1 files changed, 835 insertions, 0 deletions

diff --git a/fs/afs/write.c b/fs/afs/write.c
new file mode 100644
index 00000000000..83ff2926281
--- /dev/null
+++ b/fs/afs/write.c
@@ -0,0 +1,835 @@
+/* handling of writes to regular files and writing back to the server
+ *
+ * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include <linux/writeback.h>
+#include <linux/pagevec.h>
+#include "internal.h"
+
+static int afs_write_back_from_locked_page(struct afs_writeback *wb,
+					   struct page *page);
+
+/*
+ * mark a page as having been made dirty and thus needing writeback
+ */
+int afs_set_page_dirty(struct page *page)
+{
+	_enter("");
+	return __set_page_dirty_nobuffers(page);
+}
+
+/*
+ * unlink a writeback record because its usage has reached zero
+ * - must be called with the wb->vnode->writeback_lock held
+ */
+static void afs_unlink_writeback(struct afs_writeback *wb)
+{
+	struct afs_writeback *front;
+	struct afs_vnode *vnode = wb->vnode;
+
+	list_del_init(&wb->link);
+	if (!list_empty(&vnode->writebacks)) {
+		/* if an fsync rises to the front of the queue then wake it
+		 * up */
+		front = list_entry(vnode->writebacks.next,
+				   struct afs_writeback, link);
+		if (front->state == AFS_WBACK_SYNCING) {
+			_debug("wake up sync");
+			front->state = AFS_WBACK_COMPLETE;
+			wake_up(&front->waitq);
+		}
+	}
+}
+
+/*
+ * free a writeback record
+ */
+static void afs_free_writeback(struct afs_writeback *wb)
+{
+	_enter("");
+	key_put(wb->key);
+	kfree(wb);
+}
+
+/*
+ * dispose of a reference to a writeback record
+ */
+void afs_put_writeback(struct afs_writeback *wb)
+{
+	struct afs_vnode *vnode = wb->vnode;
+
+	_enter("{%d}", wb->usage);
+
+	spin_lock(&vnode->writeback_lock);
+	if (--wb->usage == 0)
+		afs_unlink_writeback(wb);
+	else
+		wb = NULL;
+	spin_unlock(&vnode->writeback_lock);
+	if (wb)
+		afs_free_writeback(wb);
+}
+
+/*
+ * partly or wholly fill a page that's under preparation for writing
+ */
+static int afs_fill_page(struct afs_vnode *vnode, struct key *key,
+			 unsigned start, unsigned len, struct page *page)
+{
+	int ret;
+
+	_enter(",,%u,%u", start, len);
+
+	ASSERTCMP(start + len, <=, PAGE_SIZE);
+
+	ret = afs_vnode_fetch_data(vnode, key, start, len, page);
+	if (ret < 0) {
+		if (ret == -ENOENT) {
+			_debug("got NOENT from server"
+			       " - marking file deleted and stale");
+			set_bit(AFS_VNODE_DELETED, &vnode->flags);
+			ret = -ESTALE;
+		}
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * prepare a page for being written to
+ */
+static int afs_prepare_page(struct afs_vnode *vnode, struct page *page,
+			    struct key *key, unsigned offset, unsigned to)
+{
+	unsigned eof, tail, start, stop, len;
+	loff_t i_size, pos;
+	void *p;
+	int ret;
+
+	_enter("");
+
+	if (offset == 0 && to == PAGE_SIZE)
+		return 0;
+
+	p = kmap(page);
+
+	i_size = i_size_read(&vnode->vfs_inode);
+	pos = (loff_t) page->index << PAGE_SHIFT;
+	if (pos >= i_size) {
+		/* partial write, page beyond EOF */
+		_debug("beyond");
+		if (offset > 0)
+			memset(p, 0, offset);
+		if (to < PAGE_SIZE)
+			memset(p + to, 0, PAGE_SIZE - to);
+		kunmap(page);
+		return 0;
+	}
+
+	if (i_size - pos >= PAGE_SIZE) {
+		/* partial write, page entirely before EOF */
+		_debug("before");
+		tail = eof = PAGE_SIZE;
+	} else {
+		/* partial write, page overlaps EOF */
+		eof = i_size - pos;
+		_debug("overlap %u", eof);
+		tail = max(eof, to);
+		if (tail < PAGE_SIZE)
+			memset(p + tail, 0, PAGE_SIZE - tail);
+		if (offset > eof)
+			memset(p + eof, 0, PAGE_SIZE - eof);
+	}
+
+	kunmap(p);
+
+	ret = 0;
+	if (offset > 0 || eof > to) {
+		/* need to fill one or two bits that aren't going to be written
+		 * (cover both fillers in one read if there are two) */
+		start = (offset > 0) ? 0 : to;
+		stop = (eof > to) ? eof : offset;
+		len = stop - start;
+		_debug("wr=%u-%u av=0-%u rd=%u@%u",
+		       offset, to, eof, start, len);
+		ret = afs_fill_page(vnode, key, start, len, page);
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * prepare to perform part of a write to a page
+ * - the caller holds the page locked, preventing it from being written out or
+ *   modified by anyone else
+ */
+int afs_prepare_write(struct file *file, struct page *page,
+		      unsigned offset, unsigned to)
+{
+	struct afs_writeback *candidate, *wb;
+	struct afs_vnode *vnode = AFS_FS_I(file->f_dentry->d_inode);
+	struct key *key = file->private_data;
+	pgoff_t index;
+	int ret;
+
+	_enter("{%x:%u},{%lx},%u,%u",
+	       vnode->fid.vid, vnode->fid.vnode, page->index, offset, to);
+
+	candidate = kzalloc(sizeof(*candidate), GFP_KERNEL);
+	if (!candidate)
+		return -ENOMEM;
+	candidate->vnode = vnode;
+	candidate->first = candidate->last = page->index;
+	candidate->offset_first = offset;
+	candidate->to_last = to;
+	candidate->usage = 1;
+	candidate->state = AFS_WBACK_PENDING;
+	init_waitqueue_head(&candidate->waitq);
+
+	if (!PageUptodate(page)) {
+		_debug("not up to date");
+		ret = afs_prepare_page(vnode, page, key, offset, to);
+		if (ret < 0) {
+			kfree(candidate);
+			_leave(" = %d [prep]", ret);
+			return ret;
+		}
+		SetPageUptodate(page);
+	}
+
+try_again:
+	index = page->index;
+	spin_lock(&vnode->writeback_lock);
+
+	/* see if this page is already pending a writeback under a suitable key
+	 * - if so we can just join onto that one */
+	wb = (struct afs_writeback *) page_private(page);
+	if (wb) {
+		if (wb->key == key && wb->state == AFS_WBACK_PENDING)
+			goto subsume_in_current_wb;
+		goto flush_conflicting_wb;
+	}
+
+	if (index > 0) {
+		/* see if we can find an already pending writeback that we can
+		 * append this page to */
+		list_for_each_entry(wb, &vnode->writebacks, link) {
+			if (wb->last == index - 1 && wb->key == key &&
+			    wb->state == AFS_WBACK_PENDING)
+				goto append_to_previous_wb;
+		}
+	}
+
+	list_add_tail(&candidate->link, &vnode->writebacks);
+	candidate->key = key_get(key);
+	spin_unlock(&vnode->writeback_lock);
+	SetPagePrivate(page);
+	set_page_private(page, (unsigned long) candidate);
+	_leave(" = 0 [new]");
+	return 0;
+
+subsume_in_current_wb:
+	_debug("subsume");
+	ASSERTRANGE(wb->first, <=, index, <=, wb->last);
+	if (index == wb->first && offset < wb->offset_first)
+		wb->offset_first = offset;
+	if (index == wb->last && to > wb->to_last)
+		wb->to_last = to;
+	spin_unlock(&vnode->writeback_lock);
+	kfree(candidate);
+	_leave(" = 0 [sub]");
+	return 0;
+
+append_to_previous_wb:
+	_debug("append into %lx-%lx", wb->first, wb->last);
+	wb->usage++;
+	wb->last++;
+	wb->to_last = to;
+	spin_unlock(&vnode->writeback_lock);
+	SetPagePrivate(page);
+	set_page_private(page, (unsigned long) wb);
+	kfree(candidate);
+	_leave(" = 0 [app]");
+	return 0;
+
+	/* the page is currently bound to another context, so if it's dirty we
+	 * need to flush it before we can use the new context */
+flush_conflicting_wb:
+	_debug("flush conflict");
+	if (wb->state == AFS_WBACK_PENDING)
+		wb->state = AFS_WBACK_CONFLICTING;
+	spin_unlock(&vnode->writeback_lock);
+	if (PageDirty(page)) {
+		ret = afs_write_back_from_locked_page(wb, page);
+		if (ret < 0) {
+			afs_put_writeback(candidate);
+			_leave(" = %d", ret);
+			return ret;
+		}
+	}
+
+	/* the page holds a ref on the writeback record */
+	afs_put_writeback(wb);
+	set_page_private(page, 0);
+	ClearPagePrivate(page);
+	goto try_again;
+}
+
+/*
+ * finalise part of a write to a page
+ */
+int afs_commit_write(struct file *file, struct page *page,
+		     unsigned offset, unsigned to)
+{
+	struct afs_vnode *vnode = AFS_FS_I(file->f_dentry->d_inode);
+	loff_t i_size, maybe_i_size;
+
+	_enter("{%x:%u},{%lx},%u,%u",
+	       vnode->fid.vid, vnode->fid.vnode, page->index, offset, to);
+
+	maybe_i_size = (loff_t) page->index << PAGE_SHIFT;
+	maybe_i_size += to;
+
+	i_size = i_size_read(&vnode->vfs_inode);
+	if (maybe_i_size > i_size) {
+		spin_lock(&vnode->writeback_lock);
+		i_size = i_size_read(&vnode->vfs_inode);
+		if (maybe_i_size > i_size)
+			i_size_write(&vnode->vfs_inode, maybe_i_size);
+		spin_unlock(&vnode->writeback_lock);
+	}
+
+	set_page_dirty(page);
+
+	if (PageDirty(page))
+		_debug("dirtied");
+
+	return 0;
+}
+
+/*
+ * kill all the pages in the given range
+ */
+static void afs_kill_pages(struct afs_vnode *vnode, bool error,
+			   pgoff_t first, pgoff_t last)
+{
+	struct pagevec pv;
+	unsigned count, loop;
+
+	_enter("{%x:%u},%lx-%lx",
+	       vnode->fid.vid, vnode->fid.vnode, first, last);
+
+	pagevec_init(&pv, 0);
+
+	do {
+		_debug("kill %lx-%lx", first, last);
+
+		count = last - first + 1;
+		if (count > PAGEVEC_SIZE)
+			count = PAGEVEC_SIZE;
+		pv.nr = find_get_pages_contig(vnode->vfs_inode.i_mapping,
+					      first, count, pv.pages);
+		ASSERTCMP(pv.nr, ==, count);
+
+		for (loop = 0; loop < count; loop++) {
+			ClearPageUptodate(pv.pages[loop]);
+			if (error)
+				SetPageError(pv.pages[loop]);
+			end_page_writeback(pv.pages[loop]);
+		}
+
+		__pagevec_release(&pv);
+	} while (first < last);
+
+	_leave("");
+}
+
+/*
+ * synchronously write back the locked page and any subsequent non-locked dirty
+ * pages also covered by the same writeback record
+ */
+static int afs_write_back_from_locked_page(struct afs_writeback *wb,
+					   struct page *primary_page)
+{
+	struct page *pages[8], *page;
+	unsigned long count;
+	unsigned n, offset, to;
+	pgoff_t start, first, last;
+	int loop, ret;
+
+	_enter(",%lx", primary_page->index);
+
+	count = 1;
+	if (!clear_page_dirty_for_io(primary_page))
+		BUG();
+	if (test_set_page_writeback(primary_page))
+		BUG();
+
+	/* find all consecutive lockable dirty pages, stopping when we find a
+	 * page that is not immediately lockable, is not dirty or is missing,
+	 * or we reach the end of the range */
+	start = primary_page->index;
+	if (start >= wb->last)
+		goto no_more;
+	start++;
+	do {
+		_debug("more %lx [%lx]", start, count);
+		n = wb->last - start + 1;
+		if (n > ARRAY_SIZE(pages))
+			n = ARRAY_SIZE(pages);
+		n = find_get_pages_contig(wb->vnode->vfs_inode.i_mapping,
+					  start, n, pages);
+		_debug("fgpc %u", n);
+		if (n == 0)
+			goto no_more;
+		if (pages[0]->index != start) {
+			for (n--; n >= 0; n--)
+				put_page(pages[n]);
+			goto no_more;
+		}
+
+		for (loop = 0; loop < n; loop++) {
+			page = pages[loop];
+			if (page->index > wb->last)
+				break;
+			if (TestSetPageLocked(page))
+				break;
+			if (!PageDirty(page) ||
+			    page_private(page) != (unsigned long) wb) {
+				unlock_page(page);
+				break;
+			}
+			if (!clear_page_dirty_for_io(page))
+				BUG();
+			if (test_set_page_writeback(page))
+				BUG();
+			unlock_page(page);
+			put_page(page);
+		}
+		count += loop;
+		if (loop < n) {
+			for (; loop < n; loop++)
+				put_page(pages[loop]);
+			goto no_more;
+		}
+
+		start += loop;
+	} while (start <= wb->last && count < 65536);
+
+no_more:
+	/* we now have a contiguous set of dirty pages, each with writeback set
+	 * and the dirty mark cleared; the first page is locked and must remain
+	 * so, all the rest are unlocked */
+	first = primary_page->index;
+	last = first + count - 1;
+
+	offset = (first == wb->first) ? wb->offset_first : 0;
+	to = (last == wb->last) ? wb->to_last : PAGE_SIZE;
+
+	_debug("write back %lx[%u..] to %lx[..%u]", first, offset, last, to);
+
+	ret = afs_vnode_store_data(wb, first, last, offset, to);
+	if (ret < 0) {
+		switch (ret) {
+		case -EDQUOT:
+		case -ENOSPC:
+			set_bit(AS_ENOSPC,
+				&wb->vnode->vfs_inode.i_mapping->flags);
+			break;
+		case -EROFS:
+		case -EIO:
+		case -EREMOTEIO:
+		case -EFBIG:
+		case -ENOENT:
+		case -ENOMEDIUM:
+		case -ENXIO:
+			afs_kill_pages(wb->vnode, true, first, last);
+			set_bit(AS_EIO, &wb->vnode->vfs_inode.i_mapping->flags);
+			break;
+		case -EACCES:
+		case -EPERM:
+		case -ENOKEY:
+		case -EKEYEXPIRED:
+		case -EKEYREJECTED:
+		case -EKEYREVOKED:
+			afs_kill_pages(wb->vnode, false, first, last);
+			break;
+		default:
+			break;
+		}
+	} else {
+		ret = count;
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * write a page back to the server
+ * - the caller locked the page for us
+ */
+int afs_writepage(struct page *page, struct writeback_control *wbc)
+{
+	struct backing_dev_info *bdi = page->mapping->backing_dev_info;
+	struct afs_writeback *wb;
+	int ret;
+
+	_enter("{%lx},", page->index);
+
+	if (wbc->sync_mode != WB_SYNC_NONE)
+		wait_on_page_writeback(page);
+
+	if (PageWriteback(page) || !PageDirty(page)) {
+		unlock_page(page);
+		return 0;
+	}
+
+	wb = (struct afs_writeback *) page_private(page);
+	ASSERT(wb != NULL);
+
+	ret = afs_write_back_from_locked_page(wb, page);
+	unlock_page(page);
+	if (ret < 0) {
+		_leave(" = %d", ret);
+		return 0;
+	}
+
+	wbc->nr_to_write -= ret;
+	if (wbc->nonblocking && bdi_write_congested(bdi))
+		wbc->encountered_congestion = 1;
+
+	_leave(" = 0");
+	return 0;
+}
+
+/*
+ * write a region of pages back to the server
+ */
+int afs_writepages_region(struct address_space *mapping,
+			  struct writeback_control *wbc,
+			  pgoff_t index, pgoff_t end, pgoff_t *_next)
+{
+	struct backing_dev_info *bdi = mapping->backing_dev_info;
+	struct afs_writeback *wb;
+	struct page *page;
+	int ret, n;
+
+	_enter(",,%lx,%lx,", index, end);
+
+	do {
+		n = find_get_pages_tag(mapping, &index, PAGECACHE_TAG_DIRTY,
+				       1, &page);
+		if (!n)
+			break;
+
+		_debug("wback %lx", page->index);
+
+		if (page->index > end) {
+			*_next = index;
+			page_cache_release(page);
+			_leave(" = 0 [%lx]", *_next);
+			return 0;
+		}
+
+		/* at this point we hold neither mapping->tree_lock nor lock on
+		 * the page itself: the page may be truncated or invalidated
+		 * (changing page->mapping to NULL), or even swizzled back from
+		 * swapper_space to tmpfs file mapping
+		 */
+		lock_page(page);
+
+		if (page->mapping != mapping) {
+			unlock_page(page);
+			page_cache_release(page);
+			continue;
+		}
+
+		if (wbc->sync_mode != WB_SYNC_NONE)
+			wait_on_page_writeback(page);
+
+		if (PageWriteback(page) || !PageDirty(page)) {
+			unlock_page(page);
+			continue;
+		}
+
+		wb = (struct afs_writeback *) page_private(page);
+		ASSERT(wb != NULL);
+
+		spin_lock(&wb->vnode->writeback_lock);
+		wb->state = AFS_WBACK_WRITING;
+		spin_unlock(&wb->vnode->writeback_lock);
+
+		ret = afs_write_back_from_locked_page(wb, page);
+		unlock_page(page);
+		page_cache_release(page);
+		if (ret < 0) {
+			_leave(" = %d", ret);
+			return ret;
+		}
+
+		wbc->nr_to_write -= ret;
+
+		if (wbc->nonblocking && bdi_write_congested(bdi)) {
+			wbc->encountered_congestion = 1;
+			break;
+		}
+
+		cond_resched();
+	} while (index < end && wbc->nr_to_write > 0);
+
+	*_next = index;
+	_leave(" = 0 [%lx]", *_next);
+	return 0;
+}
+
+/*
+ * write some of the pending data back to the server
+ */
+int afs_writepages(struct address_space *mapping,
+		   struct writeback_control *wbc)
+{
+	struct backing_dev_info *bdi = mapping->backing_dev_info;
+	pgoff_t start, end, next;
+	int ret;
+
+	_enter("");
+
+	if (wbc->nonblocking && bdi_write_congested(bdi)) {
+		wbc->encountered_congestion = 1;
+		_leave(" = 0 [congest]");
+		return 0;
+	}
+
+	if (wbc->range_cyclic) {
+		start = mapping->writeback_index;
+		end = -1;
+		ret = afs_writepages_region(mapping, wbc, start, end, &next);
+		if (start > 0 && wbc->nr_to_write > 0 && ret == 0 &&
+		    !(wbc->nonblocking && wbc->encountered_congestion))
+			ret = afs_writepages_region(mapping, wbc, 0, start,
+						    &next);
+		mapping->writeback_index = next;
+	} else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
+		end = (pgoff_t)(LLONG_MAX >> PAGE_CACHE_SHIFT);
+		ret = afs_writepages_region(mapping, wbc, 0, end, &next);
+		if (wbc->nr_to_write > 0)
+			mapping->writeback_index = next;
+	} else {
+		start = wbc->range_start >> PAGE_CACHE_SHIFT;
+		end = wbc->range_end >> PAGE_CACHE_SHIFT;
+		ret = afs_writepages_region(mapping, wbc, start, end, &next);
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * write an inode back
+ */
+int afs_write_inode(struct inode *inode, int sync)
+{
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	int ret;
+
+	_enter("{%x:%u},", vnode->fid.vid, vnode->fid.vnode);
+
+	ret = 0;
+	if (sync) {
+		ret = filemap_fdatawait(inode->i_mapping);
+		if (ret < 0)
+			__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * completion of write to server
+ */
+void afs_pages_written_back(struct afs_vnode *vnode, struct afs_call *call)
+{
+	struct afs_writeback *wb = call->wb;
+	struct pagevec pv;
+	unsigned count, loop;
+	pgoff_t first = call->first, last = call->last;
+	bool free_wb;
+
+	_enter("{%x:%u},{%lx-%lx}",
+	       vnode->fid.vid, vnode->fid.vnode, first, last);
+
+	ASSERT(wb != NULL);
+
+	pagevec_init(&pv, 0);
+
+	do {
+		_debug("attach %lx-%lx", first, last);
+
+		count = last - first + 1;
+		if (count > PAGEVEC_SIZE)
+			count = PAGEVEC_SIZE;
+		pv.nr = find_get_pages_contig(call->mapping, first, count,
+					      pv.pages);
+		ASSERTCMP(pv.nr, ==, count);
+
+		spin_lock(&vnode->writeback_lock);
+		for (loop = 0; loop < count; loop++) {
+			struct page *page = pv.pages[loop];
+			end_page_writeback(page);
+			if (page_private(page) == (unsigned long) wb) {
+				set_page_private(page, 0);
+				ClearPagePrivate(page);
+				wb->usage--;
+			}
+		}
+		free_wb = false;
+		if (wb->usage == 0) {
+			afs_unlink_writeback(wb);
+			free_wb = true;
+		}
+		spin_unlock(&vnode->writeback_lock);
+		first += count;
+		if (free_wb) {
+			afs_free_writeback(wb);
+			wb = NULL;
+		}
+
+		__pagevec_release(&pv);
+	} while (first < last);
+
+	_leave("");
+}
+
+/*
+ * write to an AFS file
+ */
+ssize_t afs_file_write(struct kiocb *iocb, const struct iovec *iov,
+		       unsigned long nr_segs, loff_t pos)
+{
+	struct dentry *dentry = iocb->ki_filp->f_path.dentry;
+	struct afs_vnode *vnode = AFS_FS_I(dentry->d_inode);
+	ssize_t result;
+	size_t count = iov_length(iov, nr_segs);
+	int ret;
+
+	_enter("{%x.%u},{%zu},%lu,",
+	       vnode->fid.vid, vnode->fid.vnode, count, nr_segs);
+
+	if (IS_SWAPFILE(&vnode->vfs_inode)) {
+		printk(KERN_INFO
+		       "AFS: Attempt to write to active swap file!\n");
+		return -EBUSY;
+	}
+
+	if (!count)
+		return 0;
+
+	result = generic_file_aio_write(iocb, iov, nr_segs, pos);
+	if (IS_ERR_VALUE(result)) {
+		_leave(" = %zd", result);
+		return result;
+	}
+
+	/* return error values for O_SYNC and IS_SYNC() */
+	if (IS_SYNC(&vnode->vfs_inode) || iocb->ki_filp->f_flags & O_SYNC) {
+		ret = afs_fsync(iocb->ki_filp, dentry, 1);
+		if (ret < 0)
+			result = ret;
+	}
+
+	_leave(" = %zd", result);
+	return result;
+}
+
+/*
+ * flush the vnode to the fileserver
+ */
+int afs_writeback_all(struct afs_vnode *vnode)
+{
+	struct address_space *mapping = vnode->vfs_inode.i_mapping;
+	struct writeback_control wbc = {
+		.bdi		= mapping->backing_dev_info,
+		.sync_mode	= WB_SYNC_ALL,
+		.nr_to_write	= LONG_MAX,
+		.for_writepages = 1,
+		.range_cyclic	= 1,
+	};
+	int ret;
+
+	_enter("");
+
+	ret = mapping->a_ops->writepages(mapping, &wbc);
+	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * flush any dirty pages for this process, and check for write errors.
+ * - the return status from this call provides a reliable indication of
+ *   whether any write errors occurred for this process.
+ */
+int afs_fsync(struct file *file, struct dentry *dentry, int datasync)
+{
+	struct afs_writeback *wb, *xwb;
+	struct afs_vnode *vnode = AFS_FS_I(dentry->d_inode);
+	int ret;
+
+	_enter("{%x:%u},{n=%s},%d",
+	       vnode->fid.vid, vnode->fid.vnode, dentry->d_name.name,
+	       datasync);
+
+	/* use a writeback record as a marker in the queue - when this reaches
+	 * the front of the queue, all the outstanding writes are either
+	 * completed or rejected */
+	wb = kzalloc(sizeof(*wb), GFP_KERNEL);
+	if (!wb)
+		return -ENOMEM;
+	wb->vnode = vnode;
+	wb->first = 0;
+	wb->last = -1;
+	wb->offset_first = 0;
+	wb->to_last = PAGE_SIZE;
+	wb->usage = 1;
+	wb->state = AFS_WBACK_SYNCING;
+	init_waitqueue_head(&wb->waitq);
+
+	spin_lock(&vnode->writeback_lock);
+	list_for_each_entry(xwb, &vnode->writebacks, link) {
+		if (xwb->state == AFS_WBACK_PENDING)
+			xwb->state = AFS_WBACK_CONFLICTING;
+	}
+	list_add_tail(&wb->link, &vnode->writebacks);
+	spin_unlock(&vnode->writeback_lock);
+
+	/* push all the outstanding writebacks to the server */
+	ret = afs_writeback_all(vnode);
+	if (ret < 0) {
+		afs_put_writeback(wb);
+		_leave(" = %d [wb]", ret);
+		return ret;
+	}
+
+	/* wait for the preceding writes to actually complete */
+	ret = wait_event_interruptible(wb->waitq,
+				       wb->state == AFS_WBACK_COMPLETE ||
+				       vnode->writebacks.next == &wb->link);
+	afs_put_writeback(wb);
+	_leave(" = %d", ret);
+	return ret;
+}