/*
   * fs/fs-writeback.c
   *
   * Copyright (C) 2002, Linus Torvalds.
   *
   * Contains all the functions related to writing back and waiting
   * upon dirty inodes against superblocks, and writing back dirty
   * pages against inodes.  ie: data writeback.  Writeout of the
   * inode itself is not handled here.
   *
   * 10Apr2002	akpm@zip.com.au
   *		Split out of fs/inode.c
   *		Additions for address_space-based writeback
   */
  
  #include <linux/kernel.h>
  #include <linux/spinlock.h>
  #include <linux/sched.h>
  #include <linux/fs.h>
  #include <linux/mm.h>
  #include <linux/writeback.h>
  #include <linux/blkdev.h>
  #include <linux/backing-dev.h>
  #include <linux/buffer_head.h>

  #include "internal.h"

  
  /**
   *	__mark_inode_dirty -	internal function
   *	@inode: inode to mark
   *	@flags: what kind of dirty (i.e. I_DIRTY_SYNC)
   *	Mark an inode as dirty. Callers should use mark_inode_dirty or
   *  	mark_inode_dirty_sync.
   *
   * Put the inode on the super block's dirty list.
   *
   * CAREFUL! We mark it dirty unconditionally, but move it onto the
   * dirty list only if it is hashed or if it refers to a blockdev.
   * If it was not hashed, it will never be added to the dirty list
   * even if it is later hashed, as it will have been marked dirty already.
   *
   * In short, make sure you hash any inodes _before_ you start marking
   * them dirty.
   *
   * This function *must* be atomic for the I_DIRTY_PAGES case -
   * set_page_dirty() is called under spinlock in several places.
   *
   * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
   * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
   * the kernel-internal blockdev inode represents the dirtying time of the
   * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
   * page->mapping->host, so the page-dirtying time is recorded in the internal
   * blockdev inode.
   */
  void __mark_inode_dirty(struct inode *inode, int flags)
  {
  	struct super_block *sb = inode->i_sb;
  
  	/*
  	 * Don't do this for I_DIRTY_PAGES - that doesn't actually
  	 * dirty the inode itself
  	 */
  	if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
  		if (sb->s_op->dirty_inode)
  			sb->s_op->dirty_inode(inode);
  	}
  
  	/*
  	 * make sure that changes are seen by all cpus before we test i_state
  	 * -- mikulas
  	 */
  	smp_mb();
  
  	/* avoid the locking if we can */
  	if ((inode->i_state & flags) == flags)
  		return;
  
  	if (unlikely(block_dump)) {
  		struct dentry *dentry = NULL;
  		const char *name = "?";
  
  		if (!list_empty(&inode->i_dentry)) {
  			dentry = list_entry(inode->i_dentry.next,
  					    struct dentry, d_alias);
  			if (dentry && dentry->d_name.name)
  				name = (const char *) dentry->d_name.name;
  		}
  
  		if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev"))
  			printk(KERN_DEBUG
  			       "%s(%d): dirtied inode %lu (%s) on %s
  ",
  			       current->comm, current->pid, inode->i_ino,
  			       name, inode->i_sb->s_id);
  	}
  
  	spin_lock(&inode_lock);
  	if ((inode->i_state & flags) != flags) {
  		const int was_dirty = inode->i_state & I_DIRTY;
  
  		inode->i_state |= flags;
  
  		/*
  		 * If the inode is locked, just update its dirty state. 
  		 * The unlocker will place the inode on the appropriate
  		 * superblock list, based upon its state.
  		 */
  		if (inode->i_state & I_LOCK)
  			goto out;
  
  		/*
  		 * Only add valid (hashed) inodes to the superblock's
  		 * dirty list.  Add blockdev inodes as well.
  		 */
  		if (!S_ISBLK(inode->i_mode)) {
  			if (hlist_unhashed(&inode->i_hash))
  				goto out;
  		}
  		if (inode->i_state & (I_FREEING|I_CLEAR))
  			goto out;
  
  		/*
  		 * If the inode was already on s_dirty or s_io, don't
  		 * reposition it (that would break s_dirty time-ordering).
  		 */
  		if (!was_dirty) {
  			inode->dirtied_when = jiffies;
  			list_move(&inode->i_list, &sb->s_dirty);
  		}
  	}
  out:
  	spin_unlock(&inode_lock);
  }
  
  EXPORT_SYMBOL(__mark_inode_dirty);
  
  static int write_inode(struct inode *inode, int sync)
  {
  	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
  		return inode->i_sb->s_op->write_inode(inode, sync);
  	return 0;
  }
  
  /*
   * Write a single inode's dirty pages and inode data out to disk.
   * If `wait' is set, wait on the writeout.
   *
   * The whole writeout design is quite complex and fragile.  We want to avoid
   * starvation of particular inodes when others are being redirtied, prevent
   * livelocks, etc.
   *
   * Called under inode_lock.
   */
  static int
  __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
  {
  	unsigned dirty;
  	struct address_space *mapping = inode->i_mapping;
  	struct super_block *sb = inode->i_sb;
  	int wait = wbc->sync_mode == WB_SYNC_ALL;
  	int ret;
  
  	BUG_ON(inode->i_state & I_LOCK);
  
  	/* Set I_LOCK, reset I_DIRTY */
  	dirty = inode->i_state & I_DIRTY;
  	inode->i_state |= I_LOCK;
  	inode->i_state &= ~I_DIRTY;
  
  	spin_unlock(&inode_lock);
  
  	ret = do_writepages(mapping, wbc);
  
  	/* Don't write the inode if only I_DIRTY_PAGES was set */
  	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
  		int err = write_inode(inode, wait);
  		if (ret == 0)
  			ret = err;
  	}
  
  	if (wait) {
  		int err = filemap_fdatawait(mapping);
  		if (ret == 0)
  			ret = err;
  	}
  
  	spin_lock(&inode_lock);
  	inode->i_state &= ~I_LOCK;
  	if (!(inode->i_state & I_FREEING)) {
  		if (!(inode->i_state & I_DIRTY) &&
  		    mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
  			/*
  			 * We didn't write back all the pages.  nfs_writepages()
  			 * sometimes bales out without doing anything. Redirty
  			 * the inode.  It is still on sb->s_io.
  			 */
  			if (wbc->for_kupdate) {
  				/*
  				 * For the kupdate function we leave the inode
  				 * at the head of sb_dirty so it will get more
  				 * writeout as soon as the queue becomes
  				 * uncongested.
  				 */
  				inode->i_state |= I_DIRTY_PAGES;
  				list_move_tail(&inode->i_list, &sb->s_dirty);
  			} else {
  				/*
  				 * Otherwise fully redirty the inode so that
  				 * other inodes on this superblock will get some
  				 * writeout.  Otherwise heavy writing to one
  				 * file would indefinitely suspend writeout of
  				 * all the other files.
  				 */
  				inode->i_state |= I_DIRTY_PAGES;
  				inode->dirtied_when = jiffies;
  				list_move(&inode->i_list, &sb->s_dirty);
  			}
  		} else if (inode->i_state & I_DIRTY) {
  			/*
  			 * Someone redirtied the inode while were writing back
  			 * the pages.
  			 */
  			list_move(&inode->i_list, &sb->s_dirty);
  		} else if (atomic_read(&inode->i_count)) {
  			/*
  			 * The inode is clean, inuse
  			 */
  			list_move(&inode->i_list, &inode_in_use);
  		} else {
  			/*
  			 * The inode is clean, unused
  			 */
  			list_move(&inode->i_list, &inode_unused);

  		}
  	}
  	wake_up_inode(inode);
  	return ret;
  }
  
  /*

   * Write out an inode's dirty pages.  Called under inode_lock.  Either the
   * caller has ref on the inode (either via __iget or via syscall against an fd)
   * or the inode has I_WILL_FREE set (via generic_forget_inode)

   */
  static int

  __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)

  {
  	wait_queue_head_t *wqh;

  	if (!atomic_read(&inode->i_count))

  		WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));

  	else
  		WARN_ON(inode->i_state & I_WILL_FREE);

  	if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_LOCK)) {

  		struct address_space *mapping = inode->i_mapping;
  		int ret;

  		list_move(&inode->i_list, &inode->i_sb->s_dirty);

  
  		/*
  		 * Even if we don't actually write the inode itself here,
  		 * we can at least start some of the data writeout..
  		 */
  		spin_unlock(&inode_lock);
  		ret = do_writepages(mapping, wbc);
  		spin_lock(&inode_lock);
  		return ret;

  	}
  
  	/*
  	 * It's a data-integrity sync.  We must wait.
  	 */
  	if (inode->i_state & I_LOCK) {
  		DEFINE_WAIT_BIT(wq, &inode->i_state, __I_LOCK);
  
  		wqh = bit_waitqueue(&inode->i_state, __I_LOCK);
  		do {

  			spin_unlock(&inode_lock);
  			__wait_on_bit(wqh, &wq, inode_wait,
  							TASK_UNINTERRUPTIBLE);

  			spin_lock(&inode_lock);
  		} while (inode->i_state & I_LOCK);
  	}
  	return __sync_single_inode(inode, wbc);
  }
  
  /*
   * Write out a superblock's list of dirty inodes.  A wait will be performed
   * upon no inodes, all inodes or the final one, depending upon sync_mode.
   *
   * If older_than_this is non-NULL, then only write out inodes which
   * had their first dirtying at a time earlier than *older_than_this.
   *
   * If we're a pdlfush thread, then implement pdflush collision avoidance
   * against the entire list.
   *
   * WB_SYNC_HOLD is a hack for sys_sync(): reattach the inode to sb->s_dirty so
   * that it can be located for waiting on in __writeback_single_inode().
   *
   * Called under inode_lock.
   *
   * If `bdi' is non-zero then we're being asked to writeback a specific queue.
   * This function assumes that the blockdev superblock's inodes are backed by
   * a variety of queues, so all inodes are searched.  For other superblocks,
   * assume that all inodes are backed by the same queue.
   *
   * FIXME: this linear search could get expensive with many fileystems.  But
   * how to fix?  We need to go from an address_space to all inodes which share
   * a queue with that address_space.  (Easy: have a global "dirty superblocks"
   * list).
   *
   * The inodes to be written are parked on sb->s_io.  They are moved back onto
   * sb->s_dirty as they are selected for writing.  This way, none can be missed
   * on the writer throttling path, and we get decent balancing between many
   * throttled threads: we don't want them all piling up on __wait_on_inode.
   */
  static void
  sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
  {
  	const unsigned long start = jiffies;	/* livelock avoidance */
  
  	if (!wbc->for_kupdate || list_empty(&sb->s_io))
  		list_splice_init(&sb->s_dirty, &sb->s_io);
  
  	while (!list_empty(&sb->s_io)) {
  		struct inode *inode = list_entry(sb->s_io.prev,
  						struct inode, i_list);
  		struct address_space *mapping = inode->i_mapping;
  		struct backing_dev_info *bdi = mapping->backing_dev_info;
  		long pages_skipped;
  
  		if (!bdi_cap_writeback_dirty(bdi)) {
  			list_move(&inode->i_list, &sb->s_dirty);

  			if (sb_is_blkdev_sb(sb)) {

  				/*
  				 * Dirty memory-backed blockdev: the ramdisk
  				 * driver does this.  Skip just this inode
  				 */
  				continue;
  			}
  			/*
  			 * Dirty memory-backed inode against a filesystem other
  			 * than the kernel-internal bdev filesystem.  Skip the
  			 * entire superblock.
  			 */
  			break;
  		}
  
  		if (wbc->nonblocking && bdi_write_congested(bdi)) {
  			wbc->encountered_congestion = 1;

  			if (!sb_is_blkdev_sb(sb))

  				break;		/* Skip a congested fs */
  			list_move(&inode->i_list, &sb->s_dirty);
  			continue;		/* Skip a congested blockdev */
  		}
  
  		if (wbc->bdi && bdi != wbc->bdi) {

  			if (!sb_is_blkdev_sb(sb))

  				break;		/* fs has the wrong queue */
  			list_move(&inode->i_list, &sb->s_dirty);
  			continue;		/* blockdev has wrong queue */
  		}
  
  		/* Was this inode dirtied after sync_sb_inodes was called? */
  		if (time_after(inode->dirtied_when, start))
  			break;
  
  		/* Was this inode dirtied too recently? */
  		if (wbc->older_than_this && time_after(inode->dirtied_when,
  						*wbc->older_than_this))
  			break;
  
  		/* Is another pdflush already flushing this queue? */
  		if (current_is_pdflush() && !writeback_acquire(bdi))
  			break;
  
  		BUG_ON(inode->i_state & I_FREEING);
  		__iget(inode);
  		pages_skipped = wbc->pages_skipped;
  		__writeback_single_inode(inode, wbc);
  		if (wbc->sync_mode == WB_SYNC_HOLD) {
  			inode->dirtied_when = jiffies;
  			list_move(&inode->i_list, &sb->s_dirty);
  		}
  		if (current_is_pdflush())
  			writeback_release(bdi);
  		if (wbc->pages_skipped != pages_skipped) {
  			/*
  			 * writeback is not making progress due to locked
  			 * buffers.  Skip this inode for now.
  			 */
  			list_move(&inode->i_list, &sb->s_dirty);
  		}
  		spin_unlock(&inode_lock);

  		iput(inode);

  		cond_resched();

  		spin_lock(&inode_lock);
  		if (wbc->nr_to_write <= 0)
  			break;
  	}
  	return;		/* Leave any unwritten inodes on s_io */
  }
  
  /*
   * Start writeback of dirty pagecache data against all unlocked inodes.
   *
   * Note:
   * We don't need to grab a reference to superblock here. If it has non-empty
   * ->s_dirty it's hadn't been killed yet and kill_super() won't proceed
   * past sync_inodes_sb() until both the ->s_dirty and ->s_io lists are
   * empty. Since __sync_single_inode() regains inode_lock before it finally moves
   * inode from superblock lists we are OK.
   *
   * If `older_than_this' is non-zero then only flush inodes which have a
   * flushtime older than *older_than_this.
   *
   * If `bdi' is non-zero then we will scan the first inode against each
   * superblock until we find the matching ones.  One group will be the dirty
   * inodes against a filesystem.  Then when we hit the dummy blockdev superblock,
   * sync_sb_inodes will seekout the blockdev which matches `bdi'.  Maybe not
   * super-efficient but we're about to do a ton of I/O...
   */
  void
  writeback_inodes(struct writeback_control *wbc)
  {
  	struct super_block *sb;
  
  	might_sleep();
  	spin_lock(&sb_lock);
  restart:
  	sb = sb_entry(super_blocks.prev);
  	for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) {
  		if (!list_empty(&sb->s_dirty) || !list_empty(&sb->s_io)) {
  			/* we're making our own get_super here */
  			sb->s_count++;
  			spin_unlock(&sb_lock);
  			/*
  			 * If we can't get the readlock, there's no sense in
  			 * waiting around, most of the time the FS is going to
  			 * be unmounted by the time it is released.
  			 */
  			if (down_read_trylock(&sb->s_umount)) {
  				if (sb->s_root) {
  					spin_lock(&inode_lock);
  					sync_sb_inodes(sb, wbc);
  					spin_unlock(&inode_lock);
  				}
  				up_read(&sb->s_umount);
  			}
  			spin_lock(&sb_lock);
  			if (__put_super_and_need_restart(sb))
  				goto restart;
  		}
  		if (wbc->nr_to_write <= 0)
  			break;
  	}
  	spin_unlock(&sb_lock);
  }
  
  /*
   * writeback and wait upon the filesystem's dirty inodes.  The caller will
   * do this in two passes - one to write, and one to wait.  WB_SYNC_HOLD is
   * used to park the written inodes on sb->s_dirty for the wait pass.
   *
   * A finite limit is set on the number of pages which will be written.
   * To prevent infinite livelock of sys_sync().
   *
   * We add in the number of potentially dirty inodes, because each inode write
   * can dirty pagecache in the underlying blockdev.
   */
  void sync_inodes_sb(struct super_block *sb, int wait)
  {
  	struct writeback_control wbc = {
  		.sync_mode	= wait ? WB_SYNC_ALL : WB_SYNC_HOLD,

  		.range_start	= 0,
  		.range_end	= LLONG_MAX,

  	};

  	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);

  	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);

  
  	wbc.nr_to_write = nr_dirty + nr_unstable +
  			(inodes_stat.nr_inodes - inodes_stat.nr_unused) +
  			nr_dirty + nr_unstable;
  	wbc.nr_to_write += wbc.nr_to_write / 2;		/* Bit more for luck */
  	spin_lock(&inode_lock);
  	sync_sb_inodes(sb, &wbc);
  	spin_unlock(&inode_lock);
  }
  
  /*
   * Rather lame livelock avoidance.
   */
  static void set_sb_syncing(int val)
  {
  	struct super_block *sb;
  	spin_lock(&sb_lock);
  	sb = sb_entry(super_blocks.prev);
  	for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) {
  		sb->s_syncing = val;
  	}
  	spin_unlock(&sb_lock);
  }

  /**

   * sync_inodes - writes all inodes to disk
   * @wait: wait for completion

   *
   * sync_inodes() goes through each super block's dirty inode list, writes the
   * inodes out, waits on the writeout and puts the inodes back on the normal
   * list.
   *
   * This is for sys_sync().  fsync_dev() uses the same algorithm.  The subtle
   * part of the sync functions is that the blockdev "superblock" is processed
   * last.  This is because the write_inode() function of a typical fs will
   * perform no I/O, but will mark buffers in the blockdev mapping as dirty.
   * What we want to do is to perform all that dirtying first, and then write
   * back all those inode blocks via the blockdev mapping in one sweep.  So the
   * additional (somewhat redundant) sync_blockdev() calls here are to make
   * sure that really happens.  Because if we call sync_inodes_sb(wait=1) with
   * outstanding dirty inodes, the writeback goes block-at-a-time within the
   * filesystem's write_inode().  This is extremely slow.
   */

  static void __sync_inodes(int wait)

  {
  	struct super_block *sb;

  	spin_lock(&sb_lock);
  restart:
  	list_for_each_entry(sb, &super_blocks, s_list) {
  		if (sb->s_syncing)
  			continue;
  		sb->s_syncing = 1;
  		sb->s_count++;
  		spin_unlock(&sb_lock);
  		down_read(&sb->s_umount);
  		if (sb->s_root) {
  			sync_inodes_sb(sb, wait);
  			sync_blockdev(sb->s_bdev);
  		}
  		up_read(&sb->s_umount);
  		spin_lock(&sb_lock);
  		if (__put_super_and_need_restart(sb))
  			goto restart;

  	}

  	spin_unlock(&sb_lock);
  }
  
  void sync_inodes(int wait)
  {
  	set_sb_syncing(0);
  	__sync_inodes(0);

  	if (wait) {
  		set_sb_syncing(0);

  		__sync_inodes(1);

  	}
  }
  
  /**

   * write_inode_now	-	write an inode to disk
   * @inode: inode to write to disk
   * @sync: whether the write should be synchronous or not
   *
   * This function commits an inode to disk immediately if it is dirty. This is
   * primarily needed by knfsd.

   *

   * The caller must either have a ref on the inode or must have set I_WILL_FREE.

   */

  int write_inode_now(struct inode *inode, int sync)
  {
  	int ret;
  	struct writeback_control wbc = {
  		.nr_to_write = LONG_MAX,
  		.sync_mode = WB_SYNC_ALL,

  		.range_start = 0,
  		.range_end = LLONG_MAX,

  	};
  
  	if (!mapping_cap_writeback_dirty(inode->i_mapping))

  		wbc.nr_to_write = 0;

  
  	might_sleep();
  	spin_lock(&inode_lock);
  	ret = __writeback_single_inode(inode, &wbc);
  	spin_unlock(&inode_lock);
  	if (sync)
  		wait_on_inode(inode);
  	return ret;
  }
  EXPORT_SYMBOL(write_inode_now);
  
  /**
   * sync_inode - write an inode and its pages to disk.
   * @inode: the inode to sync
   * @wbc: controls the writeback mode
   *
   * sync_inode() will write an inode and its pages to disk.  It will also
   * correctly update the inode on its superblock's dirty inode lists and will
   * update inode->i_state.
   *
   * The caller must have a ref on the inode.
   */
  int sync_inode(struct inode *inode, struct writeback_control *wbc)
  {
  	int ret;
  
  	spin_lock(&inode_lock);
  	ret = __writeback_single_inode(inode, wbc);
  	spin_unlock(&inode_lock);
  	return ret;
  }
  EXPORT_SYMBOL(sync_inode);
  
  /**
   * generic_osync_inode - flush all dirty data for a given inode to disk
   * @inode: inode to write

   * @mapping: the address_space that should be flushed

   * @what:  what to write and wait upon
   *
   * This can be called by file_write functions for files which have the
   * O_SYNC flag set, to flush dirty writes to disk.
   *
   * @what is a bitmask, specifying which part of the inode's data should be

   * written and waited upon.

   *
   *    OSYNC_DATA:     i_mapping's dirty data
   *    OSYNC_METADATA: the buffers at i_mapping->private_list
   *    OSYNC_INODE:    the inode itself
   */
  
  int generic_osync_inode(struct inode *inode, struct address_space *mapping, int what)
  {
  	int err = 0;
  	int need_write_inode_now = 0;
  	int err2;

  	if (what & OSYNC_DATA)
  		err = filemap_fdatawrite(mapping);
  	if (what & (OSYNC_METADATA|OSYNC_DATA)) {
  		err2 = sync_mapping_buffers(mapping);
  		if (!err)
  			err = err2;
  	}
  	if (what & OSYNC_DATA) {
  		err2 = filemap_fdatawait(mapping);
  		if (!err)
  			err = err2;
  	}

  
  	spin_lock(&inode_lock);
  	if ((inode->i_state & I_DIRTY) &&
  	    ((what & OSYNC_INODE) || (inode->i_state & I_DIRTY_DATASYNC)))
  		need_write_inode_now = 1;
  	spin_unlock(&inode_lock);
  
  	if (need_write_inode_now) {
  		err2 = write_inode_now(inode, 1);
  		if (!err)
  			err = err2;
  	}
  	else
  		wait_on_inode(inode);
  
  	return err;
  }
  
  EXPORT_SYMBOL(generic_osync_inode);
  
  /**
   * writeback_acquire: attempt to get exclusive writeback access to a device
   * @bdi: the device's backing_dev_info structure
   *
   * It is a waste of resources to have more than one pdflush thread blocked on
   * a single request queue.  Exclusion at the request_queue level is obtained
   * via a flag in the request_queue's backing_dev_info.state.
   *
   * Non-request_queue-backed address_spaces will share default_backing_dev_info,
   * unless they implement their own.  Which is somewhat inefficient, as this
   * may prevent concurrent writeback against multiple devices.
   */
  int writeback_acquire(struct backing_dev_info *bdi)
  {
  	return !test_and_set_bit(BDI_pdflush, &bdi->state);
  }
  
  /**
   * writeback_in_progress: determine whether there is writeback in progress

   * @bdi: the device's backing_dev_info structure.

   *
   * Determine whether there is writeback in progress against a backing device.

   */
  int writeback_in_progress(struct backing_dev_info *bdi)
  {
  	return test_bit(BDI_pdflush, &bdi->state);
  }
  
  /**
   * writeback_release: relinquish exclusive writeback access against a device.
   * @bdi: the device's backing_dev_info structure
   */
  void writeback_release(struct backing_dev_info *bdi)
  {
  	BUG_ON(!writeback_in_progress(bdi));
  	clear_bit(BDI_pdflush, &bdi->state);
  }