bzip2/lzma: comprehensible error messages for missing decompressor

Instead of failing to identify a compressed image with a decompressor
that we don't have compiled in, identify it and fail with a
comprehensible panic message.

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

3 files changed, 25 insertions, 8 deletions

diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
index a015e267fd17..91d0cfca5071 100644
--- a/init/do_mounts_rd.c
+++ b/init/do_mounts_rd.c
@@ -79,9 +79,12 @@ identify_ramdisk_image(int fd, int start_block, decompress_fn *decompressor)
         sys_read(fd, buf, size);
 
         *decompressor = decompress_method(buf, size, &compress_name);
-        if (*decompressor) {
+        if (compress_name) {
                 printk(KERN_NOTICE "RAMDISK: %s image found at block %d\n",
                        compress_name, start_block);
+                if (!*decompressor)
+                        printk(KERN_CRIT "RAMDISK: %s decompressor not configured!\n",
+                               compress_name);
                 nblocks = 0;
                 goto done;
         }
diff --git a/init/initramfs.c b/init/initramfs.c
index 76f4a0125338..9a7290ec8187 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -421,6 +421,8 @@ static char * __init unpack_to_rootfs(char *buf, unsigned len, int check_only)
 {
         int written;
         decompress_fn decompress;
+        const char *compress_name;
+        static __initdata char msg_buf[64];
 
         dry_run = check_only;
         header_buf = kmalloc(110, GFP_KERNEL);
@@ -449,10 +451,18 @@ static char * __init unpack_to_rootfs(char *buf, unsigned len, int check_only)
                         continue;
                 }
                 this_header = 0;
-                decompress = decompress_method(buf, len, NULL);
+                decompress = decompress_method(buf, len, &compress_name);
                 if (decompress)
                         decompress(buf, len, NULL, flush_buffer, NULL,
                                    &my_inptr, error);
+                else if (compress_name) {
+                        if (!message) {
+                                snprintf(msg_buf, sizeof msg_buf,
+                                         "compression method %s not configured",
+                                         compress_name);
+                                message = msg_buf;
+                        }
+                }
                 if (state != Reset)
                         error("junk in compressed archive");
                 this_header = saved_offset + my_inptr;
diff --git a/lib/decompress.c b/lib/decompress.c
index edac55cc7823..961f367320fc 100644
--- a/lib/decompress.c
+++ b/lib/decompress.c
@@ -13,21 +13,25 @@
 #include <linux/types.h>
 #include <linux/string.h>
 
+#ifndef CONFIG_DECOMPRESS_GZIP
+# define gunzip NULL
+#endif
+#ifndef CONFIG_DECOMPRESS_BZIP2
+# define bunzip2 NULL
+#endif
+#ifndef CONFIG_DECOMPRESS_LZMA
+# define unlzma NULL
+#endif
+
 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 }
 };