// SPDX-License-Identifier: GPL-2.0-or-later
/* Manage high-level VFS aspects of a cache.
 *
 * Copyright (C) 2007, 2021 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/slab.h>
#include <linux/statfs.h>
#include <linux/namei.h>
#include "internal.h"

/*
 * Bring a cache online.
 */
int cachefiles_add_cache(struct cachefiles_cache *cache)
{
        struct fscache_cache *cache_cookie;
        struct path path;
        struct kstatfs stats;
        struct dentry *graveyard, *cachedir, *root;
        const struct cred *saved_cred;
        int ret;

        _enter("");

        cache_cookie = fscache_acquire_cache(cache->tag);
        if (IS_ERR(cache_cookie))
                return PTR_ERR(cache_cookie);

        /* we want to work under the module's security ID */
        ret = cachefiles_get_security_ID(cache);
        if (ret < 0)
                goto error_getsec;

        cachefiles_begin_secure(cache, &saved_cred);

        /* look up the directory at the root of the cache */
        ret = kern_path(cache->rootdirname, LOOKUP_DIRECTORY, &path);
        if (ret < 0)
                goto error_open_root;

        cache->mnt = path.mnt;
        root = path.dentry;

        ret = -EINVAL;
        if (is_idmapped_mnt(path.mnt)) {
                pr_warn("File cache on idmapped mounts not supported");
                goto error_unsupported;
        }

        /* Check features of the backing filesystem:
         * - Directories must support looking up and directory creation
         * - We create tmpfiles to handle invalidation
         * - We use xattrs to store metadata
         * - We need to be able to query the amount of space available
         * - We want to be able to sync the filesystem when stopping the cache
         * - We use DIO to/from pages, so the blocksize mustn't be too big.
         */
        ret = -EOPNOTSUPP;
        if (d_is_negative(root) ||
            !d_backing_inode(root)->i_op->lookup ||
            !d_backing_inode(root)->i_op->mkdir ||
            !d_backing_inode(root)->i_op->tmpfile ||
            !(d_backing_inode(root)->i_opflags & IOP_XATTR) ||
            !root->d_sb->s_op->statfs ||
            !root->d_sb->s_op->sync_fs ||
            root->d_sb->s_blocksize > PAGE_SIZE)
                goto error_unsupported;

        ret = -EROFS;
        if (sb_rdonly(root->d_sb))
                goto error_unsupported;

        /* determine the security of the on-disk cache as this governs
         * security ID of files we create */
        ret = cachefiles_determine_cache_security(cache, root, &saved_cred);
        if (ret < 0)
                goto error_unsupported;

        /* get the cache size and blocksize */
        ret = vfs_statfs(&path, &stats);
        if (ret < 0)
                goto error_unsupported;

        ret = -ERANGE;
        if (stats.f_bsize <= 0)
                goto error_unsupported;

        ret = -EOPNOTSUPP;
        if (stats.f_bsize > PAGE_SIZE)
                goto error_unsupported;

        cache->bsize = stats.f_bsize;
        cache->bshift = ilog2(stats.f_bsize);

        _debug("blksize %u (shift %u)",
               cache->bsize, cache->bshift);

        _debug("size %llu, avail %llu",
               (unsigned long long) stats.f_blocks,
               (unsigned long long) stats.f_bavail);

        /* set up caching limits */
        do_div(stats.f_files, 100);
        cache->fstop = stats.f_files * cache->fstop_percent;
        cache->fcull = stats.f_files * cache->fcull_percent;
        cache->frun  = stats.f_files * cache->frun_percent;

        _debug("limits {%llu,%llu,%llu} files",
               (unsigned long long) cache->frun,
               (unsigned long long) cache->fcull,
               (unsigned long long) cache->fstop);

        do_div(stats.f_blocks, 100);
        cache->bstop = stats.f_blocks * cache->bstop_percent;
        cache->bcull = stats.f_blocks * cache->bcull_percent;
        cache->brun  = stats.f_blocks * cache->brun_percent;

        _debug("limits {%llu,%llu,%llu} blocks",
               (unsigned long long) cache->brun,
               (unsigned long long) cache->bcull,
               (unsigned long long) cache->bstop);

        /* get the cache directory and check its type */
        cachedir = cachefiles_get_directory(cache, root, "cache", NULL);
        if (IS_ERR(cachedir)) {
                ret = PTR_ERR(cachedir);
                goto error_unsupported;
        }

        cache->store = cachedir;

        /* get the graveyard directory */
        graveyard = cachefiles_get_directory(cache, root, "graveyard", NULL);
        if (IS_ERR(graveyard)) {
                ret = PTR_ERR(graveyard);
                goto error_unsupported;
        }

        cache->graveyard = graveyard;
        cache->cache = cache_cookie;

        ret = fscache_add_cache(cache_cookie, &cachefiles_cache_ops, cache);
        if (ret < 0)
                goto error_add_cache;

        /* done */
        set_bit(CACHEFILES_READY, &cache->flags);
        dput(root);

        pr_info("File cache on %s registered\n", cache_cookie->name);

        /* check how much space the cache has */
        cachefiles_has_space(cache, 0, 0, cachefiles_has_space_check);
        cachefiles_end_secure(cache, saved_cred);
        _leave(" = 0 [%px]", cache->cache);
        return 0;

error_add_cache:
        cachefiles_put_directory(cache->graveyard);
        cache->graveyard = NULL;
error_unsupported:
        cachefiles_put_directory(cache->store);
        cache->store = NULL;
        mntput(cache->mnt);
        cache->mnt = NULL;
        dput(root);
error_open_root:
        cachefiles_end_secure(cache, saved_cred);
error_getsec:
        fscache_relinquish_cache(cache_cookie);
        cache->cache = NULL;
        pr_err("Failed to register: %d\n", ret);
        return ret;
}

/*
 * See if we have space for a number of pages and/or a number of files in the
 * cache
 */
int cachefiles_has_space(struct cachefiles_cache *cache,
                         unsigned fnr, unsigned bnr,
                         enum cachefiles_has_space_for reason)
{
        struct kstatfs stats;
        u64 b_avail, b_writing;
        int ret;

        struct path path = {
                .mnt    = cache->mnt,
                .dentry = cache->mnt->mnt_root,
        };

        //_enter("{%llu,%llu,%llu,%llu,%llu,%llu},%u,%u",
        //       (unsigned long long) cache->frun,
        //       (unsigned long long) cache->fcull,
        //       (unsigned long long) cache->fstop,
        //       (unsigned long long) cache->brun,
        //       (unsigned long long) cache->bcull,
        //       (unsigned long long) cache->bstop,
        //       fnr, bnr);

        /* find out how many pages of blockdev are available */
        memset(&stats, 0, sizeof(stats));

        ret = vfs_statfs(&path, &stats);
        if (ret < 0) {
                trace_cachefiles_vfs_error(NULL, d_inode(path.dentry), ret,
                                           cachefiles_trace_statfs_error);
                if (ret == -EIO)
                        cachefiles_io_error(cache, "statfs failed");
                _leave(" = %d", ret);
                return ret;
        }

        b_avail = stats.f_bavail;
        b_writing = atomic_long_read(&cache->b_writing);
        if (b_avail > b_writing)
                b_avail -= b_writing;
        else
                b_avail = 0;

        //_debug("avail %llu,%llu",
        //       (unsigned long long)stats.f_ffree,
        //       (unsigned long long)b_avail);

        /* see if there is sufficient space */
        if (stats.f_ffree > fnr)
                stats.f_ffree -= fnr;
        else
                stats.f_ffree = 0;

        if (b_avail > bnr)
                b_avail -= bnr;
        else
                b_avail = 0;

        ret = -ENOBUFS;
        if (stats.f_ffree < cache->fstop ||
            b_avail < cache->bstop)
                goto stop_and_begin_cull;

        ret = 0;
        if (stats.f_ffree < cache->fcull ||
            b_avail < cache->bcull)
                goto begin_cull;

        if (test_bit(CACHEFILES_CULLING, &cache->flags) &&
            stats.f_ffree >= cache->frun &&
            b_avail >= cache->brun &&
            test_and_clear_bit(CACHEFILES_CULLING, &cache->flags)
            ) {
                _debug("cease culling");
                cachefiles_state_changed(cache);
        }

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

stop_and_begin_cull:
        switch (reason) {
        case cachefiles_has_space_for_write:
                fscache_count_no_write_space();
                break;
        case cachefiles_has_space_for_create:
                fscache_count_no_create_space();
                break;
        default:
                break;
        }
begin_cull:
        if (!test_and_set_bit(CACHEFILES_CULLING, &cache->flags)) {
                _debug("### CULL CACHE ###");
                cachefiles_state_changed(cache);
        }

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

/*
 * Mark all the objects as being out of service and queue them all for cleanup.
 */
static void cachefiles_withdraw_objects(struct cachefiles_cache *cache)
{
        struct cachefiles_object *object;
        unsigned int count = 0;

        _enter("");

        spin_lock(&cache->object_list_lock);

        while (!list_empty(&cache->object_list)) {
                object = list_first_entry(&cache->object_list,
                                          struct cachefiles_object, cache_link);
                cachefiles_see_object(object, cachefiles_obj_see_withdrawal);
                list_del_init(&object->cache_link);
                fscache_withdraw_cookie(object->cookie);
                count++;
                if ((count & 63) == 0) {
                        spin_unlock(&cache->object_list_lock);
                        cond_resched();
                        spin_lock(&cache->object_list_lock);
                }
        }

        spin_unlock(&cache->object_list_lock);
        _leave(" [%u objs]", count);
}

/*
 * Withdraw volumes.
 */
static void cachefiles_withdraw_volumes(struct cachefiles_cache *cache)
{
        _enter("");

        for (;;) {
                struct cachefiles_volume *volume = NULL;

                spin_lock(&cache->object_list_lock);
                if (!list_empty(&cache->volumes)) {
                        volume = list_first_entry(&cache->volumes,
                                                  struct cachefiles_volume, cache_link);
                        list_del_init(&volume->cache_link);
                }
                spin_unlock(&cache->object_list_lock);
                if (!volume)
                        break;

                cachefiles_withdraw_volume(volume);
        }

        _leave("");
}

/*
 * Sync a cache to backing disk.
 */
static void cachefiles_sync_cache(struct cachefiles_cache *cache)
{
        const struct cred *saved_cred;
        int ret;

        _enter("%s", cache->cache->name);

        /* 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);
}

/*
 * Withdraw cache objects.
 */
void cachefiles_withdraw_cache(struct cachefiles_cache *cache)
{
        struct fscache_cache *fscache = cache->cache;

        pr_info("File cache on %s unregistering\n", fscache->name);

        fscache_withdraw_cache(fscache);

        /* we now have to destroy all the active objects pertaining to this
         * cache - which we do by passing them off to thread pool to be
         * disposed of */
        cachefiles_withdraw_objects(cache);
        fscache_wait_for_objects(fscache);

        cachefiles_withdraw_volumes(cache);
        cachefiles_sync_cache(cache);
        cache->cache = NULL;
        fscache_relinquish_cache(fscache);
}