Re: update8 [PATCH 2/5] init: bzip2 or lzma -compressed kernels and initrds

H. Peter Anvin
2009-01-04T23:08:37Z

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Hi Alain,

Looking pretty good now. The only issues that I see so far are:

- Putting the kernel compression selection in init/Kconfig isn't going
to work too well, since it affects all architectures, and not all
architectures even do their own decompression (for quite a few
architectures it's the boot loader's responsibility.)

I see two options here: either have this be parameterized by the arch
Kconfig files, or simply move this chunk into arch/*/Kconfig as part
of the arch-enablement patches. The latter is probably the simplest,
even if it means some replicated code.

Let me know what you think -- I can do this pretty easily while
importing, so you don't need to submit a full new patchset.

- I did a followon patch (attached) to change the ramdisk compression
search to table driven. Since I already did the followon patch, don't
worry about it.

-hpa

--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.

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>From 832edddc59b5f8d8243aca91a20fb55ed64d00fb Mon Sep 17 00:00:00 2001
From: H. Peter Anvin <hpa@zytor.com>
Date: Sun, 4 Jan 2009 14:42:52 -0800
Subject: [PATCH] init: 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: H. Peter Anvin <hpa@zytor.com>
---
init/do_mounts_rd.c | 82 +++++++++++++++++++++-----------------------------
1 files changed, 35 insertions(+), 47 deletions(-)

diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
index dcaeb1f..9c9d7db 100644
--- a/init/do_mounts_rd.c
+++ b/init/do_mounts_rd.c
@@ -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
*/
--
1.5.6.6