[PATCH] Big-endian reading/writing cramfs (vs 2.4.10)

[PATCH] Big-endian reading/writing cramfs (vs 2.4.10)

[Brad]

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A few people have expressed interest in this, and I needed it as
well.  Currently, cramfs images aren't shareable between different endian
architectures.  The documentation states the meta-data should always be
stored little endian, as the cost of swabbing would be low, but the code
doesn't do it.  We needed shareable images, so I modified inode.c,
cramfs_fs.h, and mkcramfs.h to enable a big-endian machine to swab meta
data when writing (mkcramfs.c) and reading (inode.c).  This is done with
#defined macros (the 26 bit/6 bit bitfield is kind of ugly to translate),
so the code doesn't change for little-endian machines, only big-endian.
I tested reading le on be, reading a be-written le image on le, etc...

This is a patch against 2.4.10.

-Brad Bozarth




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--- 2.4.10/include/linux/cramfs_fs.h	Thu Jul 19 16:14:53 2001
+++ current/include/linux/cramfs_fs.h	Thu Sep 27 17:36:57 2001
@@ -9,7 +9,12 @@
 
 #endif
 
+#if (defined(BYTE_ORDER) && BYTE_ORDER == BIG_ENDIAN) || defined(__MIPSEB__)
+#define CRAMFS_MAGIC		0x453dcd28	/* endian reversed magic */
+#else
 #define CRAMFS_MAGIC		0x28cd3d45	/* some random number */
+#endif
+
 #define CRAMFS_SIGNATURE	"Compressed ROMFS"
 
 /*
@@ -80,6 +85,40 @@
  * changed to test super.future instead.
  */
 #define CRAMFS_SUPPORTED_FLAGS (0x7ff)
+
+/* 
+ * Since cramfs (according to docs) should always be stored little endian, 
+ * provide macros to swab the bitfields (mkcramfs uses this file too). 
+ */
+#if (defined(BYTE_ORDER) && BYTE_ORDER == BIG_ENDIAN) || defined(__MIPSEB__)
+
+#define CRAM_SWAB_16(x)	( ( (0x0000FF00 & (x)) >> 8   ) | \
+			  ( (0x000000FF & (x)) << 8 ) )
+#define CRAM_SWAB_24(x)	( ( (0x00FF0000 & (x)) >> 16 ) | \
+			  ( (0x0000FF00 & (x))       ) | \
+			  ( (0x000000FF & (x)) << 16 ) )
+#define CRAM_SWAB_32(x)	( ( (0xFF000000 & (x)) >> 24 ) | \
+			  ( (0x00FF0000 & (x)) >> 8  ) | \
+			  ( (0x0000FF00 & (x)) << 8  ) | \
+			  ( (0x000000FF & (x)) << 24 ) )
+#define GET_CRAM_NAMELEN(x) (((u8*)(x))[8] & 63)
+#define GET_CRAM_OFFSET(x)  ((CRAM_SWAB_24(((u32*)(x))[2] & 0x00FFFFFF)<<2) | \
+			                 ((((u32*)(x))[2] & 0xC0000000)>>30) )
+#define SET_CRAM_OFFSET(x,y)   ( ((u32*)(x))[2] = (((y)&3)<<30) | \
+				 CRAM_SWAB_24( ( ((y) & 0x03FFFFFF) >> 2) ) | \
+				 (((u32)(((u8*)(x))[8] & 0x3F)) << 24) )
+#define SET_CRAM_NAMELEN(x,y)	( ((u8*)(x))[8] = ( ((0x3F & (y))) | \
+						    (0xC0 & ((u8*)(x))[8]) ) )
+
+#else
+#define CRAM_SWAB_16(x)		(x)
+#define CRAM_SWAB_24(x)		(x)
+#define CRAM_SWAB_32(x)		(x)
+#define GET_CRAM_NAMELEN(x)	((x)->namelen)
+#define GET_CRAM_OFFSET(x)	((x)->offset)
+#define SET_LE_OFFSET(x,y)	((x)->offset = y)
+#define SET_LE_NAMELEN(x,y)	((x)->namelen = y)
+#endif
 
 /* Uncompression interfaces to the underlying zlib */
 int cramfs_uncompress_block(void *dst, int dstlen, void *src, int srclen);
--- 2.4.10/fs/cramfs/inode.c	Mon Aug 27 07:53:49 2001
+++ current/fs/cramfs/inode.c	Fri Sep 28 14:01:53 2001
@@ -35,7 +35,7 @@
 
 /* These two macros may change in future, to provide better st_ino
    semantics. */
-#define CRAMINO(x)	((x)->offset?(x)->offset<<2:1)
+#define CRAMINO(x)	(GET_CRAM_OFFSET(x) ? GET_CRAM_OFFSET(x)<<2 : 1)
 #define OFFSET(x)	((x)->i_ino)
 
 static struct inode *get_cramfs_inode(struct super_block *sb, struct cramfs_inode * cramfs_inode)
@@ -43,9 +43,9 @@
 	struct inode * inode = new_inode(sb);
 
 	if (inode) {
-		inode->i_mode = cramfs_inode->mode;
-		inode->i_uid = cramfs_inode->uid;
-		inode->i_size = cramfs_inode->size;
+		inode->i_mode = CRAM_SWAB_16(cramfs_inode->mode);
+		inode->i_uid = CRAM_SWAB_16(cramfs_inode->uid);
+		inode->i_size = CRAM_SWAB_24(cramfs_inode->size);
 		inode->i_blocks = (cramfs_inode->size - 1) / 512 + 1;
 		inode->i_blksize = PAGE_CACHE_SIZE;
 		inode->i_gid = cramfs_inode->gid;
@@ -66,7 +66,8 @@
 			inode->i_data.a_ops = &cramfs_aops;
 		} else {
 			inode->i_size = 0;
-			init_special_inode(inode, inode->i_mode, cramfs_inode->size);
+			init_special_inode(inode, inode->i_mode, 
+					   CRAM_SWAB_24(cramfs_inode->size));
 		}
 	}
 	return inode;
@@ -219,11 +220,11 @@
 	}
 
 	/* Check that the root inode is in a sane state */
-	if (!S_ISDIR(super.root.mode)) {
+	if (!S_ISDIR(CRAM_SWAB_16(super.root.mode))) {
 		printk(KERN_ERR "cramfs: root is not a directory\n");
 		goto out;
 	}
-	root_offset = super.root.offset << 2;
+	root_offset = GET_CRAM_OFFSET(&(super.root)) << 2;
 	if (super.flags & CRAMFS_FLAG_FSID_VERSION_2) {
 		sb->CRAMFS_SB_SIZE=super.size;
 		sb->CRAMFS_SB_BLOCKS=super.fsid.blocks;
@@ -299,7 +300,7 @@
 		 * and the name padded out to 4-byte boundaries
 		 * with zeroes.
 		 */
-		namelen = de->namelen << 2;
+		namelen = GET_CRAM_NAMELEN(de) << 2;
 		nextoffset = offset + sizeof(*de) + namelen;
 		for (;;) {
 			if (!namelen)
@@ -308,7 +309,8 @@
 				break;
 			namelen--;
 		}
-		error = filldir(dirent, name, namelen, offset, CRAMINO(de), de->mode >> 12);
+		error = filldir(dirent, name, namelen, offset, CRAMINO(de), 
+				CRAM_SWAB_16(de->mode) >> 12);
 		if (error)
 			break;
 
@@ -339,7 +341,7 @@
 		if (sorted && (dentry->d_name.name[0] < name[0]))
 			break;
 
-		namelen = de->namelen << 2;
+		namelen = GET_CRAM_NAMELEN(de) << 2;
 		offset += sizeof(*de) + namelen;
 
 		/* Quick check that the name is roughly the right length */
@@ -385,9 +387,10 @@
 
 		start_offset = OFFSET(inode) + maxblock*4;
 		if (page->index)
-			start_offset = *(u32 *) cramfs_read(sb, blkptr_offset-4, 4);
-		compr_len = (*(u32 *) cramfs_read(sb, blkptr_offset, 4)
-			     - start_offset);
+			start_offset = CRAM_SWAB_32(*(u32 *) 
+				        cramfs_read(sb, blkptr_offset - 4, 4));
+		compr_len = CRAM_SWAB_32(*(u32 *)
+			     cramfs_read(sb, blkptr_offset, 4)) - start_offset;
 		pgdata = kmap(page);
 		if (compr_len == 0)
 			; /* hole */
--- 2.4.10/scripts/cramfs/mkcramfs.c	Thu Jul 19 16:14:53 2001
+++ current/scripts/cramfs/mkcramfs.c	Fri Sep 28 14:15:37 2001
@@ -317,19 +317,20 @@
 		offset += opt_pad;
 	}
 
-	super->magic = CRAMFS_MAGIC;
-	super->flags = CRAMFS_FLAG_FSID_VERSION_2 | CRAMFS_FLAG_SORTED_DIRS;
+	super->magic = CRAMFS_MAGIC; /* #defined correctly on both endians */
+	super->flags = CRAM_SWAB_32(CRAMFS_FLAG_FSID_VERSION_2 | 
+				    CRAMFS_FLAG_SORTED_DIRS);
 	if (opt_holes)
-		super->flags |= CRAMFS_FLAG_HOLES;
+		super->flags |= CRAM_SWAB_32(CRAMFS_FLAG_HOLES);
 	if (image_length > 0)
-		super->flags |= CRAMFS_FLAG_SHIFTED_ROOT_OFFSET;
-	super->size = size;
+		super->flags |= CRAM_SWAB_32(CRAMFS_FLAG_SHIFTED_ROOT_OFFSET);
+	super->size = CRAM_SWAB_24(size);
 	memcpy(super->signature, CRAMFS_SIGNATURE, sizeof(super->signature));
 
-	super->fsid.crc = crc32(0L, Z_NULL, 0);
-	super->fsid.edition = opt_edition;
-	super->fsid.blocks = total_blocks;
-	super->fsid.files = total_nodes;
+	super->fsid.crc = CRAM_SWAB_32(crc32(0L, Z_NULL, 0));
+	super->fsid.edition = CRAM_SWAB_32(opt_edition);
+	super->fsid.blocks = CRAM_SWAB_32(total_blocks);
+	super->fsid.files = CRAM_SWAB_32(total_nodes);
 
 	memset(super->name, 0x00, sizeof(super->name));
 	if (opt_name)
@@ -337,11 +338,11 @@
 	else
 		strncpy(super->name, "Compressed", sizeof(super->name));
 
-	super->root.mode = root->mode;
-	super->root.uid = root->uid;
+	super->root.mode = CRAM_SWAB_16(root->mode);
+	super->root.uid = CRAM_SWAB_16(root->uid);
 	super->root.gid = root->gid;
-	super->root.size = root->size;
-	super->root.offset = offset >> 2;
+	super->root.size = CRAM_SWAB_24(root->size);
+	SET_CRAM_OFFSET(&(super->root), offset >> 2);
 
 	return offset;
 }
@@ -356,7 +357,7 @@
 		fprintf(stderr, "filesystem too big.  Exiting.\n");
 		exit(8);
 	}
-	inode->offset = (offset >> 2);
+	SET_CRAM_OFFSET(inode, offset >> 2);
 }
 
 
@@ -379,10 +380,10 @@
 
 			entry->dir_offset = offset;
 
-			inode->mode = entry->mode;
-			inode->uid = entry->uid;
+			inode->mode = CRAM_SWAB_16(entry->mode);
+			inode->uid = CRAM_SWAB_16(entry->uid);
 			inode->gid = entry->gid;
-			inode->size = entry->size;
+			inode->size = CRAM_SWAB_24(entry->size);
 			inode->offset = 0;
 			/* Non-empty directories, regfiles and symlinks will
 			   write over inode->offset later. */
@@ -395,7 +396,7 @@
 				*(base + offset + len) = '\0';
 				len++;
 			}
-			inode->namelen = len >> 2;
+			SET_CRAM_NAMELEN(inode, len >> 2);
 			offset += len;
 
 			/* TODO: this may get it wrong for chars >= 0x80.
@@ -503,7 +504,7 @@
 			exit(8);
 		}
 
-		*(u32 *) (base + offset) = curr;
+		*(u32 *) (base + offset) = CRAM_SWAB_32(curr);
 		offset += 4;
 	} while (size);
 

Re: [PATCH] Big-endian reading/writing cramfs (vs 2.4.10)

[Andreas Dilger]

On Sep 28, 2001  14:58 -0700, Brad wrote:
> +#define CRAM_SWAB_16(x)	( ( (0x0000FF00 & (x)) >> 8   ) | \
> +			  ( (0x000000FF & (x)) << 8 ) )

Why not just use the well-defined le16_to_cpu() and le32_to_cpu() macros?

Cheers, Andreas
--
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert

Re: [PATCH] Big-endian reading/writing cramfs (vs 2.4.10)

[Brad Bozarth]

> On Sep 28, 2001  14:58 -0700, Brad wrote:
> > +#define CRAM_SWAB_16(x)	( ( (0x0000FF00 & (x)) >> 8   ) | \
> > +			  ( (0x000000FF & (x)) << 8 ) )
>
> Why not just use the well-defined le16_to_cpu() and le32_to_cpu() macros?

I did, originally... And it worked in inode.c, but I couldn't get mkcramfs
to compile using those macros.  It's outside of __KERNEL__ so I tried
using __cpu_to_le32.  The following error occurred:

/tmp/ccoK4KS0.o: In function `write_superblock':
mkcramfs.c(.text+0xefc): undefined reference to `__fswab32'
collect2: ld returned 1 exit status

__fswab32 is defined in include/linux/byteorder/swab.h as:

extern __inline__ __const__ __u32 __fswab32(__u32 x)
{
	return __arch__swab32(x);
}

Can you shed some light on the error?  I used my own macros to get around
this issue and it worked, but the defined ones would be cleaner...

Thanks,
Brad Bozarth

Re: [PATCH] Big-endian reading/writing cramfs (vs 2.4.10)

[Andreas Dilger]

On Sep 28, 2001  15:54 -0700, Brad Bozarth wrote:
> > On Sep 28, 2001  14:58 -0700, Brad wrote:
> > > +#define CRAM_SWAB_16(x)	( ( (0x0000FF00 & (x)) >> 8   ) | \
> > > +			  ( (0x000000FF & (x)) << 8 ) )
> >
> > Why not just use the well-defined le16_to_cpu() and le32_to_cpu() macros?
> 
> I did, originally... And it worked in inode.c, but I couldn't get mkcramfs
> to compile using those macros.  It's outside of __KERNEL__ so I tried
> using __cpu_to_le32.  The following error occurred:

I didn't realize that the header was also used in user-space.  I would
still use the le32_to_cpu() style macros in the code, but only define
macros of your own if the kernel ones were not defined, using either
#ifndef __KERNEL__ or #ifndef le32_to_cpu, or both.

This way, you get the benefit of the fast asm-based instructions in
the kernel, and you only use the slow ones in user-space (mkcramfs)
where you don't really care.

Cheers, Andreas
--
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert