bzip2/lzma: use a table to search for initramfs compression formats
H. Peter Anvin [Sun, 4 Jan 2009 22:42:52 +0000 (14:42 -0800)]
Impact: Code simplification

Instead of open-coding testing for initramfs compression formats, use
a table.

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

init/do_mounts_rd.c

index dcaeb1f..9c9d7db 100644 (file)
@@ -43,13 +43,31 @@ static int __init crd_load(int in_fd, int out_fd, decompress_fn deco);
  * numbers could not be found.
  *
  * We currently check for the following magic numbers:
- *     minix
- *     ext2
+ *     minix
+ *     ext2
  *     romfs
  *     cramfs
- *     gzip
+ *     gzip
  */
-static int __init 
+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)
 {
        const int size = 512;
@@ -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))) {
-               printk(KERN_NOTICE
-                      "RAMDISK: Compressed image found at block %d\n",
-                      start_block);
-               *decompressor = gunzip;
-               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;
+       for (cf = compressed_formats; cf->decompressor; cf++) {
+               if (buf[0] == cf->magic[0] && buf[1] == cf->magic[1]) {
+                       printk(KERN_NOTICE
+                              "RAMDISK: %s image found at block %d\n",
+                              cf->name, start_block);
+                       *decompressor = cf->decompressor;
+                       nblocks = 0;
+                       goto done;
+               }
        }
-#endif
 
        /* romfs is at block zero too */
        if (romfsb->word0 == ROMSB_WORD0 &&
@@ -165,7 +153,7 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
        printk(KERN_NOTICE
               "RAMDISK: Couldn't find valid RAM disk image starting at %d.\n",
               start_block);
-       
+
 done:
        sys_lseek(fd, start_block * BLOCK_SIZE, 0);
        kfree(buf);
@@ -224,7 +212,7 @@ int __init rd_load_image(char *from)
                       nblocks, rd_blocks);
                goto done;
        }
-               
+
        /*
         * OK, time to copy in the data
         */