AFS: implement basic file write support

Implement support for writing to regular AFS files, including:

 (1) write

 (2) truncate

 (3) fsync, fdatasync

 (4) chmod, chown, chgrp, utime.

AFS writeback attempts to batch writes into as chunks as large as it can manage
up to the point that it writes back 65535 pages in one chunk or it meets a
locked page.

Furthermore, if a page has been written to using a particular key, then should
another write to that page use some other key, the first write will be flushed
before the second is allowed to take place.  If the first write fails due to a
security error, then the page will be scrapped and reread before the second
write takes place.

If a page is dirty and the callback on it is broken by the server, then the
dirty data is not discarded (same behaviour as NFS).

Shared-writable mappings are not supported by this patch.

[akpm@linux-foundation.org: fix a bunch of warnings]
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 835 insertions, 0 deletions

diff --git a/fs/afs/write.c b/fs/afs/write.c
new file mode 100644
index 000000000000..83ff29262816
--- /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;
+}