namei.c

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/* CacheFiles path walking and related routines
 *
 * 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/module.h>
#include <linux/sched.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/fsnotify.h>
#include <linux/quotaops.h>
#include <linux/xattr.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/security.h>
#include <linux/slab.h>
#include "internal.h"

#define CACHEFILES_KEYBUF_SIZE 512

/*
 * dump debugging info about an object
 */
static noinline
void __cachefiles_printk_object(struct cachefiles_object *object,
                const char *prefix,
                u8 *keybuf)
{
    struct fscache_cookie *cookie;
    unsigned keylen, loop;

    printk(KERN_ERR "%sobject: OBJ%x\n",
           prefix, object->fscache.debug_id);
    printk(KERN_ERR "%sobjstate=%s fl=%lx wbusy=%x ev=%lx[%lx]\n",
           prefix, fscache_object_states[object->fscache.state],
           object->fscache.flags, work_busy(&object->fscache.work),
           object->fscache.events,
           object->fscache.event_mask & FSCACHE_OBJECT_EVENTS_MASK);
    printk(KERN_ERR "%sops=%u inp=%u exc=%u\n",
           prefix, object->fscache.n_ops, object->fscache.n_in_progress,
           object->fscache.n_exclusive);
    printk(KERN_ERR "%sparent=%p\n",
           prefix, object->fscache.parent);

    spin_lock(&object->fscache.lock);
    cookie = object->fscache.cookie;
    if (cookie) {
        printk(KERN_ERR "%scookie=%p [pr=%p nd=%p fl=%lx]\n",
               prefix,
               object->fscache.cookie,
               object->fscache.cookie->parent,
               object->fscache.cookie->netfs_data,
               object->fscache.cookie->flags);
        if (keybuf)
            keylen = cookie->def->get_key(cookie->netfs_data, keybuf,
                              CACHEFILES_KEYBUF_SIZE);
        else
            keylen = 0;
    } else {
        printk(KERN_ERR "%scookie=NULL\n", prefix);
        keylen = 0;
    }
    spin_unlock(&object->fscache.lock);

    if (keylen) {
        printk(KERN_ERR "%skey=[%u] '", prefix, keylen);
        for (loop = 0; loop < keylen; loop++)
            printk("%02x", keybuf[loop]);
        printk("'\n");
    }
}

/*
 * dump debugging info about a pair of objects
 */
static noinline void cachefiles_printk_object(struct cachefiles_object *object,
                          struct cachefiles_object *xobject)
{
    u8 *keybuf;

    keybuf = kmalloc(CACHEFILES_KEYBUF_SIZE, GFP_NOIO);
    if (object)
        __cachefiles_printk_object(object, "", keybuf);
    if (xobject)
        __cachefiles_printk_object(xobject, "x", keybuf);
    kfree(keybuf);
}

/*
 * mark the owner of a dentry, if there is one, to indicate that that dentry
 * has been preemptively deleted
 * - the caller must hold the i_mutex on the dentry's parent as required to
 *   call vfs_unlink(), vfs_rmdir() or vfs_rename()
 */
static void cachefiles_mark_object_buried(struct cachefiles_cache *cache,
                      struct dentry *dentry)
{
    struct cachefiles_object *object;
    struct rb_node *p;

    _enter(",'%*.*s'",
           dentry->d_name.len, dentry->d_name.len, dentry->d_name.name);

    write_lock(&cache->active_lock);

    p = cache->active_nodes.rb_node;
    while (p) {
        object = rb_entry(p, struct cachefiles_object, active_node);
        if (object->dentry > dentry)
            p = p->rb_left;
        else if (object->dentry < dentry)
            p = p->rb_right;
        else
            goto found_dentry;
    }

    write_unlock(&cache->active_lock);
    _leave(" [no owner]");
    return;

    /* found the dentry for  */
found_dentry:
    kdebug("preemptive burial: OBJ%x [%s] %p",
           object->fscache.debug_id,
           fscache_object_states[object->fscache.state],
           dentry);

    if (object->fscache.state < FSCACHE_OBJECT_DYING) {
        printk(KERN_ERR "\n");
        printk(KERN_ERR "CacheFiles: Error:"
               " Can't preemptively bury live object\n");
        cachefiles_printk_object(object, NULL);
    } else if (test_and_set_bit(CACHEFILES_OBJECT_BURIED, &object->flags)) {
        printk(KERN_ERR "CacheFiles: Error:"
               " Object already preemptively buried\n");
    }

    write_unlock(&cache->active_lock);
    _leave(" [owner marked]");
}

/*
 * record the fact that an object is now active
 */
static int cachefiles_mark_object_active(struct cachefiles_cache *cache,
                     struct cachefiles_object *object)
{
    struct cachefiles_object *xobject;
    struct rb_node **_p, *_parent = NULL;
    struct dentry *dentry;

    _enter(",%p", object);

try_again:
    write_lock(&cache->active_lock);

    if (test_and_set_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags)) {
        printk(KERN_ERR "CacheFiles: Error: Object already active\n");
        cachefiles_printk_object(object, NULL);
        BUG();
    }

    dentry = object->dentry;
    _p = &cache->active_nodes.rb_node;
    while (*_p) {
        _parent = *_p;
        xobject = rb_entry(_parent,
                   struct cachefiles_object, active_node);

        ASSERT(xobject != object);

        if (xobject->dentry > dentry)
            _p = &(*_p)->rb_left;
        else if (xobject->dentry < dentry)
            _p = &(*_p)->rb_right;
        else
            goto wait_for_old_object;
    }

    rb_link_node(&object->active_node, _parent, _p);
    rb_insert_color(&object->active_node, &cache->active_nodes);

    write_unlock(&cache->active_lock);
    _leave(" = 0");
    return 0;

    /* an old object from a previous incarnation is hogging the slot - we
     * need to wait for it to be destroyed */
wait_for_old_object:
    if (xobject->fscache.state < FSCACHE_OBJECT_DYING) {
        printk(KERN_ERR "\n");
        printk(KERN_ERR "CacheFiles: Error:"
               " Unexpected object collision\n");
        cachefiles_printk_object(object, xobject);
        BUG();
    }
    atomic_inc(&xobject->usage);
    write_unlock(&cache->active_lock);

    if (test_bit(CACHEFILES_OBJECT_ACTIVE, &xobject->flags)) {
        wait_queue_head_t *wq;

        signed long timeout = 60 * HZ;
        wait_queue_t wait;
        bool requeue;

        /* if the object we're waiting for is queued for processing,
         * then just put ourselves on the queue behind it */
        if (work_pending(&xobject->fscache.work)) {
            _debug("queue OBJ%x behind OBJ%x immediately",
                   object->fscache.debug_id,
                   xobject->fscache.debug_id);
            goto requeue;
        }

        /* otherwise we sleep until either the object we're waiting for
         * is done, or the fscache_object is congested */
        wq = bit_waitqueue(&xobject->flags, CACHEFILES_OBJECT_ACTIVE);
        init_wait(&wait);
        requeue = false;
        do {
            prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE);
            if (!test_bit(CACHEFILES_OBJECT_ACTIVE, &xobject->flags))
                break;

            requeue = fscache_object_sleep_till_congested(&timeout);
        } while (timeout > 0 && !requeue);
        finish_wait(wq, &wait);

        if (requeue &&
            test_bit(CACHEFILES_OBJECT_ACTIVE, &xobject->flags)) {
            _debug("queue OBJ%x behind OBJ%x after wait",
                   object->fscache.debug_id,
                   xobject->fscache.debug_id);
            goto requeue;
        }

        if (timeout <= 0) {
            printk(KERN_ERR "\n");
            printk(KERN_ERR "CacheFiles: Error: Overlong"
                   " wait for old active object to go away\n");
            cachefiles_printk_object(object, xobject);
            goto requeue;
        }
    }

    ASSERT(!test_bit(CACHEFILES_OBJECT_ACTIVE, &xobject->flags));

    cache->cache.ops->put_object(&xobject->fscache);
    goto try_again;

requeue:
    clear_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags);
    cache->cache.ops->put_object(&xobject->fscache);
    _leave(" = -ETIMEDOUT");
    return -ETIMEDOUT;
}

/*
 * delete an object representation from the cache
 * - file backed objects are unlinked
 * - directory backed objects are stuffed into the graveyard for userspace to
 *   delete
 * - unlocks the directory mutex
 */
static int cachefiles_bury_object(struct cachefiles_cache *cache,
                  struct dentry *dir,
                  struct dentry *rep,
                  bool preemptive)
{
    struct dentry *grave, *trap;
    struct path path, path_to_graveyard;
    char nbuffer[8 + 8 + 1];
    int ret;

    _enter(",'%*.*s','%*.*s'",
           dir->d_name.len, dir->d_name.len, dir->d_name.name,
           rep->d_name.len, rep->d_name.len, rep->d_name.name);

    _debug("remove %p from %p", rep, dir);

    /* non-directories can just be unlinked */
    if (!S_ISDIR(rep->d_inode->i_mode)) {
        _debug("unlink stale object");

        path.mnt = cache->mnt;
        path.dentry = dir;
        ret = security_path_unlink(&path, rep);
        if (ret < 0) {
            cachefiles_io_error(cache, "Unlink security error");
        } else {
            ret = vfs_unlink(dir->d_inode, rep);

            if (preemptive)
                cachefiles_mark_object_buried(cache, rep);
        }

        mutex_unlock(&dir->d_inode->i_mutex);

        if (ret == -EIO)
            cachefiles_io_error(cache, "Unlink failed");

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

    /* directories have to be moved to the graveyard */
    _debug("move stale object to graveyard");
    mutex_unlock(&dir->d_inode->i_mutex);

try_again:
    /* first step is to make up a grave dentry in the graveyard */
    sprintf(nbuffer, "%08x%08x",
        (uint32_t) get_seconds(),
        (uint32_t) atomic_inc_return(&cache->gravecounter));

    /* do the multiway lock magic */
    trap = lock_rename(cache->graveyard, dir);

    /* do some checks before getting the grave dentry */
    if (rep->d_parent != dir) {
        /* the entry was probably culled when we dropped the parent dir
         * lock */
        unlock_rename(cache->graveyard, dir);
        _leave(" = 0 [culled?]");
        return 0;
    }

    if (!S_ISDIR(cache->graveyard->d_inode->i_mode)) {
        unlock_rename(cache->graveyard, dir);
        cachefiles_io_error(cache, "Graveyard no longer a directory");
        return -EIO;
    }

    if (trap == rep) {
        unlock_rename(cache->graveyard, dir);
        cachefiles_io_error(cache, "May not make directory loop");
        return -EIO;
    }

    if (d_mountpoint(rep)) {
        unlock_rename(cache->graveyard, dir);
        cachefiles_io_error(cache, "Mountpoint in cache");
        return -EIO;
    }

    grave = lookup_one_len(nbuffer, cache->graveyard, strlen(nbuffer));
    if (IS_ERR(grave)) {
        unlock_rename(cache->graveyard, dir);

        if (PTR_ERR(grave) == -ENOMEM) {
            _leave(" = -ENOMEM");
            return -ENOMEM;
        }

        cachefiles_io_error(cache, "Lookup error %ld",
                    PTR_ERR(grave));
        return -EIO;
    }

    if (grave->d_inode) {
        unlock_rename(cache->graveyard, dir);
        dput(grave);
        grave = NULL;
        cond_resched();
        goto try_again;
    }

    if (d_mountpoint(grave)) {
        unlock_rename(cache->graveyard, dir);
        dput(grave);
        cachefiles_io_error(cache, "Mountpoint in graveyard");
        return -EIO;
    }

    /* target should not be an ancestor of source */
    if (trap == grave) {
        unlock_rename(cache->graveyard, dir);
        dput(grave);
        cachefiles_io_error(cache, "May not make directory loop");
        return -EIO;
    }

    /* attempt the rename */
    path.mnt = cache->mnt;
    path.dentry = dir;
    path_to_graveyard.mnt = cache->mnt;
    path_to_graveyard.dentry = cache->graveyard;
    ret = security_path_rename(&path, rep, &path_to_graveyard, grave);
    if (ret < 0) {
        cachefiles_io_error(cache, "Rename security error %d", ret);
    } else {
        ret = vfs_rename(dir->d_inode, rep,
                 cache->graveyard->d_inode, grave);
        if (ret != 0 && ret != -ENOMEM)
            cachefiles_io_error(cache,
                        "Rename failed with error %d", ret);

        if (preemptive)
            cachefiles_mark_object_buried(cache, rep);
    }

    unlock_rename(cache->graveyard, dir);
    dput(grave);
    _leave(" = 0");
    return 0;
}

/*
 * delete an object representation from the cache
 */
int cachefiles_delete_object(struct cachefiles_cache *cache,
                 struct cachefiles_object *object)
{
    struct dentry *dir;
    int ret;

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

    ASSERT(object->dentry);
    ASSERT(object->dentry->d_inode);
    ASSERT(object->dentry->d_parent);

    dir = dget_parent(object->dentry);

    mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_PARENT);

    if (test_bit(CACHEFILES_OBJECT_BURIED, &object->flags)) {
        /* object allocation for the same key preemptively deleted this
         * object's file so that it could create its own file */
        _debug("object preemptively buried");
        mutex_unlock(&dir->d_inode->i_mutex);
        ret = 0;
    } else {
        /* we need to check that our parent is _still_ our parent - it
         * may have been renamed */
        if (dir == object->dentry->d_parent) {
            ret = cachefiles_bury_object(cache, dir,
                             object->dentry, false);
        } else {
            /* it got moved, presumably by cachefilesd culling it,
             * so it's no longer in the key path and we can ignore
             * it */
            mutex_unlock(&dir->d_inode->i_mutex);
            ret = 0;
        }
    }

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

/*
 * walk from the parent object to the child object through the backing
 * filesystem, creating directories as we go
 */
int cachefiles_walk_to_object(struct cachefiles_object *parent,
                  struct cachefiles_object *object,
                  const char *key,
                  struct cachefiles_xattr *auxdata)
{
    struct cachefiles_cache *cache;
    struct dentry *dir, *next = NULL;
    struct path path;
    unsigned long start;
    const char *name;
    int ret, nlen;

    _enter("OBJ%x{%p},OBJ%x,%s,",
           parent->fscache.debug_id, parent->dentry,
           object->fscache.debug_id, key);

    cache = container_of(parent->fscache.cache,
                 struct cachefiles_cache, cache);
    path.mnt = cache->mnt;

    ASSERT(parent->dentry);
    ASSERT(parent->dentry->d_inode);

    if (!(S_ISDIR(parent->dentry->d_inode->i_mode))) {
        // TODO: convert file to dir
        _leave("looking up in none directory");
        return -ENOBUFS;
    }

    dir = dget(parent->dentry);

advance:
    /* attempt to transit the first directory component */
    name = key;
    nlen = strlen(key);

    /* key ends in a double NUL */
    key = key + nlen + 1;
    if (!*key)
        key = NULL;

lookup_again:
    /* search the current directory for the element name */
    _debug("lookup '%s'", name);

    mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_PARENT);

    start = jiffies;
    next = lookup_one_len(name, dir, nlen);
    cachefiles_hist(cachefiles_lookup_histogram, start);
    if (IS_ERR(next))
        goto lookup_error;

    _debug("next -> %p %s", next, next->d_inode ? "positive" : "negative");

    if (!key)
        object->new = !next->d_inode;

    /* if this element of the path doesn't exist, then the lookup phase
     * failed, and we can release any readers in the certain knowledge that
     * there's nothing for them to actually read */
    if (!next->d_inode)
        fscache_object_lookup_negative(&object->fscache);

    /* we need to create the object if it's negative */
    if (key || object->type == FSCACHE_COOKIE_TYPE_INDEX) {
        /* index objects and intervening tree levels must be subdirs */
        if (!next->d_inode) {
            ret = cachefiles_has_space(cache, 1, 0);
            if (ret < 0)
                goto create_error;

            path.dentry = dir;
            ret = security_path_mkdir(&path, next, 0);
            if (ret < 0)
                goto create_error;
            start = jiffies;
            ret = vfs_mkdir(dir->d_inode, next, 0);
            cachefiles_hist(cachefiles_mkdir_histogram, start);
            if (ret < 0)
                goto create_error;

            ASSERT(next->d_inode);

            _debug("mkdir -> %p{%p{ino=%lu}}",
                   next, next->d_inode, next->d_inode->i_ino);

        } else if (!S_ISDIR(next->d_inode->i_mode)) {
            kerror("inode %lu is not a directory",
                   next->d_inode->i_ino);
            ret = -ENOBUFS;
            goto error;
        }

    } else {
        /* non-index objects start out life as files */
        if (!next->d_inode) {
            ret = cachefiles_has_space(cache, 1, 0);
            if (ret < 0)
                goto create_error;

            path.dentry = dir;
            ret = security_path_mknod(&path, next, S_IFREG, 0);
            if (ret < 0)
                goto create_error;
            start = jiffies;
            ret = vfs_create(dir->d_inode, next, S_IFREG, true);
            cachefiles_hist(cachefiles_create_histogram, start);
            if (ret < 0)
                goto create_error;

            ASSERT(next->d_inode);

            _debug("create -> %p{%p{ino=%lu}}",
                   next, next->d_inode, next->d_inode->i_ino);

        } else if (!S_ISDIR(next->d_inode->i_mode) &&
               !S_ISREG(next->d_inode->i_mode)
               ) {
            kerror("inode %lu is not a file or directory",
                   next->d_inode->i_ino);
            ret = -ENOBUFS;
            goto error;
        }
    }

    /* process the next component */
    if (key) {
        _debug("advance");
        mutex_unlock(&dir->d_inode->i_mutex);
        dput(dir);
        dir = next;
        next = NULL;
        goto advance;
    }

    /* we've found the object we were looking for */
    object->dentry = next;

    /* if we've found that the terminal object exists, then we need to
     * check its attributes and delete it if it's out of date */
    if (!object->new) {
        _debug("validate '%*.*s'",
               next->d_name.len, next->d_name.len, next->d_name.name);

        ret = cachefiles_check_object_xattr(object, auxdata);
        if (ret == -ESTALE) {
            /* delete the object (the deleter drops the directory
             * mutex) */
            object->dentry = NULL;

            ret = cachefiles_bury_object(cache, dir, next, true);
            dput(next);
            next = NULL;

            if (ret < 0)
                goto delete_error;

            _debug("redo lookup");
            goto lookup_again;
        }
    }

    /* note that we're now using this object */
    ret = cachefiles_mark_object_active(cache, object);

    mutex_unlock(&dir->d_inode->i_mutex);
    dput(dir);
    dir = NULL;

    if (ret == -ETIMEDOUT)
        goto mark_active_timed_out;

    _debug("=== OBTAINED_OBJECT ===");

    if (object->new) {
        /* attach data to a newly constructed terminal object */
        ret = cachefiles_set_object_xattr(object, auxdata);
        if (ret < 0)
            goto check_error;
    } else {
        /* always update the atime on an object we've just looked up
         * (this is used to keep track of culling, and atimes are only
         * updated by read, write and readdir but not lookup or
         * open) */
        path.dentry = next;
        touch_atime(&path);
    }

    /* open a file interface onto a data file */
    if (object->type != FSCACHE_COOKIE_TYPE_INDEX) {
        if (S_ISREG(object->dentry->d_inode->i_mode)) {
            const struct address_space_operations *aops;

            ret = -EPERM;
            aops = object->dentry->d_inode->i_mapping->a_ops;
            if (!aops->bmap)
                goto check_error;

            object->backer = object->dentry;
        } else {
            BUG(); // TODO: open file in data-class subdir
        }
    }

    object->new = 0;
    fscache_obtained_object(&object->fscache);

    _leave(" = 0 [%lu]", object->dentry->d_inode->i_ino);
    return 0;

create_error:
    _debug("create error %d", ret);
    if (ret == -EIO)
        cachefiles_io_error(cache, "Create/mkdir failed");
    goto error;

mark_active_timed_out:
    _debug("mark active timed out");
    goto release_dentry;

check_error:
    _debug("check error %d", ret);
    write_lock(&cache->active_lock);
    rb_erase(&object->active_node, &cache->active_nodes);
    clear_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags);
    wake_up_bit(&object->flags, CACHEFILES_OBJECT_ACTIVE);
    write_unlock(&cache->active_lock);
release_dentry:
    dput(object->dentry);
    object->dentry = NULL;
    goto error_out;

delete_error:
    _debug("delete error %d", ret);
    goto error_out2;

lookup_error:
    _debug("lookup error %ld", PTR_ERR(next));
    ret = PTR_ERR(next);
    if (ret == -EIO)
        cachefiles_io_error(cache, "Lookup failed");
    next = NULL;
error:
    mutex_unlock(&dir->d_inode->i_mutex);
    dput(next);
error_out2:
    dput(dir);
error_out:
    _leave(" = error %d", -ret);
    return ret;
}

/*
 * get a subdirectory
 */
struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
                    struct dentry *dir,
                    const char *dirname)
{
    struct dentry *subdir;
    unsigned long start;
    struct path path;
    int ret;

    _enter(",,%s", dirname);

    /* search the current directory for the element name */
    mutex_lock(&dir->d_inode->i_mutex);

    start = jiffies;
    subdir = lookup_one_len(dirname, dir, strlen(dirname));
    cachefiles_hist(cachefiles_lookup_histogram, start);
    if (IS_ERR(subdir)) {
        if (PTR_ERR(subdir) == -ENOMEM)
            goto nomem_d_alloc;
        goto lookup_error;
    }

    _debug("subdir -> %p %s",
           subdir, subdir->d_inode ? "positive" : "negative");

    /* we need to create the subdir if it doesn't exist yet */
    if (!subdir->d_inode) {
        ret = cachefiles_has_space(cache, 1, 0);
        if (ret < 0)
            goto mkdir_error;

        _debug("attempt mkdir");

        path.mnt = cache->mnt;
        path.dentry = dir;
        ret = security_path_mkdir(&path, subdir, 0700);
        if (ret < 0)
            goto mkdir_error;
        ret = vfs_mkdir(dir->d_inode, subdir, 0700);
        if (ret < 0)
            goto mkdir_error;

        ASSERT(subdir->d_inode);

        _debug("mkdir -> %p{%p{ino=%lu}}",
               subdir,
               subdir->d_inode,
               subdir->d_inode->i_ino);
    }

    mutex_unlock(&dir->d_inode->i_mutex);

    /* we need to make sure the subdir is a directory */
    ASSERT(subdir->d_inode);

    if (!S_ISDIR(subdir->d_inode->i_mode)) {
        kerror("%s is not a directory", dirname);
        ret = -EIO;
        goto check_error;
    }

    ret = -EPERM;
    if (!subdir->d_inode->i_op ||
        !subdir->d_inode->i_op->setxattr ||
        !subdir->d_inode->i_op->getxattr ||
        !subdir->d_inode->i_op->lookup ||
        !subdir->d_inode->i_op->mkdir ||
        !subdir->d_inode->i_op->create ||
        !subdir->d_inode->i_op->rename ||
        !subdir->d_inode->i_op->rmdir ||
        !subdir->d_inode->i_op->unlink)
        goto check_error;

    _leave(" = [%lu]", subdir->d_inode->i_ino);
    return subdir;

check_error:
    dput(subdir);
    _leave(" = %d [check]", ret);
    return ERR_PTR(ret);

mkdir_error:
    mutex_unlock(&dir->d_inode->i_mutex);
    dput(subdir);
    kerror("mkdir %s failed with error %d", dirname, ret);
    return ERR_PTR(ret);

lookup_error:
    mutex_unlock(&dir->d_inode->i_mutex);
    ret = PTR_ERR(subdir);
    kerror("Lookup %s failed with error %d", dirname, ret);
    return ERR_PTR(ret);

nomem_d_alloc:
    mutex_unlock(&dir->d_inode->i_mutex);
    _leave(" = -ENOMEM");
    return ERR_PTR(-ENOMEM);
}

/*
 * find out if an object is in use or not
 * - if finds object and it's not in use:
 *   - returns a pointer to the object and a reference on it
 *   - returns with the directory locked
 */
static struct dentry *cachefiles_check_active(struct cachefiles_cache *cache,
                          struct dentry *dir,
                          char *filename)
{
    struct cachefiles_object *object;
    struct rb_node *_n;
    struct dentry *victim;
    unsigned long start;
    int ret;

    //_enter(",%*.*s/,%s",
    //       dir->d_name.len, dir->d_name.len, dir->d_name.name, filename);

    /* look up the victim */
    mutex_lock_nested(&dir->d_inode->i_mutex, 1);

    start = jiffies;
    victim = lookup_one_len(filename, dir, strlen(filename));
    cachefiles_hist(cachefiles_lookup_histogram, start);
    if (IS_ERR(victim))
        goto lookup_error;

    //_debug("victim -> %p %s",
    //       victim, victim->d_inode ? "positive" : "negative");

    /* if the object is no longer there then we probably retired the object
     * at the netfs's request whilst the cull was in progress
     */
    if (!victim->d_inode) {
        mutex_unlock(&dir->d_inode->i_mutex);
        dput(victim);
        _leave(" = -ENOENT [absent]");
        return ERR_PTR(-ENOENT);
    }

    /* check to see if we're using this object */
    read_lock(&cache->active_lock);

    _n = cache->active_nodes.rb_node;

    while (_n) {
        object = rb_entry(_n, struct cachefiles_object, active_node);

        if (object->dentry > victim)
            _n = _n->rb_left;
        else if (object->dentry < victim)
            _n = _n->rb_right;
        else
            goto object_in_use;
    }

    read_unlock(&cache->active_lock);

    //_leave(" = %p", victim);
    return victim;

object_in_use:
    read_unlock(&cache->active_lock);
    mutex_unlock(&dir->d_inode->i_mutex);
    dput(victim);
    //_leave(" = -EBUSY [in use]");
    return ERR_PTR(-EBUSY);

lookup_error:
    mutex_unlock(&dir->d_inode->i_mutex);
    ret = PTR_ERR(victim);
    if (ret == -ENOENT) {
        /* file or dir now absent - probably retired by netfs */
        _leave(" = -ESTALE [absent]");
        return ERR_PTR(-ESTALE);
    }

    if (ret == -EIO) {
        cachefiles_io_error(cache, "Lookup failed");
    } else if (ret != -ENOMEM) {
        kerror("Internal error: %d", ret);
        ret = -EIO;
    }

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

/*
 * cull an object if it's not in use
 * - called only by cache manager daemon
 */
int cachefiles_cull(struct cachefiles_cache *cache, struct dentry *dir,
            char *filename)
{
    struct dentry *victim;
    int ret;

    _enter(",%*.*s/,%s",
           dir->d_name.len, dir->d_name.len, dir->d_name.name, filename);

    victim = cachefiles_check_active(cache, dir, filename);
    if (IS_ERR(victim))
        return PTR_ERR(victim);

    _debug("victim -> %p %s",
           victim, victim->d_inode ? "positive" : "negative");

    /* okay... the victim is not being used so we can cull it
     * - start by marking it as stale
     */
    _debug("victim is cullable");

    ret = cachefiles_remove_object_xattr(cache, victim);
    if (ret < 0)
        goto error_unlock;

    /*  actually remove the victim (drops the dir mutex) */
    _debug("bury");

    ret = cachefiles_bury_object(cache, dir, victim, false);
    if (ret < 0)
        goto error;

    dput(victim);
    _leave(" = 0");
    return 0;

error_unlock:
    mutex_unlock(&dir->d_inode->i_mutex);
error:
    dput(victim);
    if (ret == -ENOENT) {
        /* file or dir now absent - probably retired by netfs */
        _leave(" = -ESTALE [absent]");
        return -ESTALE;
    }

    if (ret != -ENOMEM) {
        kerror("Internal error: %d", ret);
        ret = -EIO;
    }

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

/*
 * find out if an object is in use or not
 * - called only by cache manager daemon
 * - returns -EBUSY or 0 to indicate whether an object is in use or not
 */
int cachefiles_check_in_use(struct cachefiles_cache *cache, struct dentry *dir,
                char *filename)
{
    struct dentry *victim;

    //_enter(",%*.*s/,%s",
    //       dir->d_name.len, dir->d_name.len, dir->d_name.name, filename);

    victim = cachefiles_check_active(cache, dir, filename);
    if (IS_ERR(victim))
        return PTR_ERR(victim);

    mutex_unlock(&dir->d_inode->i_mutex);
    dput(victim);
    //_leave(" = 0");
    return 0;
}