// SPDX-License-Identifier: GPL-2.0-or-later
/* 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)
 */

#include <linux/backing-dev.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include "internal.h"

/*
 * 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);
}

/*
 * partly or wholly fill a page that's under preparation for writing
 */
static int afs_fill_page(struct afs_vnode *vnode, struct key *key,
                         loff_t pos, unsigned int len, struct page *page)
{
        struct afs_read *req;
        size_t p;
        void *data;
        int ret;

        _enter(",,%llu", (unsigned long long)pos);

        if (pos >= vnode->vfs_inode.i_size) {
                p = pos & ~PAGE_MASK;
                ASSERTCMP(p + len, <=, PAGE_SIZE);
                data = kmap(page);
                memset(data + p, 0, len);
                kunmap(page);
                return 0;
        }

        req = kzalloc(struct_size(req, array, 1), GFP_KERNEL);
        if (!req)
                return -ENOMEM;

        refcount_set(&req->usage, 1);
        req->pos = pos;
        req->len = len;
        req->nr_pages = 1;
        req->pages = req->array;
        req->pages[0] = page;
        get_page(page);

        ret = afs_fetch_data(vnode, key, req);
        afs_put_read(req);
        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 to perform part of a write to a page
 */
int afs_write_begin(struct file *file, struct address_space *mapping,
                    loff_t pos, unsigned len, unsigned flags,
                    struct page **pagep, void **fsdata)
{
        struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
        struct page *page;
        struct key *key = afs_file_key(file);
        unsigned long priv;
        unsigned f, from = pos & (PAGE_SIZE - 1);
        unsigned t, to = from + len;
        pgoff_t index = pos >> PAGE_SHIFT;
        int ret;

        _enter("{%llx:%llu},{%lx},%u,%u",
               vnode->fid.vid, vnode->fid.vnode, index, from, to);

        /* We want to store information about how much of a page is altered in
         * page->private.
         */
        BUILD_BUG_ON(PAGE_SIZE > 32768 && sizeof(page->private) < 8);

        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page)
                return -ENOMEM;

        if (!PageUptodate(page) && len != PAGE_SIZE) {
                ret = afs_fill_page(vnode, key, pos & PAGE_MASK, PAGE_SIZE, page);
                if (ret < 0) {
                        unlock_page(page);
                        put_page(page);
                        _leave(" = %d [prep]", ret);
                        return ret;
                }
                SetPageUptodate(page);
        }

        /* page won't leak in error case: it eventually gets cleaned off LRU */
        *pagep = page;

try_again:
        /* See if this page is already partially written in a way that we can
         * merge the new write with.
         */
        t = f = 0;
        if (PagePrivate(page)) {
                priv = page_private(page);
                f = priv & AFS_PRIV_MAX;
                t = priv >> AFS_PRIV_SHIFT;
                ASSERTCMP(f, <=, t);
        }

        if (f != t) {
                if (PageWriteback(page)) {
                        trace_afs_page_dirty(vnode, tracepoint_string("alrdy"),
                                             page->index, priv);
                        goto flush_conflicting_write;
                }
                /* If the file is being filled locally, allow inter-write
                 * spaces to be merged into writes.  If it's not, only write
                 * back what the user gives us.
                 */
                if (!test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags) &&
                    (to < f || from > t))
                        goto flush_conflicting_write;
                if (from < f)
                        f = from;
                if (to > t)
                        t = to;
        } else {
                f = from;
                t = to;
        }

        priv = (unsigned long)t << AFS_PRIV_SHIFT;
        priv |= f;
        trace_afs_page_dirty(vnode, tracepoint_string("begin"),
                             page->index, priv);
        SetPagePrivate(page);
        set_page_private(page, priv);
        _leave(" = 0");
        return 0;

        /* The previous write and this write aren't adjacent or overlapping, so
         * flush the page out.
         */
flush_conflicting_write:
        _debug("flush conflict");
        ret = write_one_page(page);
        if (ret < 0) {
                _leave(" = %d", ret);
                return ret;
        }

        ret = lock_page_killable(page);
        if (ret < 0) {
                _leave(" = %d", ret);
                return ret;
        }
        goto try_again;
}

/*
 * finalise part of a write to a page
 */
int afs_write_end(struct file *file, struct address_space *mapping,
                  loff_t pos, unsigned len, unsigned copied,
                  struct page *page, void *fsdata)
{
        struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
        struct key *key = afs_file_key(file);
        loff_t i_size, maybe_i_size;
        int ret;

        _enter("{%llx:%llu},{%lx}",
               vnode->fid.vid, vnode->fid.vnode, page->index);

        maybe_i_size = pos + copied;

        i_size = i_size_read(&vnode->vfs_inode);
        if (maybe_i_size > i_size) {
                write_seqlock(&vnode->cb_lock);
                i_size = i_size_read(&vnode->vfs_inode);
                if (maybe_i_size > i_size)
                        i_size_write(&vnode->vfs_inode, maybe_i_size);
                write_sequnlock(&vnode->cb_lock);
        }

        if (!PageUptodate(page)) {
                if (copied < len) {
                        /* Try and load any missing data from the server.  The
                         * unmarshalling routine will take care of clearing any
                         * bits that are beyond the EOF.
                         */
                        ret = afs_fill_page(vnode, key, pos + copied,
                                            len - copied, page);
                        if (ret < 0)
                                goto out;
                }
                SetPageUptodate(page);
        }

        set_page_dirty(page);
        if (PageDirty(page))
                _debug("dirtied");
        ret = copied;

out:
        unlock_page(page);
        put_page(page);
        return ret;
}

/*
 * kill all the pages in the given range
 */
static void afs_kill_pages(struct address_space *mapping,
                           pgoff_t first, pgoff_t last)
{
        struct afs_vnode *vnode = AFS_FS_I(mapping->host);
        struct pagevec pv;
        unsigned count, loop;

        _enter("{%llx:%llu},%lx-%lx",
               vnode->fid.vid, vnode->fid.vnode, first, last);

        pagevec_init(&pv);

        do {
                _debug("kill %lx-%lx", first, last);

                count = last - first + 1;
                if (count > PAGEVEC_SIZE)
                        count = PAGEVEC_SIZE;
                pv.nr = find_get_pages_contig(mapping, first, count, pv.pages);
                ASSERTCMP(pv.nr, ==, count);

                for (loop = 0; loop < count; loop++) {
                        struct page *page = pv.pages[loop];
                        ClearPageUptodate(page);
                        SetPageError(page);
                        end_page_writeback(page);
                        if (page->index >= first)
                                first = page->index + 1;
                        lock_page(page);
                        generic_error_remove_page(mapping, page);
                        unlock_page(page);
                }

                __pagevec_release(&pv);
        } while (first <= last);

        _leave("");
}

/*
 * Redirty all the pages in a given range.
 */
static void afs_redirty_pages(struct writeback_control *wbc,
                              struct address_space *mapping,
                              pgoff_t first, pgoff_t last)
{
        struct afs_vnode *vnode = AFS_FS_I(mapping->host);
        struct pagevec pv;
        unsigned count, loop;

        _enter("{%llx:%llu},%lx-%lx",
               vnode->fid.vid, vnode->fid.vnode, first, last);

        pagevec_init(&pv);

        do {
                _debug("redirty %lx-%lx", first, last);

                count = last - first + 1;
                if (count > PAGEVEC_SIZE)
                        count = PAGEVEC_SIZE;
                pv.nr = find_get_pages_contig(mapping, first, count, pv.pages);
                ASSERTCMP(pv.nr, ==, count);

                for (loop = 0; loop < count; loop++) {
                        struct page *page = pv.pages[loop];

                        redirty_page_for_writepage(wbc, page);
                        end_page_writeback(page);
                        if (page->index >= first)
                                first = page->index + 1;
                }

                __pagevec_release(&pv);
        } while (first <= last);

        _leave("");
}

/*
 * completion of write to server
 */
static void afs_pages_written_back(struct afs_vnode *vnode,
                                   pgoff_t first, pgoff_t last)
{
        struct pagevec pv;
        unsigned long priv;
        unsigned count, loop;

        _enter("{%llx:%llu},{%lx-%lx}",
               vnode->fid.vid, vnode->fid.vnode, first, last);

        pagevec_init(&pv);

        do {
                _debug("done %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++) {
                        priv = page_private(pv.pages[loop]);
                        trace_afs_page_dirty(vnode, tracepoint_string("clear"),
                                             pv.pages[loop]->index, priv);
                        set_page_private(pv.pages[loop], 0);
                        end_page_writeback(pv.pages[loop]);
                }
                first += count;
                __pagevec_release(&pv);
        } while (first <= last);

        afs_prune_wb_keys(vnode);
        _leave("");
}

/*
 * Find a key to use for the writeback.  We cached the keys used to author the
 * writes on the vnode.  *_wbk will contain the last writeback key used or NULL
 * and we need to start from there if it's set.
 */
static int afs_get_writeback_key(struct afs_vnode *vnode,
                                 struct afs_wb_key **_wbk)
{
        struct afs_wb_key *wbk = NULL;
        struct list_head *p;
        int ret = -ENOKEY, ret2;

        spin_lock(&vnode->wb_lock);
        if (*_wbk)
                p = (*_wbk)->vnode_link.next;
        else
                p = vnode->wb_keys.next;

        while (p != &vnode->wb_keys) {
                wbk = list_entry(p, struct afs_wb_key, vnode_link);
                _debug("wbk %u", key_serial(wbk->key));
                ret2 = key_validate(wbk->key);
                if (ret2 == 0) {
                        refcount_inc(&wbk->usage);
                        _debug("USE WB KEY %u", key_serial(wbk->key));
                        break;
                }

                wbk = NULL;
                if (ret == -ENOKEY)
                        ret = ret2;
                p = p->next;
        }

        spin_unlock(&vnode->wb_lock);
        if (*_wbk)
                afs_put_wb_key(*_wbk);
        *_wbk = wbk;
        return 0;
}

static void afs_store_data_success(struct afs_operation *op)
{
        struct afs_vnode *vnode = op->file[0].vnode;

        op->ctime = op->file[0].scb.status.mtime_client;
        afs_vnode_commit_status(op, &op->file[0]);
        if (op->error == 0) {
                afs_pages_written_back(vnode, op->store.first, op->store.last);
                afs_stat_v(vnode, n_stores);
                atomic_long_add((op->store.last * PAGE_SIZE + op->store.last_to) -
                                (op->store.first * PAGE_SIZE + op->store.first_offset),
                                &afs_v2net(vnode)->n_store_bytes);
        }
}

static const struct afs_operation_ops afs_store_data_operation = {
        .issue_afs_rpc  = afs_fs_store_data,
        .issue_yfs_rpc  = yfs_fs_store_data,
        .success        = afs_store_data_success,
};

/*
 * write to a file
 */
static int afs_store_data(struct address_space *mapping,
                          pgoff_t first, pgoff_t last,
                          unsigned offset, unsigned to)
{
        struct afs_vnode *vnode = AFS_FS_I(mapping->host);
        struct afs_operation *op;
        struct afs_wb_key *wbk = NULL;
        int ret;

        _enter("%s{%llx:%llu.%u},%lx,%lx,%x,%x",
               vnode->volume->name,
               vnode->fid.vid,
               vnode->fid.vnode,
               vnode->fid.unique,
               first, last, offset, to);

        ret = afs_get_writeback_key(vnode, &wbk);
        if (ret) {
                _leave(" = %d [no keys]", ret);
                return ret;
        }

        op = afs_alloc_operation(wbk->key, vnode->volume);
        if (IS_ERR(op)) {
                afs_put_wb_key(wbk);
                return -ENOMEM;
        }

        afs_op_set_vnode(op, 0, vnode);
        op->file[0].dv_delta = 1;
        op->store.mapping = mapping;
        op->store.first = first;
        op->store.last = last;
        op->store.first_offset = offset;
        op->store.last_to = to;
        op->mtime = vnode->vfs_inode.i_mtime;
        op->flags |= AFS_OPERATION_UNINTR;
        op->ops = &afs_store_data_operation;

try_next_key:
        afs_begin_vnode_operation(op);
        afs_wait_for_operation(op);

        switch (op->error) {
        case -EACCES:
        case -EPERM:
        case -ENOKEY:
        case -EKEYEXPIRED:
        case -EKEYREJECTED:
        case -EKEYREVOKED:
                _debug("next");

                ret = afs_get_writeback_key(vnode, &wbk);
                if (ret == 0) {
                        key_put(op->key);
                        op->key = key_get(wbk->key);
                        goto try_next_key;
                }
                break;
        }

        afs_put_wb_key(wbk);
        _leave(" = %d", op->error);
        return afs_put_operation(op);
}

/*
 * Synchronously write back the locked page and any subsequent non-locked dirty
 * pages.
 */
static int afs_write_back_from_locked_page(struct address_space *mapping,
                                           struct writeback_control *wbc,
                                           struct page *primary_page,
                                           pgoff_t final_page)
{
        struct afs_vnode *vnode = AFS_FS_I(mapping->host);
        struct page *pages[8], *page;
        unsigned long count, priv;
        unsigned n, offset, to, f, t;
        pgoff_t start, first, last;
        loff_t i_size, end;
        int loop, ret;

        _enter(",%lx", primary_page->index);

        count = 1;
        if (test_set_page_writeback(primary_page))
                BUG();

        /* Find all consecutive lockable dirty pages that have contiguous
         * written regions, 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;
        priv = page_private(primary_page);
        offset = priv & AFS_PRIV_MAX;
        to = priv >> AFS_PRIV_SHIFT;
        trace_afs_page_dirty(vnode, tracepoint_string("store"),
                             primary_page->index, priv);

        WARN_ON(offset == to);
        if (offset == to)
                trace_afs_page_dirty(vnode, tracepoint_string("WARN"),
                                     primary_page->index, priv);

        if (start >= final_page ||
            (to < PAGE_SIZE && !test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags)))
                goto no_more;

        start++;
        do {
                _debug("more %lx [%lx]", start, count);
                n = final_page - start + 1;
                if (n > ARRAY_SIZE(pages))
                        n = ARRAY_SIZE(pages);
                n = find_get_pages_contig(mapping, start, ARRAY_SIZE(pages), pages);
                _debug("fgpc %u", n);
                if (n == 0)
                        goto no_more;
                if (pages[0]->index != start) {
                        do {
                                put_page(pages[--n]);
                        } while (n > 0);
                        goto no_more;
                }

                for (loop = 0; loop < n; loop++) {
                        page = pages[loop];
                        if (to != PAGE_SIZE &&
                            !test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags))
                                break;
                        if (page->index > final_page)
                                break;
                        if (!trylock_page(page))
                                break;
                        if (!PageDirty(page) || PageWriteback(page)) {
                                unlock_page(page);
                                break;
                        }

                        priv = page_private(page);
                        f = priv & AFS_PRIV_MAX;
                        t = priv >> AFS_PRIV_SHIFT;
                        if (f != 0 &&
                            !test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags)) {
                                unlock_page(page);
                                break;
                        }
                        to = t;

                        trace_afs_page_dirty(vnode, tracepoint_string("store+"),
                                             page->index, priv);

                        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 <= final_page && count < 65536);

no_more:
        /* We now have a contiguous set of dirty pages, each with writeback
         * set; the first page is still locked at this point, but all the rest
         * have been unlocked.
         */
        unlock_page(primary_page);

        first = primary_page->index;
        last = first + count - 1;

        end = (loff_t)last * PAGE_SIZE + to;
        i_size = i_size_read(&vnode->vfs_inode);

        _debug("write back %lx[%u..] to %lx[..%u]", first, offset, last, to);
        if (end > i_size)
                to = i_size & ~PAGE_MASK;

        ret = afs_store_data(mapping, first, last, offset, to);
        switch (ret) {
        case 0:
                ret = count;
                break;

        default:
                pr_notice("kAFS: Unexpected error from FS.StoreData %d\n", ret);
                fallthrough;
        case -EACCES:
        case -EPERM:
        case -ENOKEY:
        case -EKEYEXPIRED:
        case -EKEYREJECTED:
        case -EKEYREVOKED:
                afs_redirty_pages(wbc, mapping, first, last);
                mapping_set_error(mapping, ret);
                break;

        case -EDQUOT:
        case -ENOSPC:
                afs_redirty_pages(wbc, mapping, first, last);
                mapping_set_error(mapping, -ENOSPC);
                break;

        case -EROFS:
        case -EIO:
        case -EREMOTEIO:
        case -EFBIG:
        case -ENOENT:
        case -ENOMEDIUM:
        case -ENXIO:
                trace_afs_file_error(vnode, ret, afs_file_error_writeback_fail);
                afs_kill_pages(mapping, first, last);
                mapping_set_error(mapping, ret);
                break;
        }

        _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)
{
        int ret;

        _enter("{%lx},", page->index);

        ret = afs_write_back_from_locked_page(page->mapping, wbc, page,
                                              wbc->range_end >> PAGE_SHIFT);
        if (ret < 0) {
                _leave(" = %d", ret);
                return 0;
        }

        wbc->nr_to_write -= ret;

        _leave(" = 0");
        return 0;
}

/*
 * write a region of pages back to the server
 */
static int afs_writepages_region(struct address_space *mapping,
                                 struct writeback_control *wbc,
                                 pgoff_t index, pgoff_t end, pgoff_t *_next)
{
        struct page *page;
        int ret, n;

        _enter(",,%lx,%lx,", index, end);

        do {
                n = find_get_pages_range_tag(mapping, &index, end,
                                        PAGECACHE_TAG_DIRTY, 1, &page);
                if (!n)
                        break;

                _debug("wback %lx", page->index);

                /*
                 * at this point we hold neither the i_pages lock nor the
                 * page lock: the page may be truncated or invalidated
                 * (changing page->mapping to NULL), or even swizzled
                 * back from swapper_space to tmpfs file mapping
                 */
                ret = lock_page_killable(page);
                if (ret < 0) {
                        put_page(page);
                        _leave(" = %d", ret);
                        return ret;
                }

                if (page->mapping != mapping || !PageDirty(page)) {
                        unlock_page(page);
                        put_page(page);
                        continue;
                }

                if (PageWriteback(page)) {
                        unlock_page(page);
                        if (wbc->sync_mode != WB_SYNC_NONE)
                                wait_on_page_writeback(page);
                        put_page(page);
                        continue;
                }

                if (!clear_page_dirty_for_io(page))
                        BUG();
                ret = afs_write_back_from_locked_page(mapping, wbc, page, end);
                put_page(page);
                if (ret < 0) {
                        _leave(" = %d", ret);
                        return ret;
                }

                wbc->nr_to_write -= ret;

                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 afs_vnode *vnode = AFS_FS_I(mapping->host);
        pgoff_t start, end, next;
        int ret;

        _enter("");

        /* We have to be careful as we can end up racing with setattr()
         * truncating the pagecache since the caller doesn't take a lock here
         * to prevent it.
         */
        if (wbc->sync_mode == WB_SYNC_ALL)
                down_read(&vnode->validate_lock);
        else if (!down_read_trylock(&vnode->validate_lock))
                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)
                        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_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_SHIFT;
                end = wbc->range_end >> PAGE_SHIFT;
                ret = afs_writepages_region(mapping, wbc, start, end, &next);
        }

        up_read(&vnode->validate_lock);
        _leave(" = %d", ret);
        return ret;
}

/*
 * write to an AFS file
 */
ssize_t afs_file_write(struct kiocb *iocb, struct iov_iter *from)
{
        struct afs_vnode *vnode = AFS_FS_I(file_inode(iocb->ki_filp));
        ssize_t result;
        size_t count = iov_iter_count(from);

        _enter("{%llx:%llu},{%zu},",
               vnode->fid.vid, vnode->fid.vnode, count);

        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_write_iter(iocb, from);

        _leave(" = %zd", result);
        return result;
}

/*
 * 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, loff_t start, loff_t end, int datasync)
{
        struct inode *inode = file_inode(file);
        struct afs_vnode *vnode = AFS_FS_I(inode);

        _enter("{%llx:%llu},{n=%pD},%d",
               vnode->fid.vid, vnode->fid.vnode, file,
               datasync);

        return file_write_and_wait_range(file, start, end);
}

/*
 * notification that a previously read-only page is about to become writable
 * - if it returns an error, the caller will deliver a bus error signal
 */
vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
{
        struct file *file = vmf->vma->vm_file;
        struct inode *inode = file_inode(file);
        struct afs_vnode *vnode = AFS_FS_I(inode);
        unsigned long priv;

        _enter("{{%llx:%llu}},{%lx}",
               vnode->fid.vid, vnode->fid.vnode, vmf->page->index);

        sb_start_pagefault(inode->i_sb);

        /* Wait for the page to be written to the cache before we allow it to
         * be modified.  We then assume the entire page will need writing back.
         */
#ifdef CONFIG_AFS_FSCACHE
        fscache_wait_on_page_write(vnode->cache, vmf->page);
#endif

        if (PageWriteback(vmf->page) &&
            wait_on_page_bit_killable(vmf->page, PG_writeback) < 0)
                return VM_FAULT_RETRY;

        if (lock_page_killable(vmf->page) < 0)
                return VM_FAULT_RETRY;

        /* We mustn't change page->private until writeback is complete as that
         * details the portion of the page we need to write back and we might
         * need to redirty the page if there's a problem.
         */
        wait_on_page_writeback(vmf->page);

        priv = (unsigned long)PAGE_SIZE << AFS_PRIV_SHIFT; /* To */
        priv |= 0; /* From */
        trace_afs_page_dirty(vnode, tracepoint_string("mkwrite"),
                             vmf->page->index, priv);
        SetPagePrivate(vmf->page);
        set_page_private(vmf->page, priv);
        file_update_time(file);

        sb_end_pagefault(inode->i_sb);
        return VM_FAULT_LOCKED;
}

/*
 * Prune the keys cached for writeback.  The caller must hold vnode->wb_lock.
 */
void afs_prune_wb_keys(struct afs_vnode *vnode)
{
        LIST_HEAD(graveyard);
        struct afs_wb_key *wbk, *tmp;

        /* Discard unused keys */
        spin_lock(&vnode->wb_lock);

        if (!mapping_tagged(&vnode->vfs_inode.i_data, PAGECACHE_TAG_WRITEBACK) &&
            !mapping_tagged(&vnode->vfs_inode.i_data, PAGECACHE_TAG_DIRTY)) {
                list_for_each_entry_safe(wbk, tmp, &vnode->wb_keys, vnode_link) {
                        if (refcount_read(&wbk->usage) == 1)
                                list_move(&wbk->vnode_link, &graveyard);
                }
        }

        spin_unlock(&vnode->wb_lock);

        while (!list_empty(&graveyard)) {
                wbk = list_entry(graveyard.next, struct afs_wb_key, vnode_link);
                list_del(&wbk->vnode_link);
                afs_put_wb_key(wbk);
        }
}

/*
 * Clean up a page during invalidation.
 */
int afs_launder_page(struct page *page)
{
        struct address_space *mapping = page->mapping;
        struct afs_vnode *vnode = AFS_FS_I(mapping->host);
        unsigned long priv;
        unsigned int f, t;
        int ret = 0;

        _enter("{%lx}", page->index);

        priv = page_private(page);
        if (clear_page_dirty_for_io(page)) {
                f = 0;
                t = PAGE_SIZE;
                if (PagePrivate(page)) {
                        f = priv & AFS_PRIV_MAX;
                        t = priv >> AFS_PRIV_SHIFT;
                }

                trace_afs_page_dirty(vnode, tracepoint_string("launder"),
                                     page->index, priv);
                ret = afs_store_data(mapping, page->index, page->index, t, f);
        }

        trace_afs_page_dirty(vnode, tracepoint_string("laundered"),
                             page->index, priv);
        set_page_private(page, 0);
        ClearPagePrivate(page);

#ifdef CONFIG_AFS_FSCACHE
        if (PageFsCache(page)) {
                fscache_wait_on_page_write(vnode->cache, page);
                fscache_uncache_page(vnode->cache, page);
        }
#endif
        return ret;
}