/*
 * 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);
}