/*
 * fs/logfs/inode.c     - inode handling code
 *
 * As should be obvious for Linux kernel code, license is GPLv2
 *
 * Copyright (c) 2005-2008 Joern Engel <joern@logfs.org>
 */
#include "logfs.h"
#include <linux/slab.h>
#include <linux/writeback.h>
#include <linux/backing-dev.h>

/*
 * How soon to reuse old inode numbers?  LogFS doesn't store deleted inodes
 * on the medium.  It therefore also lacks a method to store the previous
 * generation number for deleted inodes.  Instead a single generation number
 * is stored which will be used for new inodes.  Being just a 32bit counter,
 * this can obvious wrap relatively quickly.  So we only reuse inodes if we
 * know that a fair number of inodes can be created before we have to increment
 * the generation again - effectively adding some bits to the counter.
 * But being too aggressive here means we keep a very large and very sparse
 * inode file, wasting space on indirect blocks.
 * So what is a good value?  Beats me.  64k seems moderately bad on both
 * fronts, so let's use that for now...
 *
 * NFS sucks, as everyone already knows.
 */
#define INOS_PER_WRAP (0x10000)

/*
 * Logfs' requirement to read inodes for garbage collection makes life a bit
 * harder.  GC may have to read inodes that are in I_FREEING state, when they
 * are being written out - and waiting for GC to make progress, naturally.
 *
 * So we cannot just call iget() or some variant of it, but first have to check
 * whether the inode in question might be in I_FREEING state.  Therefore we
 * maintain our own per-sb list of "almost deleted" inodes and check against
 * that list first.  Normally this should be at most 1-2 entries long.
 *
 * Also, inodes have logfs-specific reference counting on top of what the vfs
 * does.  When .destroy_inode is called, normally the reference count will drop
 * to zero and the inode gets deleted.  But if GC accessed the inode, its
 * refcount will remain nonzero and final deletion will have to wait.
 *
 * As a result we have two sets of functions to get/put inodes:
 * logfs_safe_iget/logfs_safe_iput      - safe to call from GC context
 * logfs_iget/iput                      - normal version
 */
static struct kmem_cache *logfs_inode_cache;

static DEFINE_SPINLOCK(logfs_inode_lock);

static void logfs_inode_setops(struct inode *inode)
{
        switch (inode->i_mode & S_IFMT) {
        case S_IFDIR:
                inode->i_op = &logfs_dir_iops;
                inode->i_fop = &logfs_dir_fops;
                inode->i_mapping->a_ops = &logfs_reg_aops;
                break;
        case S_IFREG:
                inode->i_op = &logfs_reg_iops;
                inode->i_fop = &logfs_reg_fops;
                inode->i_mapping->a_ops = &logfs_reg_aops;
                break;
        case S_IFLNK:
                inode->i_op = &page_symlink_inode_operations;
                inode_nohighmem(inode);
                inode->i_mapping->a_ops = &logfs_reg_aops;
                break;
        case S_IFSOCK:  /* fall through */
        case S_IFBLK:   /* fall through */
        case S_IFCHR:   /* fall through */
        case S_IFIFO:
                init_special_inode(inode, inode->i_mode, inode->i_rdev);
                break;
        default:
                BUG();
        }
}

static struct inode *__logfs_iget(struct super_block *sb, ino_t ino)
{
        struct inode *inode = iget_locked(sb, ino);
        int err;

        if (!inode)
                return ERR_PTR(-ENOMEM);
        if (!(inode->i_state & I_NEW))
                return inode;

        err = logfs_read_inode(inode);
        if (err || inode->i_nlink == 0) {
                /* inode->i_nlink == 0 can be true when called from
                 * block validator */
                /* set i_nlink to 0 to prevent caching */
                clear_nlink(inode);
                logfs_inode(inode)->li_flags |= LOGFS_IF_ZOMBIE;
                iget_failed(inode);
                if (!err)
                        err = -ENOENT;
                return ERR_PTR(err);
        }

        logfs_inode_setops(inode);
        unlock_new_inode(inode);
        return inode;
}

struct inode *logfs_iget(struct super_block *sb, ino_t ino)
{
        BUG_ON(ino == LOGFS_INO_MASTER);
        BUG_ON(ino == LOGFS_INO_SEGFILE);
        return __logfs_iget(sb, ino);
}

/*
 * is_cached is set to 1 if we hand out a cached inode, 0 otherwise.
 * this allows logfs_iput to do the right thing later
 */
struct inode *logfs_safe_iget(struct super_block *sb, ino_t ino, int *is_cached)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_inode *li;

        if (ino == LOGFS_INO_MASTER)
                return super->s_master_inode;
        if (ino == LOGFS_INO_SEGFILE)
                return super->s_segfile_inode;

        spin_lock(&logfs_inode_lock);
        list_for_each_entry(li, &super->s_freeing_list, li_freeing_list)
                if (li->vfs_inode.i_ino == ino) {
                        li->li_refcount++;
                        spin_unlock(&logfs_inode_lock);
                        *is_cached = 1;
                        return &li->vfs_inode;
                }
        spin_unlock(&logfs_inode_lock);

        *is_cached = 0;
        return __logfs_iget(sb, ino);
}

static void logfs_i_callback(struct rcu_head *head)
{
        struct inode *inode = container_of(head, struct inode, i_rcu);
        kmem_cache_free(logfs_inode_cache, logfs_inode(inode));
}

static void __logfs_destroy_inode(struct inode *inode)
{
        struct logfs_inode *li = logfs_inode(inode);

        BUG_ON(li->li_block);
        list_del(&li->li_freeing_list);
        call_rcu(&inode->i_rcu, logfs_i_callback);
}

static void __logfs_destroy_meta_inode(struct inode *inode)
{
        struct logfs_inode *li = logfs_inode(inode);
        BUG_ON(li->li_block);
        call_rcu(&inode->i_rcu, logfs_i_callback);
}

static void logfs_destroy_inode(struct inode *inode)
{
        struct logfs_inode *li = logfs_inode(inode);

        if (inode->i_ino < LOGFS_RESERVED_INOS) {
                /*
                 * The reserved inodes are never destroyed unless we are in
                 * unmont path.
                 */
                __logfs_destroy_meta_inode(inode);
                return;
        }

        BUG_ON(list_empty(&li->li_freeing_list));
        spin_lock(&logfs_inode_lock);
        li->li_refcount--;
        if (li->li_refcount == 0)
                __logfs_destroy_inode(inode);
        spin_unlock(&logfs_inode_lock);
}

void logfs_safe_iput(struct inode *inode, int is_cached)
{
        if (inode->i_ino == LOGFS_INO_MASTER)
                return;
        if (inode->i_ino == LOGFS_INO_SEGFILE)
                return;

        if (is_cached) {
                logfs_destroy_inode(inode);
                return;
        }

        iput(inode);
}

static void logfs_init_inode(struct super_block *sb, struct inode *inode)
{
        struct logfs_inode *li = logfs_inode(inode);
        int i;

        li->li_flags    = 0;
        li->li_height   = 0;
        li->li_used_bytes = 0;
        li->li_block    = NULL;
        i_uid_write(inode, 0);
        i_gid_write(inode, 0);
        inode->i_size   = 0;
        inode->i_blocks = 0;
        inode->i_ctime  = CURRENT_TIME;
        inode->i_mtime  = CURRENT_TIME;
        li->li_refcount = 1;
        INIT_LIST_HEAD(&li->li_freeing_list);

        for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
                li->li_data[i] = 0;

        return;
}

static struct inode *logfs_alloc_inode(struct super_block *sb)
{
        struct logfs_inode *li;

        li = kmem_cache_alloc(logfs_inode_cache, GFP_NOFS);
        if (!li)
                return NULL;
        logfs_init_inode(sb, &li->vfs_inode);
        return &li->vfs_inode;
}

/*
 * In logfs inodes are written to an inode file.  The inode file, like any
 * other file, is managed with a inode.  The inode file's inode, aka master
 * inode, requires special handling in several respects.  First, it cannot be
 * written to the inode file, so it is stored in the journal instead.
 *
 * Secondly, this inode cannot be written back and destroyed before all other
 * inodes have been written.  The ordering is important.  Linux' VFS is happily
 * unaware of the ordering constraint and would ordinarily destroy the master
 * inode at umount time while other inodes are still in use and dirty.  Not
 * good.
 *
 * So logfs makes sure the master inode is not written until all other inodes
 * have been destroyed.  Sadly, this method has another side-effect.  The VFS
 * will notice one remaining inode and print a frightening warning message.
 * Worse, it is impossible to judge whether such a warning was caused by the
 * master inode or any other inodes have leaked as well.
 *
 * Our attempt of solving this is with logfs_new_meta_inode() below.  Its
 * purpose is to create a new inode that will not trigger the warning if such
 * an inode is still in use.  An ugly hack, no doubt.  Suggections for
 * improvement are welcome.
 *
 * AV: that's what ->put_super() is for...
 */
struct inode *logfs_new_meta_inode(struct super_block *sb, u64 ino)
{
        struct inode *inode;

        inode = new_inode(sb);
        if (!inode)
                return ERR_PTR(-ENOMEM);

        inode->i_mode = S_IFREG;
        inode->i_ino = ino;
        inode->i_data.a_ops = &logfs_reg_aops;
        mapping_set_gfp_mask(&inode->i_data, GFP_NOFS);

        return inode;
}

struct inode *logfs_read_meta_inode(struct super_block *sb, u64 ino)
{
        struct inode *inode;
        int err;

        inode = logfs_new_meta_inode(sb, ino);
        if (IS_ERR(inode))
                return inode;

        err = logfs_read_inode(inode);
        if (err) {
                iput(inode);
                return ERR_PTR(err);
        }
        logfs_inode_setops(inode);
        return inode;
}

static int logfs_write_inode(struct inode *inode, struct writeback_control *wbc)
{
        int ret;
        long flags = WF_LOCK;

        /* Can only happen if creat() failed.  Safe to skip. */
        if (logfs_inode(inode)->li_flags & LOGFS_IF_STILLBORN)
                return 0;

        ret = __logfs_write_inode(inode, NULL, flags);
        LOGFS_BUG_ON(ret, inode->i_sb);
        return ret;
}

/* called with inode->i_lock held */
static int logfs_drop_inode(struct inode *inode)
{
        struct logfs_super *super = logfs_super(inode->i_sb);
        struct logfs_inode *li = logfs_inode(inode);

        spin_lock(&logfs_inode_lock);
        list_move(&li->li_freeing_list, &super->s_freeing_list);
        spin_unlock(&logfs_inode_lock);
        return generic_drop_inode(inode);
}

static void logfs_set_ino_generation(struct super_block *sb,
                struct inode *inode)
{
        struct logfs_super *super = logfs_super(sb);
        u64 ino;

        mutex_lock(&super->s_journal_mutex);
        ino = logfs_seek_hole(super->s_master_inode, super->s_last_ino + 1);
        super->s_last_ino = ino;
        super->s_inos_till_wrap--;
        if (super->s_inos_till_wrap < 0) {
                super->s_last_ino = LOGFS_RESERVED_INOS;
                super->s_generation++;
                super->s_inos_till_wrap = INOS_PER_WRAP;
        }
        inode->i_ino = ino;
        inode->i_generation = super->s_generation;
        mutex_unlock(&super->s_journal_mutex);
}

struct inode *logfs_new_inode(struct inode *dir, umode_t mode)
{
        struct super_block *sb = dir->i_sb;
        struct inode *inode;

        inode = new_inode(sb);
        if (!inode)
                return ERR_PTR(-ENOMEM);

        logfs_init_inode(sb, inode);

        /* inherit parent flags */
        logfs_inode(inode)->li_flags |=
                logfs_inode(dir)->li_flags & LOGFS_FL_INHERITED;

        inode->i_mode = mode;
        logfs_set_ino_generation(sb, inode);

        inode_init_owner(inode, dir, mode);
        logfs_inode_setops(inode);
        insert_inode_hash(inode);

        return inode;
}

static void logfs_init_once(void *_li)
{
        struct logfs_inode *li = _li;
        int i;

        li->li_flags = 0;
        li->li_used_bytes = 0;
        li->li_refcount = 1;
        for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
                li->li_data[i] = 0;
        inode_init_once(&li->vfs_inode);
}

static int logfs_sync_fs(struct super_block *sb, int wait)
{
        logfs_get_wblocks(sb, NULL, WF_LOCK);
        logfs_write_anchor(sb);
        logfs_put_wblocks(sb, NULL, WF_LOCK);
        return 0;
}

static void logfs_put_super(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        /* kill the meta-inodes */
        iput(super->s_segfile_inode);
        iput(super->s_master_inode);
        iput(super->s_mapping_inode);
}

const struct super_operations logfs_super_operations = {
        .alloc_inode    = logfs_alloc_inode,
        .destroy_inode  = logfs_destroy_inode,
        .evict_inode    = logfs_evict_inode,
        .drop_inode     = logfs_drop_inode,
        .put_super      = logfs_put_super,
        .write_inode    = logfs_write_inode,
        .statfs         = logfs_statfs,
        .sync_fs        = logfs_sync_fs,
};

int logfs_init_inode_cache(void)
{
        logfs_inode_cache = kmem_cache_create("logfs_inode_cache",
                        sizeof(struct logfs_inode), 0,
                        SLAB_RECLAIM_ACCOUNT|SLAB_ACCOUNT,
                        logfs_init_once);
        if (!logfs_inode_cache)
                return -ENOMEM;
        return 0;
}

void logfs_destroy_inode_cache(void)
{
        /*
         * Make sure all delayed rcu free inodes are flushed before we
         * destroy cache.
         */
        rcu_barrier();
        kmem_cache_destroy(logfs_inode_cache);
}