text: // SPDX-License-Identifier: GPL-2.0-or-later
  /*
   * Direct MTD block device access
   *
   * Copyright © 1999-2010 David Woodhouse <dwmw2@infradead.org>
   * Copyright © 2000-2003 Nicolas Pitre <nico@fluxnic.net>
   */
  
  #include <linux/fs.h>
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/sched.h>
  #include <linux/slab.h>
  #include <linux/types.h>
  #include <linux/vmalloc.h>
  
  #include <linux/mtd/mtd.h>
  #include <linux/mtd/blktrans.h>
  #include <linux/mutex.h>
  #include <linux/major.h>
  
  
  struct mtdblk_dev {
  	struct mtd_blktrans_dev mbd;
  	int count;
  	struct mutex cache_mutex;
  	unsigned char *cache_data;
  	unsigned long cache_offset;
  	unsigned int cache_size;
  	enum { STATE_EMPTY, STATE_CLEAN, STATE_DIRTY } cache_state;
  };
  
  /*
   * Cache stuff...
   *
   * Since typical flash erasable sectors are much larger than what Linux's
   * buffer cache can handle, we must implement read-modify-write on flash
   * sectors for each block write requests.  To avoid over-erasing flash sectors
   * and to speed things up, we locally cache a whole flash sector while it is
   * being written to until a different sector is required.
   */
  
  static int erase_write (struct mtd_info *mtd, unsigned long pos,
  			unsigned int len, const char *buf)
  {
  	struct erase_info erase;
  	size_t retlen;
  	int ret;
  
  	/*
  	 * First, let's erase the flash block.
  	 */
  	erase.addr = pos;
  	erase.len = len;
  
  	ret = mtd_erase(mtd, &erase);
  	if (ret) {
  		printk (KERN_WARNING "mtdblock: erase of region [0x%lx, 0x%x] "
  				     "on \"%s\" failed\n",
  			pos, len, mtd->name);
  		return ret;
  	}
  
  	/*
  	 * Next, write the data to flash.
  	 */
  
  	ret = mtd_write(mtd, pos, len, &retlen, buf);
  	if (ret)
  		return ret;
  	if (retlen != len)
  		return -EIO;
  	return 0;
  }
  
  
  static int write_cached_data (struct mtdblk_dev *mtdblk)
  {
  	struct mtd_info *mtd = mtdblk->mbd.mtd;
  	int ret;
  
  	if (mtdblk->cache_state != STATE_DIRTY)
  		return 0;
  
  	pr_debug("mtdblock: writing cached data for \"%s\" "
  			"at 0x%lx, size 0x%x\n", mtd->name,
  			mtdblk->cache_offset, mtdblk->cache_size);
  
  	ret = erase_write (mtd, mtdblk->cache_offset,
  			   mtdblk->cache_size, mtdblk->cache_data);
  
  	/*
  	 * Here we could arguably set the cache state to STATE_CLEAN.
  	 * However this could lead to inconsistency since we will not
  	 * be notified if this content is altered on the flash by other
  	 * means.  Let's declare it empty and leave buffering tasks to
  	 * the buffer cache instead.
  	 *
  	 * If this cache_offset points to a bad block, data cannot be
  	 * written to the device. Clear cache_state to avoid writing to
  	 * bad blocks repeatedly.
  	 */
  	if (ret == 0 || ret == -EIO)
  		mtdblk->cache_state = STATE_EMPTY;
  	return ret;
  }
  
  
  static int do_cached_write (struct mtdblk_dev *mtdblk, unsigned long pos,
  			    int len, const char *buf)
  {
  	struct mtd_info *mtd = mtdblk->mbd.mtd;
  	unsigned int sect_size = mtdblk->cache_size;
  	size_t retlen;
  	int ret;
  
  	pr_debug("mtdblock: write on \"%s\" at 0x%lx, size 0x%x\n",
  		mtd->name, pos, len);
  
  	if (!sect_size)
  		return mtd_write(mtd, pos, len, &retlen, buf);
  
  	while (len > 0) {
  		unsigned long sect_start = (pos/sect_size)*sect_size;
  		unsigned int offset = pos - sect_start;
  		unsigned int size = sect_size - offset;
  		if( size > len )
  			size = len;
  
  		if (size == sect_size) {
  			/*
  			 * We are covering a whole sector.  Thus there is no
  			 * need to bother with the cache while it may still be
  			 * useful for other partial writes.
  			 */
  			ret = erase_write (mtd, pos, size, buf);
  			if (ret)
  				return ret;
  		} else {
  			/* Partial sector: need to use the cache */
  
  			if (mtdblk->cache_state == STATE_DIRTY &&
  			    mtdblk->cache_offset != sect_start) {
  				ret = write_cached_data(mtdblk);
  				if (ret)
  					return ret;
  			}
  
  			if (mtdblk->cache_state == STATE_EMPTY ||
  			    mtdblk->cache_offset != sect_start) {
  				/* fill the cache with the current sector */
  				mtdblk->cache_state = STATE_EMPTY;
  				ret = mtd_read(mtd, sect_start, sect_size,
  					       &retlen, mtdblk->cache_data);
  				if (ret)
  					return ret;
  				if (retlen != sect_size)
  					return -EIO;
  
  				mtdblk->cache_offset = sect_start;
  				mtdblk->cache_size = sect_size;
  				mtdblk->cache_state = STATE_CLEAN;
  			}
  
  			/* write data to our local cache */
  			memcpy (mtdblk->cache_data + offset, buf, size);
  			mtdblk->cache_state = STATE_DIRTY;
  		}
  
  		buf += size;
  		pos += size;
  		len -= size;
  	}
  
  	return 0;
  }
  
  
  static int do_cached_read (struct mtdblk_dev *mtdblk, unsigned long pos,
  			   int len, char *buf)
  {
  	struct mtd_info *mtd = mtdblk->mbd.mtd;
  	unsigned int sect_size = mtdblk->cache_size;
  	size_t retlen;
  	int ret;
  
  	pr_debug("mtdblock: read on \"%s\" at 0x%lx, size 0x%x\n",
  			mtd->name, pos, len);
  
  	if (!sect_size)
  		return mtd_read(mtd, pos, len, &retlen, buf);
  
  	while (len > 0) {
  		unsigned long sect_start = (pos/sect_size)*sect_size;
  		unsigned int offset = pos - sect_start;
  		unsigned int size = sect_size - offset;
  		if (size > len)
  			size = len;
  
  		/*
  		 * Check if the requested data is already cached
  		 * Read the requested amount of data from our internal cache if it
  		 * contains what we want, otherwise we read the data directly
  		 * from flash.
  		 */
  		if (mtdblk->cache_state != STATE_EMPTY &&
  		    mtdblk->cache_offset == sect_start) {
  			memcpy (buf, mtdblk->cache_data + offset, size);
  		} else {
  			ret = mtd_read(mtd, pos, size, &retlen, buf);
  			if (ret)
  				return ret;
  			if (retlen != size)
  				return -EIO;
  		}
  
  		buf += size;
  		pos += size;
  		len -= size;
  	}
  
  	return 0;
  }
  
  static int mtdblock_readsect(struct mtd_blktrans_dev *dev,
  			      unsigned long block, char *buf)
  {
  	struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
  	return do_cached_read(mtdblk, block<<9, 512, buf);
  }
  
  static int mtdblock_writesect(struct mtd_blktrans_dev *dev,
  			      unsigned long block, char *buf)
  {
  	struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
  	if (unlikely(!mtdblk->cache_data && mtdblk->cache_size)) {
  		mtdblk->cache_data = vmalloc(mtdblk->mbd.mtd->erasesize);
  		if (!mtdblk->cache_data)
  			return -EINTR;
  		/* -EINTR is not really correct, but it is the best match
  		 * documented in man 2 write for all cases.  We could also
  		 * return -EAGAIN sometimes, but why bother?
  		 */
  	}
  	return do_cached_write(mtdblk, block<<9, 512, buf);
  }
  
  static int mtdblock_open(struct mtd_blktrans_dev *mbd)
  {
  	struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);
  
  	pr_debug("mtdblock_open\n");
  
  	if (mtdblk->count) {
  		mtdblk->count++;
  		return 0;
  	}
  
  	/* OK, it's not open. Create cache info for it */
  	mtdblk->count = 1;
  	mutex_init(&mtdblk->cache_mutex);
  	mtdblk->cache_state = STATE_EMPTY;
  	if (!(mbd->mtd->flags & MTD_NO_ERASE) && mbd->mtd->erasesize) {
  		mtdblk->cache_size = mbd->mtd->erasesize;
  		mtdblk->cache_data = NULL;
  	}
  
  	pr_debug("ok\n");
  
  	return 0;
  }
  
  static void mtdblock_release(struct mtd_blktrans_dev *mbd)
  {
  	struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);
  
  	pr_debug("mtdblock_release\n");
  
  	mutex_lock(&mtdblk->cache_mutex);
  	write_cached_data(mtdblk);
  	mutex_unlock(&mtdblk->cache_mutex);
  
  	if (!--mtdblk->count) {
  		/*
  		 * It was the last usage. Free the cache, but only sync if
  		 * opened for writing.
  		 */
  		if (mbd->file_mode & FMODE_WRITE)
  			mtd_sync(mbd->mtd);
  		vfree(mtdblk->cache_data);
  	}
  
  	pr_debug("ok\n");
  }
  
  static int mtdblock_flush(struct mtd_blktrans_dev *dev)
  {
  	struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
  	int ret;
  
  	mutex_lock(&mtdblk->cache_mutex);
  	ret = write_cached_data(mtdblk);
  	mutex_unlock(&mtdblk->cache_mutex);
  	mtd_sync(dev->mtd);
  	return ret;
  }
  
  static void mtdblock_add_mtd(struct mtd_blktrans_ops *tr, struct mtd_info *mtd)
  {
  	struct mtdblk_dev *dev = kzalloc(sizeof(*dev), GFP_KERNEL);
  
  	if (!dev)
  		return;
  
  	dev->mbd.mtd = mtd;
  	dev->mbd.devnum = mtd->index;
  
  	dev->mbd.size = mtd->size >> 9;
  	dev->mbd.tr = tr;
  
  	if (!(mtd->flags & MTD_WRITEABLE))
  		dev->mbd.readonly = 1;
  
  	if (add_mtd_blktrans_dev(&dev->mbd))
  		kfree(dev);
  }
  
  static void mtdblock_remove_dev(struct mtd_blktrans_dev *dev)
  {
  	del_mtd_blktrans_dev(dev);
  }
  
  static struct mtd_blktrans_ops mtdblock_tr = {
  	.name		= "mtdblock",
  	.major		= MTD_BLOCK_MAJOR,
  	.part_bits	= 0,
  	.blksize 	= 512,
  	.open		= mtdblock_open,
  	.flush		= mtdblock_flush,
  	.release	= mtdblock_release,
  	.readsect	= mtdblock_readsect,
  	.writesect	= mtdblock_writesect,
  	.add_mtd	= mtdblock_add_mtd,
  	.remove_dev	= mtdblock_remove_dev,
  	.owner		= THIS_MODULE,
  };
  
  module_mtd_blktrans(mtdblock_tr);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Nicolas Pitre <nico@fluxnic.net> et al.");
  MODULE_DESCRIPTION("Caching read/erase/writeback block device emulation access to MTD devices");
  