/*
   * fs/logfs/dev_mtd.c	- Device access methods for MTD
   *
   * As should be obvious for Linux kernel code, license is GPLv2
   *
   * Copyright (c) 2005-2008 Joern Engel <joern@logfs.org>
   */
  #include "logfs.h"
  #include <linux/completion.h>
  #include <linux/mount.h>
  #include <linux/sched.h>

  #include <linux/slab.h>

  
  #define PAGE_OFS(ofs) ((ofs) & (PAGE_SIZE-1))

  static int logfs_mtd_read(struct super_block *sb, loff_t ofs, size_t len,
  			void *buf)

  {
  	struct mtd_info *mtd = logfs_super(sb)->s_mtd;
  	size_t retlen;
  	int ret;

  	ret = mtd_read(mtd, ofs, len, &retlen, buf);

  	BUG_ON(ret == -EINVAL);
  	if (ret)
  		return ret;
  
  	/* Not sure if we should loop instead. */
  	if (retlen != len)
  		return -EIO;
  
  	return 0;
  }

  static int loffs_mtd_write(struct super_block *sb, loff_t ofs, size_t len,
  			void *buf)

  {
  	struct logfs_super *super = logfs_super(sb);
  	struct mtd_info *mtd = super->s_mtd;
  	size_t retlen;
  	loff_t page_start, page_end;
  	int ret;
  
  	if (super->s_flags & LOGFS_SB_FLAG_RO)
  		return -EROFS;
  
  	BUG_ON((ofs >= mtd->size) || (len > mtd->size - ofs));
  	BUG_ON(ofs != (ofs >> super->s_writeshift) << super->s_writeshift);
  	BUG_ON(len > PAGE_CACHE_SIZE);
  	page_start = ofs & PAGE_CACHE_MASK;
  	page_end = PAGE_CACHE_ALIGN(ofs + len) - 1;

  	ret = mtd_write(mtd, ofs, len, &retlen, buf);

  	if (ret || (retlen != len))
  		return -EIO;
  
  	return 0;
  }
  
  /*
   * For as long as I can remember (since about 2001) mtd->erase has been an
   * asynchronous interface lacking the first driver to actually use the
   * asynchronous properties.  So just to prevent the first implementor of such
   * a thing from breaking logfs in 2350, we do the usual pointless dance to
   * declare a completion variable and wait for completion before returning

   * from logfs_mtd_erase().  What an exercise in futility!

   */
  static void logfs_erase_callback(struct erase_info *ei)
  {
  	complete((struct completion *)ei->priv);
  }

  static int logfs_mtd_erase_mapping(struct super_block *sb, loff_t ofs,
  				size_t len)

  {
  	struct logfs_super *super = logfs_super(sb);
  	struct address_space *mapping = super->s_mapping_inode->i_mapping;
  	struct page *page;
  	pgoff_t index = ofs >> PAGE_SHIFT;
  
  	for (index = ofs >> PAGE_SHIFT; index < (ofs + len) >> PAGE_SHIFT; index++) {
  		page = find_get_page(mapping, index);
  		if (!page)
  			continue;
  		memset(page_address(page), 0xFF, PAGE_SIZE);
  		page_cache_release(page);
  	}
  	return 0;
  }

  static int logfs_mtd_erase(struct super_block *sb, loff_t ofs, size_t len,

  		int ensure_write)

  {
  	struct mtd_info *mtd = logfs_super(sb)->s_mtd;
  	struct erase_info ei;
  	DECLARE_COMPLETION_ONSTACK(complete);
  	int ret;
  
  	BUG_ON(len % mtd->erasesize);
  	if (logfs_super(sb)->s_flags & LOGFS_SB_FLAG_RO)
  		return -EROFS;
  
  	memset(&ei, 0, sizeof(ei));
  	ei.mtd = mtd;
  	ei.addr = ofs;
  	ei.len = len;
  	ei.callback = logfs_erase_callback;
  	ei.priv = (long)&complete;

  	ret = mtd_erase(mtd, &ei);

  	if (ret)
  		return -EIO;
  
  	wait_for_completion(&complete);
  	if (ei.state != MTD_ERASE_DONE)
  		return -EIO;

  	return logfs_mtd_erase_mapping(sb, ofs, len);

  }

  static void logfs_mtd_sync(struct super_block *sb)

  {
  	struct mtd_info *mtd = logfs_super(sb)->s_mtd;

  	mtd_sync(mtd);

  }

  static int logfs_mtd_readpage(void *_sb, struct page *page)

  {
  	struct super_block *sb = _sb;
  	int err;

  	err = logfs_mtd_read(sb, page->index << PAGE_SHIFT, PAGE_SIZE,

  			page_address(page));

  	if (err == -EUCLEAN || err == -EBADMSG) {
  		/* -EBADMSG happens regularly on power failures */

  		err = 0;
  		/* FIXME: force GC this segment */
  	}
  	if (err) {
  		ClearPageUptodate(page);
  		SetPageError(page);
  	} else {
  		SetPageUptodate(page);
  		ClearPageError(page);
  	}
  	unlock_page(page);
  	return err;
  }

  static struct page *logfs_mtd_find_first_sb(struct super_block *sb, u64 *ofs)

  {
  	struct logfs_super *super = logfs_super(sb);
  	struct address_space *mapping = super->s_mapping_inode->i_mapping;

  	filler_t *filler = logfs_mtd_readpage;

  	struct mtd_info *mtd = super->s_mtd;

  	if (!mtd_can_have_bb(mtd))

  		return NULL;
  
  	*ofs = 0;

  	while (mtd_block_isbad(mtd, *ofs)) {

  		*ofs += mtd->erasesize;
  		if (*ofs >= mtd->size)
  			return NULL;
  	}
  	BUG_ON(*ofs & ~PAGE_MASK);
  	return read_cache_page(mapping, *ofs >> PAGE_SHIFT, filler, sb);
  }

  static struct page *logfs_mtd_find_last_sb(struct super_block *sb, u64 *ofs)

  {
  	struct logfs_super *super = logfs_super(sb);
  	struct address_space *mapping = super->s_mapping_inode->i_mapping;

  	filler_t *filler = logfs_mtd_readpage;

  	struct mtd_info *mtd = super->s_mtd;

  	if (!mtd_can_have_bb(mtd))

  		return NULL;
  
  	*ofs = mtd->size - mtd->erasesize;

  	while (mtd_block_isbad(mtd, *ofs)) {

  		*ofs -= mtd->erasesize;
  		if (*ofs <= 0)
  			return NULL;
  	}
  	*ofs = *ofs + mtd->erasesize - 0x1000;
  	BUG_ON(*ofs & ~PAGE_MASK);
  	return read_cache_page(mapping, *ofs >> PAGE_SHIFT, filler, sb);
  }

  static int __logfs_mtd_writeseg(struct super_block *sb, u64 ofs, pgoff_t index,

  		size_t nr_pages)
  {
  	struct logfs_super *super = logfs_super(sb);
  	struct address_space *mapping = super->s_mapping_inode->i_mapping;
  	struct page *page;
  	int i, err;
  
  	for (i = 0; i < nr_pages; i++) {
  		page = find_lock_page(mapping, index + i);
  		BUG_ON(!page);

  		err = loffs_mtd_write(sb, page->index << PAGE_SHIFT, PAGE_SIZE,
  					page_address(page));

  		unlock_page(page);
  		page_cache_release(page);
  		if (err)
  			return err;
  	}
  	return 0;
  }

  static void logfs_mtd_writeseg(struct super_block *sb, u64 ofs, size_t len)

  {
  	struct logfs_super *super = logfs_super(sb);
  	int head;
  
  	if (super->s_flags & LOGFS_SB_FLAG_RO)
  		return;
  
  	if (len == 0) {
  		/* This can happen when the object fit perfectly into a
  		 * segment, the segment gets written per sync and subsequently
  		 * closed.
  		 */
  		return;
  	}
  	head = ofs & (PAGE_SIZE - 1);
  	if (head) {
  		ofs -= head;
  		len += head;
  	}
  	len = PAGE_ALIGN(len);

  	__logfs_mtd_writeseg(sb, ofs, ofs >> PAGE_SHIFT, len >> PAGE_SHIFT);

  }

  static void logfs_mtd_put_device(struct logfs_super *s)

  {

  	put_mtd_device(s->s_mtd);

  }

  static int logfs_mtd_can_write_buf(struct super_block *sb, u64 ofs)

  {
  	struct logfs_super *super = logfs_super(sb);
  	void *buf;
  	int err;
  
  	buf = kmalloc(super->s_writesize, GFP_KERNEL);
  	if (!buf)
  		return -ENOMEM;

  	err = logfs_mtd_read(sb, ofs, super->s_writesize, buf);

  	if (err)
  		goto out;
  	if (memchr_inv(buf, 0xff, super->s_writesize))
  		err = -EIO;
  	kfree(buf);
  out:
  	return err;
  }

  static const struct logfs_device_ops mtd_devops = {

  	.find_first_sb	= logfs_mtd_find_first_sb,
  	.find_last_sb	= logfs_mtd_find_last_sb,
  	.readpage	= logfs_mtd_readpage,
  	.writeseg	= logfs_mtd_writeseg,
  	.erase		= logfs_mtd_erase,
  	.can_write_buf	= logfs_mtd_can_write_buf,
  	.sync		= logfs_mtd_sync,
  	.put_device	= logfs_mtd_put_device,

  };

  int logfs_get_sb_mtd(struct logfs_super *s, int mtdnr)

  {

  	struct mtd_info *mtd = get_mtd_device(NULL, mtdnr);

  	if (IS_ERR(mtd))

  		return PTR_ERR(mtd);

  
  	s->s_bdev = NULL;
  	s->s_mtd = mtd;
  	s->s_devops = &mtd_devops;

  	return 0;

  }