blkmtd.c

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/* 
 * $Id: blkmtd.c,v 1.3 2001/10/02 15:33:20 dwmw2 Exp $
 * blkmtd.c - use a block device as a fake MTD
 *
 * Author: Simon Evans <[e-mail]>
 *
 * Copyright (C) 2001 Simon Evans <[e-mail]>
 * 
 * Licence: GPL
 *
 * How it works:
 *       The driver uses raw/io to read/write the device and the page
 *       cache to cache access. Writes update the page cache with the
 *       new data but make a copy of the new page(s) and then a kernel
 *       thread writes pages out to the device in the background. This
 *       ensures tht writes are order even if a page is updated twice.
 *       Also, since pages in the page cache are never marked as dirty,
 *       we dont have to worry about writepage() being called on some 
 *       random page which may not be in the write order.
 * 
 *       Erases are handled like writes, so the callback is called after
 *       the page cache has been updated. Sync()ing will wait until it is 
 *       all done.
 *
 *       It can be loaded Read-Only to prevent erases and writes to the 
 *       medium.
 *
 * Todo:
 *       Make the write queue size dynamic so this it is not too big on
 *       small memory systems and too small on large memory systems.
 * 
 *       Page cache usage may still be a bit wrong. Check we are doing
 *       everything proberly.
 * 
 *       Somehow allow writes to dirty the page cache so we dont use too
 *       much memory making copies of outgoing pages. Need to handle case
 *       where page x is written to, then page y, then page x again before
 *       any of them have been committed to disk.
 * 
 *       Reading should read multiple pages at once rather than using 
 *       readpage() for each one. This is easy and will be fixed asap.
 *
 *       Dont run the write_thread if readonly. This is also easy and will
 *       be fixed asap.
 * 
 *       Even though the multiple erase regions are used if the default erase
 *       block size doesnt match the device properly, erases currently wont
 *       work on the last page if it is not a full page.
 */

#include <linux/config.h>
#include <linux/module.h>

#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/iobuf.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/mtd/compatmac.h>
#include <linux/mtd/mtd.h>

/* Default erase size in K, always make it a multiple of PAGE_SIZE */
#define CONFIG_MTD_BLKDEV_ERASESIZE 128
#define VERSION "1.1"
extern int *blk_size[];
extern int *blksize_size[];

/* Info for the block device */
typedef struct mtd_raw_dev_data_s {
  struct block_device *binding;
  int sector_size, sector_bits, total_sectors;
  size_t totalsize;
  int readonly;
  struct address_space as;
  struct file *file;
} mtd_raw_dev_data_t;

/* Info for each queue item in the write queue */
typedef struct mtdblkdev_write_queue_s {
  mtd_raw_dev_data_t *rawdevice;
  struct page **pages;
  int pagenr;
  int pagecnt;
  int iserase;
} mtdblkdev_write_queue_t;


/* Static info about the MTD, used in cleanup_module */
static struct mtd_info *mtd_info;

/* Write queue fixed size */
#define WRITE_QUEUE_SZ 512

/* Storage for the write queue */
static mtdblkdev_write_queue_t write_queue[WRITE_QUEUE_SZ];
static int volatile write_queue_head;
static int volatile write_queue_tail;
static int volatile write_queue_cnt;
static spinlock_t mbd_writeq_lock = SPIN_LOCK_UNLOCKED;

/* Tell the write thread to finish */
static volatile int write_task_finish = 0;

/* ipc with the write thread */
#if LINUX_VERSION_CODE > 0x020300
static DECLARE_MUTEX_LOCKED(thread_sem);
static DECLARE_WAIT_QUEUE_HEAD(thr_wq);
static DECLARE_WAIT_QUEUE_HEAD(mtbd_sync_wq);
#else
static struct semaphore thread_sem = MUTEX_LOCKED;
DECLARE_WAIT_QUEUE_HEAD(thr_wq);
DECLARE_WAIT_QUEUE_HEAD(mtbd_sync_wq);
#endif



/* Module parameters passed by insmod/modprobe */
char *device;    /* the block device to use */
int erasesz;     /* optional default erase size */
int ro;          /* optional read only flag */
int bs;          /* optionally force the block size (avoid using) */
int count;       /* optionally force the block count (avoid using) */

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Simon Evans <[e-mail]>");
MODULE_DESCRIPTION("Emulate an MTD using a block device");
MODULE_PARM(device, "s");
MODULE_PARM_DESC(device, "block device to use");
MODULE_PARM(erasesz, "i");
MODULE_PARM_DESC(erasesz, "optional erase size to use in KB. eg 4=4K.");
MODULE_PARM(ro, "i");
MODULE_PARM_DESC(ro, "1=Read only, writes and erases cause errors");
MODULE_PARM(bs, "i");
MODULE_PARM_DESC(bs, "force the block size in bytes");
MODULE_PARM(count, "i");
MODULE_PARM_DESC(count, "force the block count");
#endif



/* Page cache stuff */

/* writepage() - should never be called - catch it anyway */
static int blkmtd_writepage(struct page *page)
{
  printk("blkmtd: writepage called!!!\n");
  return -EIO;
}


/* readpage() - reads one page from the block device */                 
static int blkmtd_readpage(struct file *file, struct page *page)
{  
  int err;
  int sectornr, sectors, i;
  struct kiobuf *iobuf;
  mtd_raw_dev_data_t *rawdevice = (mtd_raw_dev_data_t *)file->private_data;
  kdev_t dev;

  if(!rawdevice) {
    printk("blkmtd: readpage: PANIC file->private_data == NULL\n");
    return -EIO;
  }
  dev = to_kdev_t(rawdevice->binding->bd_dev);

  DEBUG(2, "blkmtd: readpage called, dev = `%s' page = %p index = %ld\n",
	bdevname(dev), page, page->index);

  if(Page_Uptodate(page)) {
    DEBUG(1, "blkmtd: readpage page %ld is already upto date\n", page->index);
    UnlockPage(page);
    return 0;
  }

  ClearPageUptodate(page);
  ClearPageError(page);

  /* see if page is in the outgoing write queue */
  spin_lock(&mbd_writeq_lock);
  if(write_queue_cnt) {
    int i = write_queue_tail;
    while(i != write_queue_head) {
      mtdblkdev_write_queue_t *item = &write_queue[i];
      if(page->index >= item->pagenr && page->index < item->pagenr+item->pagecnt) {
	/* yes it is */
	int index = item->pagenr - page->index;
	DEBUG(1, "blkmtd: readpage: found page %ld in outgoing write queue\n",
	      page->index);
	if(item->iserase) {
	  memset(page_address(page), 0xff, PAGE_SIZE);
	} else {
	  memcpy(page_address(page), page_address(item->pages[index]), PAGE_SIZE);
	}
	SetPageUptodate(page);
	flush_dcache_page(page);
	UnlockPage(page);
	spin_unlock(&mbd_writeq_lock);
	return 0;
      }
      i++;
      i %= WRITE_QUEUE_SZ;
    }
  }
  spin_unlock(&mbd_writeq_lock);


  DEBUG(3, "blkmtd: readpage: getting kiovec\n");
  err = alloc_kiovec(1, &iobuf);
  if (err) {
    return err;
  }
  iobuf->offset = 0;
  iobuf->nr_pages = 1;
  iobuf->length = PAGE_SIZE;
  iobuf->locked = 1;
  iobuf->maplist[0] = page;
  sectornr = page->index << (PAGE_SHIFT - rawdevice->sector_bits);
  sectors = 1 << (PAGE_SHIFT - rawdevice->sector_bits);
  DEBUG(3, "blkmtd: readpage: sectornr = %d sectors = %d\n", sectornr, sectors);
  for(i = 0; i < sectors; i++) {
    iobuf->blocks[i] = sectornr++;
  }

  DEBUG(3, "bklmtd: readpage: starting brw_kiovec\n");
  err = brw_kiovec(READ, 1, &iobuf, dev, iobuf->blocks, rawdevice->sector_size);
  DEBUG(3, "blkmtd: readpage: finished, err = %d\n", err);
  iobuf->locked = 0;
  free_kiovec(1, &iobuf);
  if(err != PAGE_SIZE) {
    printk("blkmtd: readpage: error reading page %ld\n", page->index);
    memset(page_address(page), 0, PAGE_SIZE);
    SetPageError(page);
    err = -EIO;
  } else {
    DEBUG(3, "blkmtd: readpage: setting page upto date\n");
    SetPageUptodate(page);
    err = 0;
  }
  flush_dcache_page(page);
  UnlockPage(page);
  DEBUG(2, "blkmtd: readpage: finished, err = %d\n", err);
  return 0;
}

                    
static struct address_space_operations blkmtd_aops = {
  writepage:     blkmtd_writepage,
  readpage:      blkmtd_readpage,
}; 


/* This is the kernel thread that empties the write queue to disk */
static int write_queue_task(void *data)
{
  int err;
  struct task_struct *tsk = current;
  struct kiobuf *iobuf;

  DECLARE_WAITQUEUE(wait, tsk);
  DEBUG(1, "blkmtd: writetask: starting (pid = %d)\n", tsk->pid);
  daemonize();
  strcpy(tsk->comm, "blkmtdd");
  tsk->tty = NULL;
  spin_lock_irq(&tsk->sigmask_lock);
  sigfillset(&tsk->blocked);
  recalc_sigpending(tsk);
  spin_unlock_irq(&tsk->sigmask_lock);
  exit_sighand(tsk);

  if(alloc_kiovec(1, &iobuf))
    return 0;
  DEBUG(2, "blkmtd: writetask: entering main loop\n");
  add_wait_queue(&thr_wq, &wait);

  while(1) {
    spin_lock(&mbd_writeq_lock);

    if(!write_queue_cnt) {
      /* If nothing in the queue, wake up anyone wanting to know when there
	 is space in the queue then sleep for 2*HZ */
      spin_unlock(&mbd_writeq_lock);
      DEBUG(3, "blkmtd: writetask: queue empty\n");
      if(waitqueue_active(&mtbd_sync_wq))
	 wake_up(&mtbd_sync_wq);
      interruptible_sleep_on_timeout(&thr_wq, 2*HZ);
      DEBUG(3, "blkmtd: writetask: woken up\n");
      if(write_task_finish)
	break;
    } else {
      /* we have stuff to write */
      mtdblkdev_write_queue_t *item = &write_queue[write_queue_tail];
      struct page **pages = item->pages;
      int pagecnt = item->pagecnt;
      int pagenr = item->pagenr;
      int i;
      int max_sectors = KIO_MAX_SECTORS >> (item->rawdevice->sector_bits - 9);
      kdev_t dev = to_kdev_t(item->rawdevice->binding->bd_dev);
  

      DEBUG(3, "blkmtd: writetask: got %d queue items\n", write_queue_cnt);
      set_current_state(TASK_RUNNING);
      spin_unlock(&mbd_writeq_lock);

      DEBUG(2, "blkmtd: write_task: writing pagenr = %d pagecnt = %d", 
	    item->pagenr, item->pagecnt);

      iobuf->offset = 0;
      iobuf->locked = 1;

      /* Loop through all the pages to be written in the queue item, remembering
	 we can only write KIO_MAX_SECTORS at a time */
	 
      while(pagecnt) {
	int sectornr = pagenr << (PAGE_SHIFT - item->rawdevice->sector_bits);
	int sectorcnt = pagecnt << (PAGE_SHIFT - item->rawdevice->sector_bits);
	int cursectors = (sectorcnt < max_sectors) ? sectorcnt : max_sectors;
	int cpagecnt = (cursectors << item->rawdevice->sector_bits) + PAGE_SIZE-1;
	cpagecnt >>= PAGE_SHIFT;
	
	for(i = 0; i < cpagecnt; i++) 
	    iobuf->maplist[i] = *(pages++);
	
	for(i = 0; i < cursectors; i++) {
	  iobuf->blocks[i] = sectornr++;
	}
	
	iobuf->nr_pages = cpagecnt;
	iobuf->length = cursectors << item->rawdevice->sector_bits;
	DEBUG(3, "blkmtd: write_task: about to kiovec\n");
	err = brw_kiovec(WRITE, 1, &iobuf, dev, iobuf->blocks, item->rawdevice->sector_size);
	DEBUG(3, "bklmtd: write_task: done, err = %d\n", err);
	if(err != (cursectors << item->rawdevice->sector_bits)) {
	  /* if an error occured - set this to exit the loop */
	  pagecnt = 0;
	} else {
	  pagenr += cpagecnt;
	  pagecnt -= cpagecnt;
	}
      }

      /* free up the pages used in the write and list of pages used in the write
	 queue item */
      iobuf->locked = 0;
      spin_lock(&mbd_writeq_lock);
      write_queue_cnt--;
      write_queue_tail++;
      write_queue_tail %= WRITE_QUEUE_SZ;
      for(i = 0 ; i < item->pagecnt; i++) {
	UnlockPage(item->pages[i]);
	__free_pages(item->pages[i], 0);
      }
      kfree(item->pages);
      item->pages = NULL;
      spin_unlock(&mbd_writeq_lock);
      /* Tell others there is some space in the write queue */
      if(waitqueue_active(&mtbd_sync_wq))
	wake_up(&mtbd_sync_wq);
    }
  }
  remove_wait_queue(&thr_wq, &wait);
  DEBUG(1, "blkmtd: writetask: exiting\n");
  free_kiovec(1, &iobuf);
  /* Tell people we have exitd */
  up(&thread_sem);
  return 0;
}


/* Add a range of pages into the outgoing write queue, making copies of them */
static int queue_page_write(mtd_raw_dev_data_t *rawdevice, struct page **pages,
			    int pagenr, int pagecnt, int iserase)
{
  struct page *outpage;
  struct page **new_pages;
  mtdblkdev_write_queue_t *item;
  int i;
  DECLARE_WAITQUEUE(wait, current);
  DEBUG(2, "mtdblkdev: queue_page_write: adding pagenr = %d pagecnt = %d\n", pagenr, pagecnt);

  if(!pagecnt)
    return 0;

  if(pages == NULL)
    return -EINVAL;

  /* create a array for the list of pages */
  new_pages = kmalloc(pagecnt * sizeof(struct page *), GFP_KERNEL);
  if(new_pages == NULL)
    return -ENOMEM;

  /* make copies of the pages in the page cache */
  for(i = 0; i < pagecnt; i++) {
    outpage = alloc_pages(GFP_KERNEL, 0);
    if(!outpage) {
      while(i--) {
	UnlockPage(new_pages[i]);
	__free_pages(new_pages[i], 0);
      }
      kfree(new_pages);
      return -ENOMEM;
    }
    lock_page(outpage);
    memcpy(page_address(outpage), page_address(pages[i]), PAGE_SIZE);
    new_pages[i] = outpage;
  }

  /* wait until there is some space in the write queue */
 test_lock:
  spin_lock(&mbd_writeq_lock);
  if(write_queue_cnt == WRITE_QUEUE_SZ) {
    spin_unlock(&mbd_writeq_lock);
    DEBUG(3, "blkmtd: queue_page: Queue full\n");
    current->state = TASK_UNINTERRUPTIBLE;
    add_wait_queue(&mtbd_sync_wq, &wait);
    wake_up_interruptible(&thr_wq);
    schedule();
    current->state = TASK_RUNNING;
    remove_wait_queue(&mtbd_sync_wq, &wait);
    DEBUG(3, "blkmtd: queue_page: Queue has %d items in it\n", write_queue_cnt);
    goto test_lock;
  }

  DEBUG(3, "blkmtd: queue_write_page: qhead: %d qtail: %d qcnt: %d\n", 
	write_queue_head, write_queue_tail, write_queue_cnt);

  /* fix up the queue item */
  item = &write_queue[write_queue_head];
  item->pages = new_pages;
  item->pagenr = pagenr;
  item->pagecnt = pagecnt;
  item->rawdevice = rawdevice;
  item->iserase = iserase;

  write_queue_head++;
  write_queue_head %= WRITE_QUEUE_SZ;
  write_queue_cnt++;
  DEBUG(3, "blkmtd: queue_write_page: qhead: %d qtail: %d qcnt: %d\n", 
	write_queue_head, write_queue_tail, write_queue_cnt);
  spin_unlock(&mbd_writeq_lock);
  DEBUG(2, "blkmtd: queue_page_write: finished\n");
  return 0;
}


/* erase a specified part of the device */
static int blkmtd_erase(struct mtd_info *mtd, struct erase_info *instr)
{
  mtd_raw_dev_data_t *rawdevice = mtd->priv;
  size_t from;
  u_long len;
  int err = 0;

  /* check readonly */
  if(rawdevice->readonly) {
    printk("blkmtd: error: trying to erase readonly device %s\n", device);
    instr->state = MTD_ERASE_FAILED;
    goto erase_callback;
  }

  instr->state = MTD_ERASING;
  from = instr->addr;
  len = instr->len;

  /* check page alignment of start and length */
  DEBUG(2, "blkmtd: erase: dev = `%s' from = %d len = %ld\n",
	bdevname(rawdevice->binding->bd_dev), from, len);
  if(from % PAGE_SIZE) {
    printk("blkmtd: erase: addr not page aligned (addr = %d)\n", from);
    instr->state = MTD_ERASE_FAILED;
    err = -EIO;
  }

  if(len % PAGE_SIZE) {
    printk("blkmtd: erase: len not a whole number of pages (len = %ld)\n", len);
    instr->state = MTD_ERASE_FAILED;
    err = -EIO;
  }
  
  if(instr->state != MTD_ERASE_FAILED) {
    /* start the erase */
    int pagenr, pagecnt;
    struct page *page, **pages;
    int i = 0;

    pagenr = from >> PAGE_SHIFT;
    pagecnt = len >> PAGE_SHIFT;
    DEBUG(3, "blkmtd: erase: pagenr = %d pagecnt = %d\n", pagenr, pagecnt);
    pages = kmalloc(pagecnt * sizeof(struct page *), GFP_KERNEL);
    if(pages == NULL) {
      err = -ENOMEM;
      instr->state = MTD_ERASE_FAILED;
      goto erase_out;
    }

    while(pagecnt) {
      /* get the page via the page cache */
      DEBUG(3, "blkmtd: erase: doing grap_cache_page() for page %d\n", pagenr);
      page = grab_cache_page(&rawdevice->as, pagenr);
      if(!page) {
	DEBUG(3, "blkmtd: erase: grab_cache_page() failed for page %d\n", pagenr);
	kfree(pages);
	err = -EIO;
	instr->state = MTD_ERASE_FAILED;
	goto erase_out;
      }
      memset(page_address(page), 0xff, PAGE_SIZE);
      pages[i] = page;
      pagecnt--;
      pagenr++;
      i++;
    }
    DEBUG(3, "blkmtd: erase: queuing page write\n");
    err = queue_page_write(rawdevice, pages, from >> PAGE_SHIFT, len >> PAGE_SHIFT, 1);
    pagecnt = len >> PAGE_SHIFT;
    if(!err) {
      while(pagecnt--) {
	SetPageUptodate(pages[pagecnt]);
	UnlockPage(pages[pagecnt]);
	page_cache_release(pages[pagecnt]);
	flush_dcache_page(pages[pagecnt]);
      }