Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 695 insertions, 0 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
new file mode 100644
index 000000000000..d6efb36cab2a
--- /dev/null
+++ b/fs/fs-writeback.c
@@ -0,0 +1,695 @@
+/*
+ * 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>
+
+extern struct super_block *blockdev_superblock;
+
+/**
+ *      __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\n",
+                               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);
+                        inodes_stat.nr_unused++;
+                }
+        }
+        wake_up_inode(inode);
+        return ret;
+}
+
+/*
+ * Write out an inode's dirty pages.  Called under inode_lock.
+ */
+static int
+__writeback_single_inode(struct inode *inode,
+                        struct writeback_control *wbc)
+{
+        wait_queue_head_t *wqh;
+
+        if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_LOCK)) {
+                list_move(&inode->i_list, &inode->i_sb->s_dirty);
+                return 0;
+        }
+
+        /*
+         * 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 {
+                        __iget(inode);
+                        spin_unlock(&inode_lock);
+                        __wait_on_bit(wqh, &wq, inode_wait,
+                                                        TASK_UNINTERRUPTIBLE);
+                        iput(inode);
+                        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 == blockdev_superblock) {
+                                /*
+                                 * 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 != blockdev_superblock)
+                                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 != blockdev_superblock)
+                                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);
+                cond_resched();
+                iput(inode);
+                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,
+        };
+        unsigned long nr_dirty = read_page_state(nr_dirty);
+        unsigned long nr_unstable = read_page_state(nr_unstable);
+
+        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);
+}
+
+/*
+ * Find a superblock with inodes that need to be synced
+ */
+static struct super_block *get_super_to_sync(void)
+{
+        struct super_block *sb;
+restart:
+        spin_lock(&sb_lock);
+        sb = sb_entry(super_blocks.prev);
+        for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) {
+                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) {
+                        drop_super(sb);
+                        goto restart;
+                }
+                return sb;
+        }
+        spin_unlock(&sb_lock);
+        return NULL;
+}
+
+/**
+ * sync_inodes
+ *
+ * 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.
+ */
+void sync_inodes(int wait)
+{
+        struct super_block *sb;
+
+        set_sb_syncing(0);
+        while ((sb = get_super_to_sync()) != NULL) {
+                sync_inodes_sb(sb, 0);
+                sync_blockdev(sb->s_bdev);
+                drop_super(sb);
+        }
+        if (wait) {
+                set_sb_syncing(0);
+                while ((sb = get_super_to_sync()) != NULL) {
+                        sync_inodes_sb(sb, 1);
+                        sync_blockdev(sb->s_bdev);
+                        drop_super(sb);
+                }
+        }
+}
+
+/**
+ *      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.
+ */
+ 
+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,
+        };
+
+        if (!mapping_cap_writeback_dirty(inode->i_mapping))
+                return 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
+ * @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;
+
+        current->flags |= PF_SYNCWRITE;
+        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;
+        }
+        current->flags &= ~PF_SYNCWRITE;
+
+        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
+ *                        against a backing device.
+ * @bdi: the device's backing_dev_info structure.
+ */
+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);
+}