blob: 7bf7a5fcc045f86a98881657e6da2acc06be98dc [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0-or-later
/* CacheFiles path walking and related routines
*
* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#include <linux/fs.h>
#include <linux/namei.h>
#include "internal.h"
/*
* Mark the backing file as being a cache file if it's not already in use. The
* mark tells the culling request command that it's not allowed to cull the
* file or directory. The caller must hold the inode lock.
*/
static bool __cachefiles_mark_inode_in_use(struct cachefiles_object *object,
struct inode *inode)
{
bool can_use = false;
if (!(inode->i_flags & S_KERNEL_FILE)) {
inode->i_flags |= S_KERNEL_FILE;
trace_cachefiles_mark_active(object, inode);
can_use = true;
} else {
trace_cachefiles_mark_failed(object, inode);
}
return can_use;
}
static bool cachefiles_mark_inode_in_use(struct cachefiles_object *object,
struct inode *inode)
{
bool can_use;
inode_lock(inode);
can_use = __cachefiles_mark_inode_in_use(object, inode);
inode_unlock(inode);
return can_use;
}
/*
* Unmark a backing inode. The caller must hold the inode lock.
*/
static void __cachefiles_unmark_inode_in_use(struct cachefiles_object *object,
struct inode *inode)
{
inode->i_flags &= ~S_KERNEL_FILE;
trace_cachefiles_mark_inactive(object, inode);
}
static void cachefiles_do_unmark_inode_in_use(struct cachefiles_object *object,
struct inode *inode)
{
inode_lock(inode);
__cachefiles_unmark_inode_in_use(object, inode);
inode_unlock(inode);
}
/*
* Unmark a backing inode and tell cachefilesd that there's something that can
* be culled.
*/
void cachefiles_unmark_inode_in_use(struct cachefiles_object *object,
struct file *file)
{
struct cachefiles_cache *cache = object->volume->cache;
struct inode *inode = file_inode(file);
cachefiles_do_unmark_inode_in_use(object, inode);
if (!test_bit(CACHEFILES_OBJECT_USING_TMPFILE, &object->flags)) {
atomic_long_add(inode->i_blocks, &cache->b_released);
if (atomic_inc_return(&cache->f_released))
cachefiles_state_changed(cache);
}
}
/*
* get a subdirectory
*/
struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
struct dentry *dir,
const char *dirname,
bool *_is_new)
{
struct dentry *subdir;
struct path path;
int ret;
_enter(",,%s", dirname);
/* search the current directory for the element name */
inode_lock_nested(d_inode(dir), I_MUTEX_PARENT);
retry:
ret = cachefiles_inject_read_error();
if (ret == 0)
subdir = lookup_one_len(dirname, dir, strlen(dirname));
else
subdir = ERR_PTR(ret);
trace_cachefiles_lookup(NULL, dir, subdir);
if (IS_ERR(subdir)) {
trace_cachefiles_vfs_error(NULL, d_backing_inode(dir),
PTR_ERR(subdir),
cachefiles_trace_lookup_error);
if (PTR_ERR(subdir) == -ENOMEM)
goto nomem_d_alloc;
goto lookup_error;
}
_debug("subdir -> %pd %s",
subdir, d_backing_inode(subdir) ? "positive" : "negative");
/* we need to create the subdir if it doesn't exist yet */
if (d_is_negative(subdir)) {
ret = cachefiles_has_space(cache, 1, 0,
cachefiles_has_space_for_create);
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 = cachefiles_inject_write_error();
if (ret == 0)
ret = vfs_mkdir(&nop_mnt_idmap, d_inode(dir), subdir, 0700);
if (ret < 0) {
trace_cachefiles_vfs_error(NULL, d_inode(dir), ret,
cachefiles_trace_mkdir_error);
goto mkdir_error;
}
trace_cachefiles_mkdir(dir, subdir);
if (unlikely(d_unhashed(subdir))) {
cachefiles_put_directory(subdir);
goto retry;
}
ASSERT(d_backing_inode(subdir));
_debug("mkdir -> %pd{ino=%lu}",
subdir, d_backing_inode(subdir)->i_ino);
if (_is_new)
*_is_new = true;
}
/* Tell rmdir() it's not allowed to delete the subdir */
inode_lock(d_inode(subdir));
inode_unlock(d_inode(dir));
if (!__cachefiles_mark_inode_in_use(NULL, d_inode(subdir))) {
pr_notice("cachefiles: Inode already in use: %pd (B=%lx)\n",
subdir, d_inode(subdir)->i_ino);
goto mark_error;
}
inode_unlock(d_inode(subdir));
/* we need to make sure the subdir is a directory */
ASSERT(d_backing_inode(subdir));
if (!d_can_lookup(subdir)) {
pr_err("%s is not a directory\n", dirname);
ret = -EIO;
goto check_error;
}
ret = -EPERM;
if (!(d_backing_inode(subdir)->i_opflags & IOP_XATTR) ||
!d_backing_inode(subdir)->i_op->lookup ||
!d_backing_inode(subdir)->i_op->mkdir ||
!d_backing_inode(subdir)->i_op->rename ||
!d_backing_inode(subdir)->i_op->rmdir ||
!d_backing_inode(subdir)->i_op->unlink)
goto check_error;
_leave(" = [%lu]", d_backing_inode(subdir)->i_ino);
return subdir;
check_error:
cachefiles_put_directory(subdir);
_leave(" = %d [check]", ret);
return ERR_PTR(ret);
mark_error:
inode_unlock(d_inode(subdir));
dput(subdir);
return ERR_PTR(-EBUSY);
mkdir_error:
inode_unlock(d_inode(dir));
dput(subdir);
pr_err("mkdir %s failed with error %d\n", dirname, ret);
return ERR_PTR(ret);
lookup_error:
inode_unlock(d_inode(dir));
ret = PTR_ERR(subdir);
pr_err("Lookup %s failed with error %d\n", dirname, ret);
return ERR_PTR(ret);
nomem_d_alloc:
inode_unlock(d_inode(dir));
_leave(" = -ENOMEM");
return ERR_PTR(-ENOMEM);
}
/*
* Put a subdirectory.
*/
void cachefiles_put_directory(struct dentry *dir)
{
if (dir) {
cachefiles_do_unmark_inode_in_use(NULL, d_inode(dir));
dput(dir);
}
}
/*
* Remove a regular file from the cache.
*/
static int cachefiles_unlink(struct cachefiles_cache *cache,
struct cachefiles_object *object,
struct dentry *dir, struct dentry *dentry,
enum fscache_why_object_killed why)
{
struct path path = {
.mnt = cache->mnt,
.dentry = dir,
};
int ret;
trace_cachefiles_unlink(object, d_inode(dentry)->i_ino, why);
ret = security_path_unlink(&path, dentry);
if (ret < 0) {
cachefiles_io_error(cache, "Unlink security error");
return ret;
}
ret = cachefiles_inject_remove_error();
if (ret == 0) {
ret = vfs_unlink(&nop_mnt_idmap, d_backing_inode(dir), dentry, NULL);
if (ret == -EIO)
cachefiles_io_error(cache, "Unlink failed");
}
if (ret != 0)
trace_cachefiles_vfs_error(object, d_backing_inode(dir), ret,
cachefiles_trace_unlink_error);
return ret;
}
/*
* Delete an object representation from the cache
* - File backed objects are unlinked
* - Directory backed objects are stuffed into the graveyard for userspace to
* delete
*/
int cachefiles_bury_object(struct cachefiles_cache *cache,
struct cachefiles_object *object,
struct dentry *dir,
struct dentry *rep,
enum fscache_why_object_killed why)
{
struct dentry *grave, *trap;
struct path path, path_to_graveyard;
char nbuffer[8 + 8 + 1];
int ret;
_enter(",'%pd','%pd'", dir, rep);
if (rep->d_parent != dir) {
inode_unlock(d_inode(dir));
_leave(" = -ESTALE");
return -ESTALE;
}
/* non-directories can just be unlinked */
if (!d_is_dir(rep)) {
dget(rep); /* Stop the dentry being negated if it's only pinned
* by a file struct.
*/
ret = cachefiles_unlink(cache, object, dir, rep, why);
dput(rep);
inode_unlock(d_inode(dir));
_leave(" = %d", ret);
return ret;
}
/* directories have to be moved to the graveyard */
_debug("move stale object to graveyard");
inode_unlock(d_inode(dir));
try_again:
/* first step is to make up a grave dentry in the graveyard */
sprintf(nbuffer, "%08x%08x",
(uint32_t) ktime_get_real_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 || IS_DEADDIR(d_inode(rep))) {
/* the entry was probably culled when we dropped the parent dir
* lock */
unlock_rename(cache->graveyard, dir);
_leave(" = 0 [culled?]");
return 0;
}
if (!d_can_lookup(cache->graveyard)) {
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);
trace_cachefiles_vfs_error(object, d_inode(cache->graveyard),
PTR_ERR(grave),
cachefiles_trace_lookup_error);
if (PTR_ERR(grave) == -ENOMEM) {
_leave(" = -ENOMEM");
return -ENOMEM;
}
cachefiles_io_error(cache, "Lookup error %ld", PTR_ERR(grave));
return -EIO;
}
if (d_is_positive(grave)) {
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, 0);
if (ret < 0) {
cachefiles_io_error(cache, "Rename security error %d", ret);
} else {
struct renamedata rd = {
.old_mnt_idmap = &nop_mnt_idmap,
.old_dir = d_inode(dir),
.old_dentry = rep,
.new_mnt_idmap = &nop_mnt_idmap,
.new_dir = d_inode(cache->graveyard),
.new_dentry = grave,
};
trace_cachefiles_rename(object, d_inode(rep)->i_ino, why);
ret = cachefiles_inject_read_error();
if (ret == 0)
ret = vfs_rename(&rd);
if (ret != 0)
trace_cachefiles_vfs_error(object, d_inode(dir), ret,
cachefiles_trace_rename_error);
if (ret != 0 && ret != -ENOMEM)
cachefiles_io_error(cache,
"Rename failed with error %d", ret);
}
__cachefiles_unmark_inode_in_use(object, d_inode(rep));
unlock_rename(cache->graveyard, dir);
dput(grave);
_leave(" = 0");
return 0;
}
/*
* Delete a cache file.
*/
int cachefiles_delete_object(struct cachefiles_object *object,
enum fscache_why_object_killed why)
{
struct cachefiles_volume *volume = object->volume;
struct dentry *dentry = object->file->f_path.dentry;
struct dentry *fan = volume->fanout[(u8)object->cookie->key_hash];
int ret;
_enter(",OBJ%x{%pD}", object->debug_id, object->file);
/* Stop the dentry being negated if it's only pinned by a file struct. */
dget(dentry);
inode_lock_nested(d_backing_inode(fan), I_MUTEX_PARENT);
ret = cachefiles_unlink(volume->cache, object, fan, dentry, why);
inode_unlock(d_backing_inode(fan));
dput(dentry);
return ret;
}
/*
* Create a temporary file and leave it unattached and un-xattr'd until the
* time comes to discard the object from memory.
*/
struct file *cachefiles_create_tmpfile(struct cachefiles_object *object)
{
struct cachefiles_volume *volume = object->volume;
struct cachefiles_cache *cache = volume->cache;
const struct cred *saved_cred;
struct dentry *fan = volume->fanout[(u8)object->cookie->key_hash];
struct file *file;
const struct path parentpath = { .mnt = cache->mnt, .dentry = fan };
uint64_t ni_size;
long ret;
cachefiles_begin_secure(cache, &saved_cred);
ret = cachefiles_inject_write_error();
if (ret == 0) {
file = kernel_tmpfile_open(&nop_mnt_idmap, &parentpath,
S_IFREG | 0600,
O_RDWR | O_LARGEFILE | O_DIRECT,
cache->cache_cred);
ret = PTR_ERR_OR_ZERO(file);
}
if (ret) {
trace_cachefiles_vfs_error(object, d_inode(fan), ret,
cachefiles_trace_tmpfile_error);
if (ret == -EIO)
cachefiles_io_error_obj(object, "Failed to create tmpfile");
goto err;
}
trace_cachefiles_tmpfile(object, file_inode(file));
/* This is a newly created file with no other possible user */
if (!cachefiles_mark_inode_in_use(object, file_inode(file)))
WARN_ON(1);
ret = cachefiles_ondemand_init_object(object);
if (ret < 0)
goto err_unuse;
ni_size = object->cookie->object_size;
ni_size = round_up(ni_size, CACHEFILES_DIO_BLOCK_SIZE);
if (ni_size > 0) {
trace_cachefiles_trunc(object, file_inode(file), 0, ni_size,
cachefiles_trunc_expand_tmpfile);
ret = cachefiles_inject_write_error();
if (ret == 0)
ret = vfs_truncate(&file->f_path, ni_size);
if (ret < 0) {
trace_cachefiles_vfs_error(
object, file_inode(file), ret,
cachefiles_trace_trunc_error);
goto err_unuse;
}
}
ret = -EINVAL;
if (unlikely(!file->f_op->read_iter) ||
unlikely(!file->f_op->write_iter)) {
fput(file);
pr_notice("Cache does not support read_iter and write_iter\n");
goto err_unuse;
}
out:
cachefiles_end_secure(cache, saved_cred);
return file;
err_unuse:
cachefiles_do_unmark_inode_in_use(object, file_inode(file));
fput(file);
err:
file = ERR_PTR(ret);
goto out;
}
/*
* Create a new file.
*/
static bool cachefiles_create_file(struct cachefiles_object *object)
{
struct file *file;
int ret;
ret = cachefiles_has_space(object->volume->cache, 1, 0,
cachefiles_has_space_for_create);
if (ret < 0)
return false;
file = cachefiles_create_tmpfile(object);
if (IS_ERR(file))
return false;
set_bit(FSCACHE_COOKIE_NEEDS_UPDATE, &object->cookie->flags);
set_bit(CACHEFILES_OBJECT_USING_TMPFILE, &object->flags);
_debug("create -> %pD{ino=%lu}", file, file_inode(file)->i_ino);
object->file = file;
return true;
}
/*
* Open an existing file, checking its attributes and replacing it if it is
* stale.
*/
static bool cachefiles_open_file(struct cachefiles_object *object,
struct dentry *dentry)
{
struct cachefiles_cache *cache = object->volume->cache;
struct file *file;
struct path path;
int ret;
_enter("%pd", dentry);
if (!cachefiles_mark_inode_in_use(object, d_inode(dentry))) {
pr_notice("cachefiles: Inode already in use: %pd (B=%lx)\n",
dentry, d_inode(dentry)->i_ino);
return false;
}
/* We need to open a file interface onto a data file now as we can't do
* it on demand because writeback called from do_exit() sees
* current->fs == NULL - which breaks d_path() called from ext4 open.
*/
path.mnt = cache->mnt;
path.dentry = dentry;
file = kernel_file_open(&path, O_RDWR | O_LARGEFILE | O_DIRECT,
d_backing_inode(dentry), cache->cache_cred);
if (IS_ERR(file)) {
trace_cachefiles_vfs_error(object, d_backing_inode(dentry),
PTR_ERR(file),
cachefiles_trace_open_error);
goto error;
}
if (unlikely(!file->f_op->read_iter) ||
unlikely(!file->f_op->write_iter)) {
pr_notice("Cache does not support read_iter and write_iter\n");
goto error_fput;
}
_debug("file -> %pd positive", dentry);
ret = cachefiles_ondemand_init_object(object);
if (ret < 0)
goto error_fput;
ret = cachefiles_check_auxdata(object, file);
if (ret < 0)
goto check_failed;
clear_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &object->cookie->flags);
object->file = file;
/* 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).
*/
touch_atime(&file->f_path);
dput(dentry);
return true;
check_failed:
fscache_cookie_lookup_negative(object->cookie);
cachefiles_unmark_inode_in_use(object, file);
fput(file);
dput(dentry);
if (ret == -ESTALE)
return cachefiles_create_file(object);
return false;
error_fput:
fput(file);
error:
cachefiles_do_unmark_inode_in_use(object, d_inode(dentry));
dput(dentry);
return false;
}
/*
* walk from the parent object to the child object through the backing
* filesystem, creating directories as we go
*/
bool cachefiles_look_up_object(struct cachefiles_object *object)
{
struct cachefiles_volume *volume = object->volume;
struct dentry *dentry, *fan = volume->fanout[(u8)object->cookie->key_hash];
int ret;
_enter("OBJ%x,%s,", object->debug_id, object->d_name);
/* Look up path "cache/vol/fanout/file". */
ret = cachefiles_inject_read_error();
if (ret == 0)
dentry = lookup_positive_unlocked(object->d_name, fan,
object->d_name_len);
else
dentry = ERR_PTR(ret);
trace_cachefiles_lookup(object, fan, dentry);
if (IS_ERR(dentry)) {
if (dentry == ERR_PTR(-ENOENT))
goto new_file;
if (dentry == ERR_PTR(-EIO))
cachefiles_io_error_obj(object, "Lookup failed");
return false;
}
if (!d_is_reg(dentry)) {
pr_err("%pd is not a file\n", dentry);
inode_lock_nested(d_inode(fan), I_MUTEX_PARENT);
ret = cachefiles_bury_object(volume->cache, object, fan, dentry,
FSCACHE_OBJECT_IS_WEIRD);
dput(dentry);
if (ret < 0)
return false;
goto new_file;
}
if (!cachefiles_open_file(object, dentry))
return false;
_leave(" = t [%lu]", file_inode(object->file)->i_ino);
return true;
new_file:
fscache_cookie_lookup_negative(object->cookie);
return cachefiles_create_file(object);
}
/*
* Attempt to link a temporary file into its rightful place in the cache.
*/
bool cachefiles_commit_tmpfile(struct cachefiles_cache *cache,
struct cachefiles_object *object)
{
struct cachefiles_volume *volume = object->volume;
struct dentry *dentry, *fan = volume->fanout[(u8)object->cookie->key_hash];
bool success = false;
int ret;
_enter(",%pD", object->file);
inode_lock_nested(d_inode(fan), I_MUTEX_PARENT);
ret = cachefiles_inject_read_error();
if (ret == 0)
dentry = lookup_one_len(object->d_name, fan, object->d_name_len);
else
dentry = ERR_PTR(ret);
if (IS_ERR(dentry)) {
trace_cachefiles_vfs_error(object, d_inode(fan), PTR_ERR(dentry),
cachefiles_trace_lookup_error);
_debug("lookup fail %ld", PTR_ERR(dentry));
goto out_unlock;
}
if (!d_is_negative(dentry)) {
if (d_backing_inode(dentry) == file_inode(object->file)) {
success = true;
goto out_dput;
}
ret = cachefiles_unlink(volume->cache, object, fan, dentry,
FSCACHE_OBJECT_IS_STALE);
if (ret < 0)
goto out_dput;
dput(dentry);
ret = cachefiles_inject_read_error();
if (ret == 0)
dentry = lookup_one_len(object->d_name, fan, object->d_name_len);
else
dentry = ERR_PTR(ret);
if (IS_ERR(dentry)) {
trace_cachefiles_vfs_error(object, d_inode(fan), PTR_ERR(dentry),
cachefiles_trace_lookup_error);
_debug("lookup fail %ld", PTR_ERR(dentry));
goto out_unlock;
}
}
ret = cachefiles_inject_read_error();
if (ret == 0)
ret = vfs_link(object->file->f_path.dentry, &nop_mnt_idmap,
d_inode(fan), dentry, NULL);
if (ret < 0) {
trace_cachefiles_vfs_error(object, d_inode(fan), ret,
cachefiles_trace_link_error);
_debug("link fail %d", ret);
} else {
trace_cachefiles_link(object, file_inode(object->file));
spin_lock(&object->lock);
/* TODO: Do we want to switch the file pointer to the new dentry? */
clear_bit(CACHEFILES_OBJECT_USING_TMPFILE, &object->flags);
spin_unlock(&object->lock);
success = true;
}
out_dput:
dput(dentry);
out_unlock:
inode_unlock(d_inode(fan));
_leave(" = %u", success);
return success;
}
/*
* Look up an inode to be checked or culled. Return -EBUSY if the inode is
* marked in use.
*/
static struct dentry *cachefiles_lookup_for_cull(struct cachefiles_cache *cache,
struct dentry *dir,
char *filename)
{
struct dentry *victim;
int ret = -ENOENT;
inode_lock_nested(d_inode(dir), I_MUTEX_PARENT);
victim = lookup_one_len(filename, dir, strlen(filename));
if (IS_ERR(victim))
goto lookup_error;
if (d_is_negative(victim))
goto lookup_put;
if (d_inode(victim)->i_flags & S_KERNEL_FILE)
goto lookup_busy;
return victim;
lookup_busy:
ret = -EBUSY;
lookup_put:
inode_unlock(d_inode(dir));
dput(victim);
return ERR_PTR(ret);
lookup_error:
inode_unlock(d_inode(dir));
ret = PTR_ERR(victim);
if (ret == -ENOENT)
return ERR_PTR(-ESTALE); /* Probably got retired by the netfs */
if (ret == -EIO) {
cachefiles_io_error(cache, "Lookup failed");
} else if (ret != -ENOMEM) {
pr_err("Internal error: %d\n", ret);
ret = -EIO;
}
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;
struct inode *inode;
int ret;
_enter(",%pd/,%s", dir, filename);
victim = cachefiles_lookup_for_cull(cache, dir, filename);
if (IS_ERR(victim))
return PTR_ERR(victim);
/* check to see if someone is using this object */
inode = d_inode(victim);
inode_lock(inode);
if (inode->i_flags & S_KERNEL_FILE) {
ret = -EBUSY;
} else {
/* Stop the cache from picking it back up */
inode->i_flags |= S_KERNEL_FILE;
ret = 0;
}
inode_unlock(inode);
if (ret < 0)
goto error_unlock;
ret = cachefiles_bury_object(cache, NULL, dir, victim,
FSCACHE_OBJECT_WAS_CULLED);
if (ret < 0)
goto error;
fscache_count_culled();
dput(victim);
_leave(" = 0");
return 0;
error_unlock:
inode_unlock(d_inode(dir));
error:
dput(victim);
if (ret == -ENOENT)
return -ESTALE; /* Probably got retired by the netfs */
if (ret != -ENOMEM) {
pr_err("Internal error: %d\n", 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;
int ret = 0;
victim = cachefiles_lookup_for_cull(cache, dir, filename);
if (IS_ERR(victim))
return PTR_ERR(victim);
inode_unlock(d_inode(dir));
dput(victim);
return ret;
}