start_block * BLOCK_SIZE, 0);
 	sys_read(fd, buf, size);
 
-#ifdef CONFIG_RD_GZIP
-	/*
-	 * If it matches the gzip magic numbers, return 0
-	 */
-	if (buf[0] == 037 && ((buf[1] == 0213) || (buf[1] == 0236))) {
+	for (cf = compressed_formats; cf->decompressor; cf++) {
+		if (buf[0] == cf->magic[0] && buf[1] == cf->magic[1]) {
 			printk(KERN_NOTICE
-		       "RAMDISK: Compressed image found at block %d\n",
-		       start_block);
-		*decompressor = gunzip;
+			       "RAMDISK: %s image found at block %d\n",
+			       cf->name, start_block);
+			*decompressor = cf->decompressor;
 			nblocks = 0;
 			goto done;
 		}
-#endif
-
-#ifdef CONFIG_RD_BZIP2
-	/*
-	 * If it matches the bzip2 magic numbers, return -1
-	 */
-	if (buf[0] == 0x42 && (buf[1] == 0x5a)) {
-		printk(KERN_NOTICE
-		       "RAMDISK: Bzipped image found at block %d\n",
-		       start_block);
-		*decompressor = bunzip2;
-		nblocks = 0;
-		goto done;
 	}
-#endif
-
-#ifdef CONFIG_RD_LZMA
-	/*
-	 * If it matches the lzma magic numbers, return -1
-	 */
-	if (buf[0] == 0x5d && (buf[1] == 0x00)) {
-		printk(KERN_NOTICE
-		       "RAMDISK: Lzma image found at block %d\n",
-		       start_block);
-		*decompressor = unlzma;
-		nblocks = 0;
-		goto done;
-	}
-#endif
 
 	/* romfs is at block zero too */
 	if (romfsb->word0 == ROMSB_WORD0 &&