[PATCH] [MTD] BLOCK_RO: Readonly Block Device Layer Over MTD

[Konstantin Baydarov]

On Wed, 22 Nov 2006 19:56:33 +0300
Konstantin Baydarov <kbaidarov at dev.rtsoft.ru> wrote:
> 
> Corrected typo, renamed driver, got rid from redundant dependency.
> Also I've tested mtdblock_ro_bbfree as module - ok.

Renamed driver to 'romblock'. Every entry of 'mtdblock' was replaced.
Debug level in DEBUG macros was replaced by corresponding macros.

 drivers/mtd/Kconfig    |    7 ++
 drivers/mtd/Makefile   |    1 
 drivers/mtd/romblock.c |  165 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 173 insertions(+)

Index: mtd-2.6/drivers/mtd/romblock.c
===================================================================
--- /dev/null
+++ mtd-2.6/drivers/mtd/romblock.c
@@ -0,0 +1,165 @@
+/*
+ *  Readonly Block Device Layer Over MTD
+ *
+ *  (C) 2006 Baydarov Konstantin <kbaidarov at dev.rtsoft.ru>
+ *           Pantelis Antoniou <panto at intracom.gr>
+ *           David Woodhouse <dwmw2 at infradead.org>
+ *
+ *  It allows to use any filesystem on this device in
+ *  RO mode and thus gain faster mount times and better
+ *  throughput rates.
+ *
+ */
+
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/blktrans.h>
+
+struct romblock_map {
+	struct mtd_blktrans_dev dev;
+	/* block map for RO */
+	int32_t *block_map;
+	int32_t block_top;
+	int32_t block_scantop;
+};
+
+static loff_t map_over_bad_blocks(struct mtd_blktrans_dev* dev, loff_t from)
+{
+	int i, block;
+	struct mtd_info *mtd = dev->mtd;
+	struct romblock_map* dev_cont = container_of(dev, struct romblock_map, dev);
+	int32_t *block_map = dev_cont->block_map;
+	int32_t block_top = dev_cont->block_top;
+	int32_t block_scantop = dev_cont->block_scantop;
+
+	/* if no bad block checking is possible bail out */
+	if (mtd->block_isbad == NULL)
+		return from;
+
+	/* first time in */
+	if (block_map == NULL) {
+		block_top = mtd->size / mtd->erasesize;
+		block_map = kmalloc(sizeof(*block_map) * block_top, GFP_KERNEL);
+		if (block_map == NULL) {
+			printk (KERN_ERR "map_over_bad_blocks(): unable to allocate block map\n");
+			return -ENOMEM;
+		}
+		for (i = 0; i < block_top; i++)
+			block_map[i] = -1;
+
+		for (i = 0; i < block_top; i++)
+			if ((*mtd->block_isbad)(mtd, i * mtd->erasesize) == 0)
+				break;
+
+		if (i >= block_top) {
+			printk (KERN_WARNING "map_over_bad_blocks(): all blocks bad!\n");
+			return -EIO;
+		}
+		block_scantop = 0;
+		block_map[0] = i;
+
+		DEBUG(MTD_DEBUG_LEVEL0, "mtd: map %d -> %d\n", block_scantop, block_map[block_scantop]);
+	}
+
+	block = ((int)from / mtd->erasesize);
+	if (block >= block_top)
+		return (loff_t)-1;
+
+	/* scan for bad block up to where we want */
+	while (block >= block_scantop) {
+		/* find a non bad block */
+		for (i = block_map[block_scantop] + 1; i < block_top; i++)
+			if ((*mtd->block_isbad)(mtd, i * mtd->erasesize) == 0)
+				break;
+
+		/* exhausted ? */
+		if (i >= block_top) {
+			printk (KERN_WARNING "map_over_bad_blocks(): no more good blocks!\n");
+			return (loff_t)-1;
+		}
+
+		block_map[++block_scantop] = i;
+		DEBUG(MTD_DEBUG_LEVEL0, "mtd: map %d -> %d\n", block_scantop, block_map[block_scantop]);
+	}
+
+	block = block_map[(int)from / mtd->erasesize];
+	from = (block * mtd->erasesize) | ((int)from & (mtd->erasesize - 1));
+	return from;
+}
+
+static int romblock_readsect(struct mtd_blktrans_dev *dev,
+			      unsigned long block, char *buf)
+{
+	size_t retlen;
+	unsigned long from;
+
+	from = map_over_bad_blocks(dev, block<<9);
+
+	if (dev->mtd->read(dev->mtd, from, 512, &retlen, buf))
+		return 1;
+	return 0;
+}
+
+static int romblock_writesect(struct mtd_blktrans_dev *dev,
+			      unsigned long block, char *buf)
+{
+	size_t retlen;
+
+	if (dev->mtd->write(dev->mtd, (block * 512), 512, &retlen, buf))
+		return 1;
+	return 0;
+}
+
+static void romblock_add_mtd(struct mtd_blktrans_ops *tr, struct mtd_info *mtd)
+{
+	struct romblock_map *dev_cont = kmalloc(sizeof(*dev_cont), GFP_KERNEL);
+
+	if (!dev_cont)
+		return;
+
+	memset(dev_cont, 0, sizeof(*dev_cont));
+
+	dev_cont->dev.mtd = mtd;
+	dev_cont->dev.devnum = mtd->index;
+	dev_cont->dev.blksize = 512;
+	dev_cont->dev.size = mtd->size >> 9;
+	dev_cont->dev.tr = tr;
+	dev_cont->dev.readonly = 1;
+
+	add_mtd_blktrans_dev(&(dev_cont->dev));
+}
+
+static void romblock_remove_dev(struct mtd_blktrans_dev *dev)
+{
+	del_mtd_blktrans_dev(dev);
+	kfree(dev);
+}
+
+static struct mtd_blktrans_ops romblock_tr = {
+	.name		= "romblock",
+	.major		= 258,
+	.part_bits	= 0,
+	.readsect	= romblock_readsect,
+	.writesect	= romblock_writesect,
+	.add_mtd	= romblock_add_mtd,
+	.remove_dev	= romblock_remove_dev,
+	.owner		= THIS_MODULE,
+};
+
+static int __init romblock_init(void)
+{
+	return register_mtd_blktrans(&romblock_tr);
+}
+
+static void __exit romblock_exit(void)
+{
+	deregister_mtd_blktrans(&romblock_tr);
+}
+
+module_init(romblock_init);
+module_exit(romblock_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Baydarov Konstantin <kbaidarov at dev.rtsoft.ru>");
+MODULE_DESCRIPTION("Readonly Block Device Layer Over MTD");
Index: mtd-2.6/drivers/mtd/Makefile
===================================================================
--- mtd-2.6.orig/drivers/mtd/Makefile
+++ mtd-2.6/drivers/mtd/Makefile
@@ -17,6 +17,7 @@ obj-$(CONFIG_MTD_AFS_PARTS)	+= afs.o
 obj-$(CONFIG_MTD_CHAR)		+= mtdchar.o
 obj-$(CONFIG_MTD_BLOCK)		+= mtdblock.o mtd_blkdevs.o
 obj-$(CONFIG_MTD_BLOCK_RO)	+= mtdblock_ro.o mtd_blkdevs.o
+obj-$(CONFIG_MTD_BLOCK_ROMBLOCK)	+= romblock.o mtd_blkdevs.o
 obj-$(CONFIG_FTL)		+= ftl.o mtd_blkdevs.o
 obj-$(CONFIG_NFTL)		+= nftl.o mtd_blkdevs.o
 obj-$(CONFIG_INFTL)		+= inftl.o mtd_blkdevs.o
Index: mtd-2.6/drivers/mtd/Kconfig
===================================================================
--- mtd-2.6.orig/drivers/mtd/Kconfig
+++ mtd-2.6/drivers/mtd/Kconfig
@@ -197,6 +197,13 @@ config MTD_BLOCK_RO
 	  You do not need this option for use with the DiskOnChip devices. For
 	  those, enable NFTL support (CONFIG_NFTL) instead.
 
+config MTD_BLOCK_ROMBLOCK
+	tristate "Readonly Block Device Layer Over MTD"
+	depends on MTD_BLOCK!=y && MTD
+	help
+	  Same as readonly block driver, but this allow you to mount read-only file
+	  systems from an MTD device, containing bad blocks.
+
 config FTL
 	tristate "FTL (Flash Translation Layer) support"
 	depends on MTD && BLOCK