interface.c

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/* FS-Cache interface to CacheFiles
 *
 * Copyright (C) 2007 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 Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#include <linux/slab.h>
#include <linux/mount.h>
#include "internal.h"

#define list_to_page(head) (list_entry((head)->prev, struct page, lru))

struct cachefiles_lookup_data {
    struct cachefiles_xattr *auxdata;   /* auxiliary data */
    char            *key;       /* key path */
};

static int cachefiles_attr_changed(struct fscache_object *_object);

/*
 * allocate an object record for a cookie lookup and prepare the lookup data
 */
static struct fscache_object *cachefiles_alloc_object(
    struct fscache_cache *_cache,
    struct fscache_cookie *cookie)
{
    struct cachefiles_lookup_data *lookup_data;
    struct cachefiles_object *object;
    struct cachefiles_cache *cache;
    struct cachefiles_xattr *auxdata;
    unsigned keylen, auxlen;
    void *buffer;
    char *key;

    cache = container_of(_cache, struct cachefiles_cache, cache);

    _enter("{%s},%p,", cache->cache.identifier, cookie);

    lookup_data = kmalloc(sizeof(*lookup_data), GFP_KERNEL);
    if (!lookup_data)
        goto nomem_lookup_data;

    /* create a new object record and a temporary leaf image */
    object = kmem_cache_alloc(cachefiles_object_jar, GFP_KERNEL);
    if (!object)
        goto nomem_object;

    ASSERTCMP(object->backer, ==, NULL);

    BUG_ON(test_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags));
    atomic_set(&object->usage, 1);

    fscache_object_init(&object->fscache, cookie, &cache->cache);

    object->type = cookie->def->type;

    /* get hold of the raw key
     * - stick the length on the front and leave space on the back for the
     *   encoder
     */
    buffer = kmalloc((2 + 512) + 3, GFP_KERNEL);
    if (!buffer)
        goto nomem_buffer;

    keylen = cookie->def->get_key(cookie->netfs_data, buffer + 2, 512);
    ASSERTCMP(keylen, <, 512);

    *(uint16_t *)buffer = keylen;
    ((char *)buffer)[keylen + 2] = 0;
    ((char *)buffer)[keylen + 3] = 0;
    ((char *)buffer)[keylen + 4] = 0;

    /* turn the raw key into something that can work with as a filename */
    key = cachefiles_cook_key(buffer, keylen + 2, object->type);
    if (!key)
        goto nomem_key;

    /* get hold of the auxiliary data and prepend the object type */
    auxdata = buffer;
    auxlen = 0;
    if (cookie->def->get_aux) {
        auxlen = cookie->def->get_aux(cookie->netfs_data,
                          auxdata->data, 511);
        ASSERTCMP(auxlen, <, 511);
    }

    auxdata->len = auxlen + 1;
    auxdata->type = cookie->def->type;

    lookup_data->auxdata = auxdata;
    lookup_data->key = key;
    object->lookup_data = lookup_data;

    _leave(" = %p [%p]", &object->fscache, lookup_data);
    return &object->fscache;

nomem_key:
    kfree(buffer);
nomem_buffer:
    BUG_ON(test_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags));
    kmem_cache_free(cachefiles_object_jar, object);
    fscache_object_destroyed(&cache->cache);
nomem_object:
    kfree(lookup_data);
nomem_lookup_data:
    _leave(" = -ENOMEM");
    return ERR_PTR(-ENOMEM);
}

/*
 * attempt to look up the nominated node in this cache
 * - return -ETIMEDOUT to be scheduled again
 */
static int cachefiles_lookup_object(struct fscache_object *_object)
{
    struct cachefiles_lookup_data *lookup_data;
    struct cachefiles_object *parent, *object;
    struct cachefiles_cache *cache;
    const struct cred *saved_cred;
    int ret;

    _enter("{OBJ%x}", _object->debug_id);

    cache = container_of(_object->cache, struct cachefiles_cache, cache);
    parent = container_of(_object->parent,
                  struct cachefiles_object, fscache);
    object = container_of(_object, struct cachefiles_object, fscache);
    lookup_data = object->lookup_data;

    ASSERTCMP(lookup_data, !=, NULL);

    /* look up the key, creating any missing bits */
    cachefiles_begin_secure(cache, &saved_cred);
    ret = cachefiles_walk_to_object(parent, object,
                    lookup_data->key,
                    lookup_data->auxdata);
    cachefiles_end_secure(cache, saved_cred);

    /* polish off by setting the attributes of non-index files */
    if (ret == 0 &&
        object->fscache.cookie->def->type != FSCACHE_COOKIE_TYPE_INDEX)
        cachefiles_attr_changed(&object->fscache);

    if (ret < 0 && ret != -ETIMEDOUT) {
        if (ret != -ENOBUFS)
            printk(KERN_WARNING
                   "CacheFiles: Lookup failed error %d\n", ret);
        fscache_object_lookup_error(&object->fscache);
    }

    _leave(" [%d]", ret);
    return ret;
}

/*
 * indication of lookup completion
 */
static void cachefiles_lookup_complete(struct fscache_object *_object)
{
    struct cachefiles_object *object;

    object = container_of(_object, struct cachefiles_object, fscache);

    _enter("{OBJ%x,%p}", object->fscache.debug_id, object->lookup_data);

    if (object->lookup_data) {
        kfree(object->lookup_data->key);
        kfree(object->lookup_data->auxdata);
        kfree(object->lookup_data);
        object->lookup_data = NULL;
    }
}

/*
 * increment the usage count on an inode object (may fail if unmounting)
 */
static
struct fscache_object *cachefiles_grab_object(struct fscache_object *_object)
{
    struct cachefiles_object *object =
        container_of(_object, struct cachefiles_object, fscache);

    _enter("{OBJ%x,%d}", _object->debug_id, atomic_read(&object->usage));

#ifdef CACHEFILES_DEBUG_SLAB
    ASSERT((atomic_read(&object->usage) & 0xffff0000) != 0x6b6b0000);
#endif

    atomic_inc(&object->usage);
    return &object->fscache;
}

/*
 * update the auxiliary data for an object object on disk
 */
static void cachefiles_update_object(struct fscache_object *_object)
{
    struct cachefiles_object *object;
    struct cachefiles_xattr *auxdata;
    struct cachefiles_cache *cache;
    struct fscache_cookie *cookie;
    const struct cred *saved_cred;
    unsigned auxlen;

    _enter("{OBJ%x}", _object->debug_id);

    object = container_of(_object, struct cachefiles_object, fscache);
    cache = container_of(object->fscache.cache, struct cachefiles_cache,
                 cache);
    cookie = object->fscache.cookie;

    if (!cookie->def->get_aux) {
        _leave(" [no aux]");
        return;
    }

    auxdata = kmalloc(2 + 512 + 3, GFP_KERNEL);
    if (!auxdata) {
        _leave(" [nomem]");
        return;
    }

    auxlen = cookie->def->get_aux(cookie->netfs_data, auxdata->data, 511);
    ASSERTCMP(auxlen, <, 511);

    auxdata->len = auxlen + 1;
    auxdata->type = cookie->def->type;

    cachefiles_begin_secure(cache, &saved_cred);
    cachefiles_update_object_xattr(object, auxdata);
    cachefiles_end_secure(cache, saved_cred);
    kfree(auxdata);
    _leave("");
}

/*
 * discard the resources pinned by an object and effect retirement if
 * requested
 */
static void cachefiles_drop_object(struct fscache_object *_object)
{
    struct cachefiles_object *object;
    struct cachefiles_cache *cache;
    const struct cred *saved_cred;

    ASSERT(_object);

    object = container_of(_object, struct cachefiles_object, fscache);

    _enter("{OBJ%x,%d}",
           object->fscache.debug_id, atomic_read(&object->usage));

    cache = container_of(object->fscache.cache,
                 struct cachefiles_cache, cache);

#ifdef CACHEFILES_DEBUG_SLAB
    ASSERT((atomic_read(&object->usage) & 0xffff0000) != 0x6b6b0000);
#endif

    /* delete retired objects */
    if (object->fscache.state == FSCACHE_OBJECT_RECYCLING &&
        _object != cache->cache.fsdef
        ) {
        _debug("- retire object OBJ%x", object->fscache.debug_id);
        cachefiles_begin_secure(cache, &saved_cred);
        cachefiles_delete_object(cache, object);
        cachefiles_end_secure(cache, saved_cred);
    }

    /* close the filesystem stuff attached to the object */
    if (object->backer != object->dentry)
        dput(object->backer);
    object->backer = NULL;

    /* note that the object is now inactive */
    if (test_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags)) {
        write_lock(&cache->active_lock);
        if (!test_and_clear_bit(CACHEFILES_OBJECT_ACTIVE,
                    &object->flags))
            BUG();
        rb_erase(&object->active_node, &cache->active_nodes);
        wake_up_bit(&object->flags, CACHEFILES_OBJECT_ACTIVE);
        write_unlock(&cache->active_lock);
    }

    dput(object->dentry);
    object->dentry = NULL;

    _leave("");
}

/*
 * dispose of a reference to an object
 */
static void cachefiles_put_object(struct fscache_object *_object)
{
    struct cachefiles_object *object;
    struct fscache_cache *cache;

    ASSERT(_object);

    object = container_of(_object, struct cachefiles_object, fscache);

    _enter("{OBJ%x,%d}",
           object->fscache.debug_id, atomic_read(&object->usage));

#ifdef CACHEFILES_DEBUG_SLAB
    ASSERT((atomic_read(&object->usage) & 0xffff0000) != 0x6b6b0000);
#endif

    ASSERTIFCMP(object->fscache.parent,
            object->fscache.parent->n_children, >, 0);

    if (atomic_dec_and_test(&object->usage)) {
        _debug("- kill object OBJ%x", object->fscache.debug_id);

        ASSERT(!test_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags));
        ASSERTCMP(object->fscache.parent, ==, NULL);
        ASSERTCMP(object->backer, ==, NULL);
        ASSERTCMP(object->dentry, ==, NULL);
        ASSERTCMP(object->fscache.n_ops, ==, 0);
        ASSERTCMP(object->fscache.n_children, ==, 0);

        if (object->lookup_data) {
            kfree(object->lookup_data->key);
            kfree(object->lookup_data->auxdata);
            kfree(object->lookup_data);
            object->lookup_data = NULL;
        }

        cache = object->fscache.cache;
        fscache_object_destroy(&object->fscache);
        kmem_cache_free(cachefiles_object_jar, object);
        fscache_object_destroyed(cache);
    }

    _leave("");
}

/*
 * sync a cache
 */
static void cachefiles_sync_cache(struct fscache_cache *_cache)
{
    struct cachefiles_cache *cache;
    const struct cred *saved_cred;
    int ret;

    _enter("%p", _cache);

    cache = container_of(_cache, struct cachefiles_cache, cache);

    /* make sure all pages pinned by operations on behalf of the netfs are
     * written to disc */
    cachefiles_begin_secure(cache, &saved_cred);
    down_read(&cache->mnt->mnt_sb->s_umount);
    ret = sync_filesystem(cache->mnt->mnt_sb);
    up_read(&cache->mnt->mnt_sb->s_umount);
    cachefiles_end_secure(cache, saved_cred);

    if (ret == -EIO)
        cachefiles_io_error(cache,
                    "Attempt to sync backing fs superblock"
                    " returned error %d",
                    ret);
}

/*
 * notification the attributes on an object have changed
 * - called with reads/writes excluded by FS-Cache
 */
static int cachefiles_attr_changed(struct fscache_object *_object)
{
    struct cachefiles_object *object;
    struct cachefiles_cache *cache;
    const struct cred *saved_cred;
    struct iattr newattrs;
    uint64_t ni_size;
    loff_t oi_size;
    int ret;

    _object->cookie->def->get_attr(_object->cookie->netfs_data, &ni_size);

    _enter("{OBJ%x},[%llu]",
           _object->debug_id, (unsigned long long) ni_size);

    object = container_of(_object, struct cachefiles_object, fscache);
    cache = container_of(object->fscache.cache,
                 struct cachefiles_cache, cache);

    if (ni_size == object->i_size)
        return 0;

    if (!object->backer)
        return -ENOBUFS;

    ASSERT(S_ISREG(object->backer->d_inode->i_mode));

    fscache_set_store_limit(&object->fscache, ni_size);

    oi_size = i_size_read(object->backer->d_inode);
    if (oi_size == ni_size)
        return 0;

    cachefiles_begin_secure(cache, &saved_cred);
    mutex_lock(&object->backer->d_inode->i_mutex);

    /* if there's an extension to a partial page at the end of the backing
     * file, we need to discard the partial page so that we pick up new
     * data after it */
    if (oi_size & ~PAGE_MASK && ni_size > oi_size) {
        _debug("discard tail %llx", oi_size);
        newattrs.ia_valid = ATTR_SIZE;
        newattrs.ia_size = oi_size & PAGE_MASK;
        ret = notify_change(object->backer, &newattrs);
        if (ret < 0)
            goto truncate_failed;
    }

    newattrs.ia_valid = ATTR_SIZE;
    newattrs.ia_size = ni_size;
    ret = notify_change(object->backer, &newattrs);

truncate_failed:
    mutex_unlock(&object->backer->d_inode->i_mutex);
    cachefiles_end_secure(cache, saved_cred);

    if (ret == -EIO) {
        fscache_set_store_limit(&object->fscache, 0);
        cachefiles_io_error_obj(object, "Size set failed");
        ret = -ENOBUFS;
    }

    _leave(" = %d", ret);
    return ret;
}

/*
 * dissociate a cache from all the pages it was backing
 */
static void cachefiles_dissociate_pages(struct fscache_cache *cache)
{
    _enter("");
}

const struct fscache_cache_ops cachefiles_cache_ops = {
    .name           = "cachefiles",
    .alloc_object       = cachefiles_alloc_object,
    .lookup_object      = cachefiles_lookup_object,
    .lookup_complete    = cachefiles_lookup_complete,
    .grab_object        = cachefiles_grab_object,
    .update_object      = cachefiles_update_object,
    .drop_object        = cachefiles_drop_object,
    .put_object     = cachefiles_put_object,
    .sync_cache     = cachefiles_sync_cache,
    .attr_changed       = cachefiles_attr_changed,
    .read_or_alloc_page = cachefiles_read_or_alloc_page,
    .read_or_alloc_pages    = cachefiles_read_or_alloc_pages,
    .allocate_page      = cachefiles_allocate_page,
    .allocate_pages     = cachefiles_allocate_pages,
    .write_page     = cachefiles_write_page,
    .uncache_page       = cachefiles_uncache_page,
    .dissociate_pages   = cachefiles_dissociate_pages,
};