page.c

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/* Cache page management and data I/O routines
 *
 * Copyright (C) 2004-2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * 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.
 */

#define FSCACHE_DEBUG_LEVEL PAGE
#include <linux/module.h>
#include <linux/fscache-cache.h>
#include <linux/buffer_head.h>
#include <linux/pagevec.h>
#include <linux/slab.h>
#include "internal.h"

/*
 * check to see if a page is being written to the cache
 */
bool __fscache_check_page_write(struct fscache_cookie *cookie, struct page *page)
{
    void *val;

    rcu_read_lock();
    val = radix_tree_lookup(&cookie->stores, page->index);
    rcu_read_unlock();

    return val != NULL;
}
EXPORT_SYMBOL(__fscache_check_page_write);

/*
 * wait for a page to finish being written to the cache
 */
void __fscache_wait_on_page_write(struct fscache_cookie *cookie, struct page *page)
{
    wait_queue_head_t *wq = bit_waitqueue(&cookie->flags, 0);

    wait_event(*wq, !__fscache_check_page_write(cookie, page));
}
EXPORT_SYMBOL(__fscache_wait_on_page_write);

/*
 * decide whether a page can be released, possibly by cancelling a store to it
 * - we're allowed to sleep if __GFP_WAIT is flagged
 */
bool __fscache_maybe_release_page(struct fscache_cookie *cookie,
                  struct page *page,
                  gfp_t gfp)
{
    struct page *xpage;
    void *val;

    _enter("%p,%p,%x", cookie, page, gfp);

    rcu_read_lock();
    val = radix_tree_lookup(&cookie->stores, page->index);
    if (!val) {
        rcu_read_unlock();
        fscache_stat(&fscache_n_store_vmscan_not_storing);
        __fscache_uncache_page(cookie, page);
        return true;
    }

    /* see if the page is actually undergoing storage - if so we can't get
     * rid of it till the cache has finished with it */
    if (radix_tree_tag_get(&cookie->stores, page->index,
                   FSCACHE_COOKIE_STORING_TAG)) {
        rcu_read_unlock();
        goto page_busy;
    }

    /* the page is pending storage, so we attempt to cancel the store and
     * discard the store request so that the page can be reclaimed */
    spin_lock(&cookie->stores_lock);
    rcu_read_unlock();

    if (radix_tree_tag_get(&cookie->stores, page->index,
                   FSCACHE_COOKIE_STORING_TAG)) {
        /* the page started to undergo storage whilst we were looking,
         * so now we can only wait or return */
        spin_unlock(&cookie->stores_lock);
        goto page_busy;
    }

    xpage = radix_tree_delete(&cookie->stores, page->index);
    spin_unlock(&cookie->stores_lock);

    if (xpage) {
        fscache_stat(&fscache_n_store_vmscan_cancelled);
        fscache_stat(&fscache_n_store_radix_deletes);
        ASSERTCMP(xpage, ==, page);
    } else {
        fscache_stat(&fscache_n_store_vmscan_gone);
    }

    wake_up_bit(&cookie->flags, 0);
    if (xpage)
        page_cache_release(xpage);
    __fscache_uncache_page(cookie, page);
    return true;

page_busy:
    /* we might want to wait here, but that could deadlock the allocator as
     * the work threads writing to the cache may all end up sleeping
     * on memory allocation */
    fscache_stat(&fscache_n_store_vmscan_busy);
    return false;
}
EXPORT_SYMBOL(__fscache_maybe_release_page);

/*
 * note that a page has finished being written to the cache
 */
static void fscache_end_page_write(struct fscache_object *object,
                   struct page *page)
{
    struct fscache_cookie *cookie;
    struct page *xpage = NULL;

    spin_lock(&object->lock);
    cookie = object->cookie;
    if (cookie) {
        /* delete the page from the tree if it is now no longer
         * pending */
        spin_lock(&cookie->stores_lock);
        radix_tree_tag_clear(&cookie->stores, page->index,
                     FSCACHE_COOKIE_STORING_TAG);
        if (!radix_tree_tag_get(&cookie->stores, page->index,
                    FSCACHE_COOKIE_PENDING_TAG)) {
            fscache_stat(&fscache_n_store_radix_deletes);
            xpage = radix_tree_delete(&cookie->stores, page->index);
        }
        spin_unlock(&cookie->stores_lock);
        wake_up_bit(&cookie->flags, 0);
    }
    spin_unlock(&object->lock);
    if (xpage)
        page_cache_release(xpage);
}

/*
 * actually apply the changed attributes to a cache object
 */
static void fscache_attr_changed_op(struct fscache_operation *op)
{
    struct fscache_object *object = op->object;
    int ret;

    _enter("{OBJ%x OP%x}", object->debug_id, op->debug_id);

    fscache_stat(&fscache_n_attr_changed_calls);

    if (fscache_object_is_active(object)) {
        fscache_stat(&fscache_n_cop_attr_changed);
        ret = object->cache->ops->attr_changed(object);
        fscache_stat_d(&fscache_n_cop_attr_changed);
        if (ret < 0)
            fscache_abort_object(object);
    }

    _leave("");
}

/*
 * notification that the attributes on an object have changed
 */
int __fscache_attr_changed(struct fscache_cookie *cookie)
{
    struct fscache_operation *op;
    struct fscache_object *object;

    _enter("%p", cookie);

    ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);

    fscache_stat(&fscache_n_attr_changed);

    op = kzalloc(sizeof(*op), GFP_KERNEL);
    if (!op) {
        fscache_stat(&fscache_n_attr_changed_nomem);
        _leave(" = -ENOMEM");
        return -ENOMEM;
    }

    fscache_operation_init(op, fscache_attr_changed_op, NULL);
    op->flags = FSCACHE_OP_ASYNC | (1 << FSCACHE_OP_EXCLUSIVE);

    spin_lock(&cookie->lock);

    if (hlist_empty(&cookie->backing_objects))
        goto nobufs;
    object = hlist_entry(cookie->backing_objects.first,
                 struct fscache_object, cookie_link);

    if (fscache_submit_exclusive_op(object, op) < 0)
        goto nobufs;
    spin_unlock(&cookie->lock);
    fscache_stat(&fscache_n_attr_changed_ok);
    fscache_put_operation(op);
    _leave(" = 0");
    return 0;

nobufs:
    spin_unlock(&cookie->lock);
    kfree(op);
    fscache_stat(&fscache_n_attr_changed_nobufs);
    _leave(" = %d", -ENOBUFS);
    return -ENOBUFS;
}
EXPORT_SYMBOL(__fscache_attr_changed);

/*
 * release a retrieval op reference
 */
static void fscache_release_retrieval_op(struct fscache_operation *_op)
{
    struct fscache_retrieval *op =
        container_of(_op, struct fscache_retrieval, op);

    _enter("{OP%x}", op->op.debug_id);

    fscache_hist(fscache_retrieval_histogram, op->start_time);
    if (op->context)
        fscache_put_context(op->op.object->cookie, op->context);

    _leave("");
}

/*
 * allocate a retrieval op
 */
static struct fscache_retrieval *fscache_alloc_retrieval(
    struct address_space *mapping,
    fscache_rw_complete_t end_io_func,
    void *context)
{
    struct fscache_retrieval *op;

    /* allocate a retrieval operation and attempt to submit it */
    op = kzalloc(sizeof(*op), GFP_NOIO);
    if (!op) {
        fscache_stat(&fscache_n_retrievals_nomem);
        return NULL;
    }

    fscache_operation_init(&op->op, NULL, fscache_release_retrieval_op);
    op->op.flags    = FSCACHE_OP_MYTHREAD | (1 << FSCACHE_OP_WAITING);
    op->mapping = mapping;
    op->end_io_func = end_io_func;
    op->context = context;
    op->start_time  = jiffies;
    INIT_LIST_HEAD(&op->to_do);
    return op;
}

/*
 * wait for a deferred lookup to complete
 */
static int fscache_wait_for_deferred_lookup(struct fscache_cookie *cookie)
{
    unsigned long jif;

    _enter("");

    if (!test_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags)) {
        _leave(" = 0 [imm]");
        return 0;
    }

    fscache_stat(&fscache_n_retrievals_wait);

    jif = jiffies;
    if (wait_on_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP,
            fscache_wait_bit_interruptible,
            TASK_INTERRUPTIBLE) != 0) {
        fscache_stat(&fscache_n_retrievals_intr);
        _leave(" = -ERESTARTSYS");
        return -ERESTARTSYS;
    }

    ASSERT(!test_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags));

    smp_rmb();
    fscache_hist(fscache_retrieval_delay_histogram, jif);
    _leave(" = 0 [dly]");
    return 0;
}

/*
 * wait for an object to become active (or dead)
 */
static int fscache_wait_for_retrieval_activation(struct fscache_object *object,
                         struct fscache_retrieval *op,
                         atomic_t *stat_op_waits,
                         atomic_t *stat_object_dead)
{
    int ret;

    if (!test_bit(FSCACHE_OP_WAITING, &op->op.flags))
        goto check_if_dead;

    _debug(">>> WT");
    fscache_stat(stat_op_waits);
    if (wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
            fscache_wait_bit_interruptible,
            TASK_INTERRUPTIBLE) < 0) {
        ret = fscache_cancel_op(&op->op);
        if (ret == 0)
            return -ERESTARTSYS;

        /* it's been removed from the pending queue by another party,
         * so we should get to run shortly */
        wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
                fscache_wait_bit, TASK_UNINTERRUPTIBLE);
    }
    _debug("<<< GO");

check_if_dead:
    if (unlikely(fscache_object_is_dead(object))) {
        fscache_stat(stat_object_dead);
        return -ENOBUFS;
    }
    return 0;
}

/*
 * read a page from the cache or allocate a block in which to store it
 * - we return:
 *   -ENOMEM    - out of memory, nothing done
 *   -ERESTARTSYS - interrupted
 *   -ENOBUFS   - no backing object available in which to cache the block
 *   -ENODATA   - no data available in the backing object for this block
 *   0      - dispatched a read - it'll call end_io_func() when finished
 */
int __fscache_read_or_alloc_page(struct fscache_cookie *cookie,
                 struct page *page,
                 fscache_rw_complete_t end_io_func,
                 void *context,
                 gfp_t gfp)
{
    struct fscache_retrieval *op;
    struct fscache_object *object;
    int ret;

    _enter("%p,%p,,,", cookie, page);

    fscache_stat(&fscache_n_retrievals);

    if (hlist_empty(&cookie->backing_objects))
        goto nobufs;

    ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
    ASSERTCMP(page, !=, NULL);

    if (fscache_wait_for_deferred_lookup(cookie) < 0)
        return -ERESTARTSYS;

    op = fscache_alloc_retrieval(page->mapping, end_io_func, context);
    if (!op) {
        _leave(" = -ENOMEM");
        return -ENOMEM;
    }

    spin_lock(&cookie->lock);

    if (hlist_empty(&cookie->backing_objects))
        goto nobufs_unlock;
    object = hlist_entry(cookie->backing_objects.first,
                 struct fscache_object, cookie_link);

    ASSERTCMP(object->state, >, FSCACHE_OBJECT_LOOKING_UP);

    atomic_inc(&object->n_reads);
    set_bit(FSCACHE_OP_DEC_READ_CNT, &op->op.flags);

    if (fscache_submit_op(object, &op->op) < 0)
        goto nobufs_unlock;
    spin_unlock(&cookie->lock);

    fscache_stat(&fscache_n_retrieval_ops);

    /* pin the netfs read context in case we need to do the actual netfs
     * read because we've encountered a cache read failure */
    fscache_get_context(object->cookie, op->context);

    /* we wait for the operation to become active, and then process it
     * *here*, in this thread, and not in the thread pool */
    ret = fscache_wait_for_retrieval_activation(
        object, op,
        __fscache_stat(&fscache_n_retrieval_op_waits),
        __fscache_stat(&fscache_n_retrievals_object_dead));
    if (ret < 0)
        goto error;

    /* ask the cache to honour the operation */
    if (test_bit(FSCACHE_COOKIE_NO_DATA_YET, &object->cookie->flags)) {
        fscache_stat(&fscache_n_cop_allocate_page);
        ret = object->cache->ops->allocate_page(op, page, gfp);
        fscache_stat_d(&fscache_n_cop_allocate_page);
        if (ret == 0)
            ret = -ENODATA;
    } else {
        fscache_stat(&fscache_n_cop_read_or_alloc_page);
        ret = object->cache->ops->read_or_alloc_page(op, page, gfp);
        fscache_stat_d(&fscache_n_cop_read_or_alloc_page);
    }

error:
    if (ret == -ENOMEM)
        fscache_stat(&fscache_n_retrievals_nomem);
    else if (ret == -ERESTARTSYS)
        fscache_stat(&fscache_n_retrievals_intr);
    else if (ret == -ENODATA)
        fscache_stat(&fscache_n_retrievals_nodata);
    else if (ret < 0)
        fscache_stat(&fscache_n_retrievals_nobufs);
    else
        fscache_stat(&fscache_n_retrievals_ok);

    fscache_put_retrieval(op);
    _leave(" = %d", ret);
    return ret;

nobufs_unlock:
    spin_unlock(&cookie->lock);
    kfree(op);
nobufs:
    fscache_stat(&fscache_n_retrievals_nobufs);
    _leave(" = -ENOBUFS");
    return -ENOBUFS;
}
EXPORT_SYMBOL(__fscache_read_or_alloc_page);

/*
 * read a list of page from the cache or allocate a block in which to store
 * them
 * - we return:
 *   -ENOMEM    - out of memory, some pages may be being read
 *   -ERESTARTSYS - interrupted, some pages may be being read
 *   -ENOBUFS   - no backing object or space available in which to cache any
 *                pages not being read
 *   -ENODATA   - no data available in the backing object for some or all of
 *                the pages
 *   0      - dispatched a read on all pages
 *
 * end_io_func() will be called for each page read from the cache as it is
 * finishes being read
 *
 * any pages for which a read is dispatched will be removed from pages and
 * nr_pages
 */
int __fscache_read_or_alloc_pages(struct fscache_cookie *cookie,
                  struct address_space *mapping,
                  struct list_head *pages,
                  unsigned *nr_pages,
                  fscache_rw_complete_t end_io_func,
                  void *context,
                  gfp_t gfp)
{
    struct fscache_retrieval *op;
    struct fscache_object *object;
    int ret;

    _enter("%p,,%d,,,", cookie, *nr_pages);

    fscache_stat(&fscache_n_retrievals);

    if (hlist_empty(&cookie->backing_objects))
        goto nobufs;

    ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
    ASSERTCMP(*nr_pages, >, 0);
    ASSERT(!list_empty(pages));

    if (fscache_wait_for_deferred_lookup(cookie) < 0)
        return -ERESTARTSYS;

    op = fscache_alloc_retrieval(mapping, end_io_func, context);
    if (!op)
        return -ENOMEM;

    spin_lock(&cookie->lock);

    if (hlist_empty(&cookie->backing_objects))
        goto nobufs_unlock;
    object = hlist_entry(cookie->backing_objects.first,
                 struct fscache_object, cookie_link);

    atomic_inc(&object->n_reads);
    set_bit(FSCACHE_OP_DEC_READ_CNT, &op->op.flags);

    if (fscache_submit_op(object, &op->op) < 0)
        goto nobufs_unlock;
    spin_unlock(&cookie->lock);

    fscache_stat(&fscache_n_retrieval_ops);

    /* pin the netfs read context in case we need to do the actual netfs
     * read because we've encountered a cache read failure */
    fscache_get_context(object->cookie, op->context);

    /* we wait for the operation to become active, and then process it
     * *here*, in this thread, and not in the thread pool */
    ret = fscache_wait_for_retrieval_activation(
        object, op,
        __fscache_stat(&fscache_n_retrieval_op_waits),
        __fscache_stat(&fscache_n_retrievals_object_dead));
    if (ret < 0)
        goto error;

    /* ask the cache to honour the operation */
    if (test_bit(FSCACHE_COOKIE_NO_DATA_YET, &object->cookie->flags)) {
        fscache_stat(&fscache_n_cop_allocate_pages);
        ret = object->cache->ops->allocate_pages(
            op, pages, nr_pages, gfp);
        fscache_stat_d(&fscache_n_cop_allocate_pages);
    } else {
        fscache_stat(&fscache_n_cop_read_or_alloc_pages);
        ret = object->cache->ops->read_or_alloc_pages(
            op, pages, nr_pages, gfp);
        fscache_stat_d(&fscache_n_cop_read_or_alloc_pages);
    }

error:
    if (ret == -ENOMEM)
        fscache_stat(&fscache_n_retrievals_nomem);
    else if (ret == -ERESTARTSYS)
        fscache_stat(&fscache_n_retrievals_intr);
    else if (ret == -ENODATA)
        fscache_stat(&fscache_n_retrievals_nodata);
    else if (ret < 0)
        fscache_stat(&fscache_n_retrievals_nobufs);
    else
        fscache_stat(&fscache_n_retrievals_ok);

    fscache_put_retrieval(op);
    _leave(" = %d", ret);
    return ret;

nobufs_unlock:
    spin_unlock(&cookie->lock);
    kfree(op);
nobufs:
    fscache_stat(&fscache_n_retrievals_nobufs);
    _leave(" = -ENOBUFS");
    return -ENOBUFS;
}
EXPORT_SYMBOL(__fscache_read_or_alloc_pages);

/*
 * allocate a block in the cache on which to store a page
 * - we return:
 *   -ENOMEM    - out of memory, nothing done
 *   -ERESTARTSYS - interrupted
 *   -ENOBUFS   - no backing object available in which to cache the block
 *   0      - block allocated
 */
int __fscache_alloc_page(struct fscache_cookie *cookie,
             struct page *page,
             gfp_t gfp)
{
    struct fscache_retrieval *op;
    struct fscache_object *object;
    int ret;

    _enter("%p,%p,,,", cookie, page);

    fscache_stat(&fscache_n_allocs);

    if (hlist_empty(&cookie->backing_objects))
        goto nobufs;

    ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
    ASSERTCMP(page, !=, NULL);

    if (fscache_wait_for_deferred_lookup(cookie) < 0)
        return -ERESTARTSYS;

    op = fscache_alloc_retrieval(page->mapping, NULL, NULL);
    if (!op)
        return -ENOMEM;

    spin_lock(&cookie->lock);

    if (hlist_empty(&cookie->backing_objects))
        goto nobufs_unlock;
    object = hlist_entry(cookie->backing_objects.first,
                 struct fscache_object, cookie_link);

    if (fscache_submit_op(object, &op->op) < 0)
        goto nobufs_unlock;
    spin_unlock(&cookie->lock);

    fscache_stat(&fscache_n_alloc_ops);

    ret = fscache_wait_for_retrieval_activation(
        object, op,
        __fscache_stat(&fscache_n_alloc_op_waits),
        __fscache_stat(&fscache_n_allocs_object_dead));
    if (ret < 0)
        goto error;

    /* ask the cache to honour the operation */
    fscache_stat(&fscache_n_cop_allocate_page);
    ret = object->cache->ops->allocate_page(op, page, gfp);
    fscache_stat_d(&fscache_n_cop_allocate_page);

error:
    if (ret == -ERESTARTSYS)
        fscache_stat(&fscache_n_allocs_intr);
    else if (ret < 0)
        fscache_stat(&fscache_n_allocs_nobufs);
    else
        fscache_stat(&fscache_n_allocs_ok);

    fscache_put_retrieval(op);
    _leave(" = %d", ret);
    return ret;

nobufs_unlock:
    spin_unlock(&cookie->lock);
    kfree(op);
nobufs:
    fscache_stat(&fscache_n_allocs_nobufs);
    _leave(" = -ENOBUFS");
    return -ENOBUFS;
}
EXPORT_SYMBOL(__fscache_alloc_page);

/*
 * release a write op reference
 */
static void fscache_release_write_op(struct fscache_operation *_op)
{
    _enter("{OP%x}", _op->debug_id);
}

/*
 * perform the background storage of a page into the cache
 */
static void fscache_write_op(struct fscache_operation *_op)
{
    struct fscache_storage *op =
        container_of(_op, struct fscache_storage, op);
    struct fscache_object *object = op->op.object;
    struct fscache_cookie *cookie;
    struct page *page;
    unsigned n;
    void *results[1];
    int ret;

    _enter("{OP%x,%d}", op->op.debug_id, atomic_read(&op->op.usage));

    spin_lock(&object->lock);
    cookie = object->cookie;

    if (!fscache_object_is_active(object) || !cookie) {
        spin_unlock(&object->lock);
        _leave("");
        return;
    }

    spin_lock(&cookie->stores_lock);

    fscache_stat(&fscache_n_store_calls);

    /* find a page to store */
    page = NULL;
    n = radix_tree_gang_lookup_tag(&cookie->stores, results, 0, 1,
                       FSCACHE_COOKIE_PENDING_TAG);
    if (n != 1)
        goto superseded;
    page = results[0];
    _debug("gang %d [%lx]", n, page->index);
    if (page->index > op->store_limit) {
        fscache_stat(&fscache_n_store_pages_over_limit);
        goto superseded;
    }

    radix_tree_tag_set(&cookie->stores, page->index,
               FSCACHE_COOKIE_STORING_TAG);
    radix_tree_tag_clear(&cookie->stores, page->index,
                 FSCACHE_COOKIE_PENDING_TAG);

    spin_unlock(&cookie->stores_lock);
    spin_unlock(&object->lock);

    fscache_stat(&fscache_n_store_pages);
    fscache_stat(&fscache_n_cop_write_page);
    ret = object->cache->ops->write_page(op, page);
    fscache_stat_d(&fscache_n_cop_write_page);
    fscache_end_page_write(object, page);
    if (ret < 0) {
        fscache_abort_object(object);
    } else {
        fscache_enqueue_operation(&op->op);
    }

    _leave("");
    return;

superseded:
    /* this writer is going away and there aren't any more things to
     * write */
    _debug("cease");
    spin_unlock(&cookie->stores_lock);
    clear_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags);
    spin_unlock(&object->lock);
    _leave("");
}

/*
 * request a page be stored in the cache
 * - returns:
 *   -ENOMEM    - out of memory, nothing done
 *   -ENOBUFS   - no backing object available in which to cache the page
 *   0      - dispatched a write - it'll call end_io_func() when finished
 *
 * if the cookie still has a backing object at this point, that object can be
 * in one of a few states with respect to storage processing:
 *
 *  (1) negative lookup, object not yet created (FSCACHE_COOKIE_CREATING is
 *      set)
 *
 *  (a) no writes yet (set FSCACHE_COOKIE_PENDING_FILL and queue deferred
 *      fill op)
 *
 *  (b) writes deferred till post-creation (mark page for writing and
 *      return immediately)
 *
 *  (2) negative lookup, object created, initial fill being made from netfs
 *      (FSCACHE_COOKIE_INITIAL_FILL is set)
 *
 *  (a) fill point not yet reached this page (mark page for writing and
 *          return)
 *
 *  (b) fill point passed this page (queue op to store this page)
 *
 *  (3) object extant (queue op to store this page)
 *
 * any other state is invalid
 */
int __fscache_write_page(struct fscache_cookie *cookie,
             struct page *page,
             gfp_t gfp)
{
    struct fscache_storage *op;
    struct fscache_object *object;
    int ret;

    _enter("%p,%x,", cookie, (u32) page->flags);

    ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
    ASSERT(PageFsCache(page));

    fscache_stat(&fscache_n_stores);

    op = kzalloc(sizeof(*op), GFP_NOIO);
    if (!op)
        goto nomem;

    fscache_operation_init(&op->op, fscache_write_op,
                   fscache_release_write_op);
    op->op.flags = FSCACHE_OP_ASYNC | (1 << FSCACHE_OP_WAITING);

    ret = radix_tree_preload(gfp & ~__GFP_HIGHMEM);
    if (ret < 0)
        goto nomem_free;

    ret = -ENOBUFS;
    spin_lock(&cookie->lock);

    if (hlist_empty(&cookie->backing_objects))
        goto nobufs;
    object = hlist_entry(cookie->backing_objects.first,
                 struct fscache_object, cookie_link);
    if (test_bit(FSCACHE_IOERROR, &object->cache->flags))
        goto nobufs;

    /* add the page to the pending-storage radix tree on the backing
     * object */
    spin_lock(&object->lock);
    spin_lock(&cookie->stores_lock);

    _debug("store limit %llx", (unsigned long long) object->store_limit);

    ret = radix_tree_insert(&cookie->stores, page->index, page);
    if (ret < 0) {
        if (ret == -EEXIST)
            goto already_queued;
        _debug("insert failed %d", ret);
        goto nobufs_unlock_obj;
    }

    radix_tree_tag_set(&cookie->stores, page->index,
               FSCACHE_COOKIE_PENDING_TAG);
    page_cache_get(page);

    /* we only want one writer at a time, but we do need to queue new
     * writers after exclusive ops */
    if (test_and_set_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags))
        goto already_pending;

    spin_unlock(&cookie->stores_lock);
    spin_unlock(&object->lock);

    op->op.debug_id = atomic_inc_return(&fscache_op_debug_id);
    op->store_limit = object->store_limit;

    if (fscache_submit_op(object, &op->op) < 0)
        goto submit_failed;

    spin_unlock(&cookie->lock);
    radix_tree_preload_end();
    fscache_stat(&fscache_n_store_ops);
    fscache_stat(&fscache_n_stores_ok);

    /* the work queue now carries its own ref on the object */
    fscache_put_operation(&op->op);
    _leave(" = 0");
    return 0;

already_queued:
    fscache_stat(&fscache_n_stores_again);
already_pending:
    spin_unlock(&cookie->stores_lock);
    spin_unlock(&object->lock);
    spin_unlock(&cookie->lock);
    radix_tree_preload_end();
    kfree(op);
    fscache_stat(&fscache_n_stores_ok);
    _leave(" = 0");
    return 0;

submit_failed:
    spin_lock(&cookie->stores_lock);
    radix_tree_delete(&cookie->stores, page->index);
    spin_unlock(&cookie->stores_lock);
    page_cache_release(page);
    ret = -ENOBUFS;
    goto nobufs;

nobufs_unlock_obj:
    spin_unlock(&cookie->stores_lock);
    spin_unlock(&object->lock);
nobufs:
    spin_unlock(&cookie->lock);
    radix_tree_preload_end();
    kfree(op);
    fscache_stat(&fscache_n_stores_nobufs);
    _leave(" = -ENOBUFS");
    return -ENOBUFS;

nomem_free:
    kfree(op);
nomem:
    fscache_stat(&fscache_n_stores_oom);
    _leave(" = -ENOMEM");
    return -ENOMEM;
}
EXPORT_SYMBOL(__fscache_write_page);

/*
 * remove a page from the cache
 */
void __fscache_uncache_page(struct fscache_cookie *cookie, struct page *page)
{
    struct fscache_object *object;

    _enter(",%p", page);

    ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
    ASSERTCMP(page, !=, NULL);

    fscache_stat(&fscache_n_uncaches);

    /* cache withdrawal may beat us to it */
    if (!PageFsCache(page))
        goto done;

    /* get the object */
    spin_lock(&cookie->lock);

    if (hlist_empty(&cookie->backing_objects)) {
        ClearPageFsCache(page);
        goto done_unlock;
    }

    object = hlist_entry(cookie->backing_objects.first,
                 struct fscache_object, cookie_link);

    /* there might now be stuff on disk we could read */
    clear_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);

    /* only invoke the cache backend if we managed to mark the page
     * uncached here; this deals with synchronisation vs withdrawal */
    if (TestClearPageFsCache(page) &&
        object->cache->ops->uncache_page) {
        /* the cache backend releases the cookie lock */
        fscache_stat(&fscache_n_cop_uncache_page);
        object->cache->ops->uncache_page(object, page);
        fscache_stat_d(&fscache_n_cop_uncache_page);
        goto done;
    }

done_unlock:
    spin_unlock(&cookie->lock);
done:
    _leave("");
}
EXPORT_SYMBOL(__fscache_uncache_page);

void fscache_mark_pages_cached(struct fscache_retrieval *op,
                   struct pagevec *pagevec)
{
    struct fscache_cookie *cookie = op->op.object->cookie;
    unsigned long loop;

#ifdef CONFIG_FSCACHE_STATS
    atomic_add(pagevec->nr, &fscache_n_marks);
#endif

    for (loop = 0; loop < pagevec->nr; loop++) {
        struct page *page = pagevec->pages[loop];

        _debug("- mark %p{%lx}", page, page->index);
        if (TestSetPageFsCache(page)) {
            static bool once_only;
            if (!once_only) {
                once_only = true;
                printk(KERN_WARNING "FS-Cache:"
                       " Cookie type %s marked page %lx"
                       " multiple times\n",
                       cookie->def->name, page->index);
            }
        }
    }

    if (cookie->def->mark_pages_cached)
        cookie->def->mark_pages_cached(cookie->netfs_data,
                           op->mapping, pagevec);
    pagevec_reinit(pagevec);
}
EXPORT_SYMBOL(fscache_mark_pages_cached);

/*
 * Uncache all the pages in an inode that are marked PG_fscache, assuming them
 * to be associated with the given cookie.
 */
void __fscache_uncache_all_inode_pages(struct fscache_cookie *cookie,
                       struct inode *inode)
{
    struct address_space *mapping = inode->i_mapping;
    struct pagevec pvec;
    pgoff_t next;
    int i;

    _enter("%p,%p", cookie, inode);

    if (!mapping || mapping->nrpages == 0) {
        _leave(" [no pages]");
        return;
    }

    pagevec_init(&pvec, 0);
    next = 0;
    do {
        if (!pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE))
            break;
        for (i = 0; i < pagevec_count(&pvec); i++) {
            struct page *page = pvec.pages[i];
            next = page->index;
            if (PageFsCache(page)) {
                __fscache_wait_on_page_write(cookie, page);
                __fscache_uncache_page(cookie, page);
            }
        }
        pagevec_release(&pvec);
        cond_resched();
    } while (++next);

    _leave("");
}
EXPORT_SYMBOL(__fscache_uncache_all_inode_pages);