/*
 * Copyright (c) 2012 Dave Vasilevsky <dave@vasilevsky.ca>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
#include "ll.h"

#include "hash.h"
#include "nonstd.h"

#include <errno.h>
#include <stdlib.h>
#include <string.h>

/*

We have three kinds of unique identifiers for inodes:

1. sqfs_inode_id
  - Points directly to the on-disk location of the inode data.
  - A 48-bit integer (32-bit block id, and 16 bit offset within a block).
  - Not assigned sequentially, two IDs will differ by at least 20.
  - The root inode may have any value of sqfs_inode_id.
  - You CAN easily get the inode data from an sqfs_inode_id.
  - You CANNOT get the sqfs_inode_id from the inode data.

2. sqfs_inode_number
  - Arbitrary identifier for inodes, assigned by mksquashfs.
  - A 32-bit integer.
  - Assigned sequentially, starting at zero.
  - The root inode generally has the value zero.
  - You CANNOT find the inode data directly from an sqfs_inode_number.
  - You CAN find the sqfs_inode_number from the inode data.
  - You CAN lookup sqfs_inode_number -> sqfs_inode_id IFF the squashfs
    archive has the optional export table enabled.

3. fuse_ino_t
  - Arbitrary identifier for inodes, assigned by the FUSE driver.
  - Has the same width as 'long', either 32- or 64-bit.
  - The value zero is reserved to indicate a non-existent entry.
  - The value one is reserved to indicate the root inode.


To implement a low-level filesystem, we must:
  - Generate a fuse_ino_t when telling FUSE about a new inode.
  - Find the inode data when FUSE asks us about a fuse_ino_t.

So we need a bidirectional mapping between fuse_ino_t and sqfs_inode_id.
We use several different strategies, depending on the bitness of the system,
and whether or not the squashfs archive has an export table:

1. On 64-bit systems: fuse_ino_t is big enough to hold the sqfs_inode_id.
	 We can just make minor adjustments for the reserved values of fuse_ino_t.

2. On 32-bit systems, with export table: fuse_ino_t can hold the
	 sqfs_inode_number, with adjustments for reserved values. We can use the
   export table to lookup the sqfs_inode_id from the sqfs_inode_number.

3. On 32-bit systems, no export: fuse_ino_t again holds sqfs_inode_number.
   But we have to maintain our own mapping of
	 sqfs_inode_number -> sqfs_inode_id, which can use quite a lot of memory.

*/


/***** INODE CONVERSION FOR 64-BIT INODES ****
 *
 * sqfs(root) maps to FUSE_ROOT_ID == 1
 * sqfs(0) maps to 2
 *
 * Both 1 and 2 are guaranteed not to be used by sqfs, due to inode size
 */
static fuse_ino_t sqfs_ll_ino64_fuse(sqfs_ll *ll, sqfs_inode_id i) {
	if (i == sqfs_inode_root(&ll->fs)) {
		return FUSE_ROOT_ID;
	} else if (i == 0) {
		return 2;
	} else {
		return i;
	}
}

static sqfs_inode_id sqfs_ll_ino64_sqfs(sqfs_ll *ll, fuse_ino_t i) {
	if (i == FUSE_ROOT_ID) {
		return sqfs_inode_root(&ll->fs);
	} else if (i == 2) {
		return 0;
	} else {
		return i;
	}
}

static fuse_ino_t sqfs_ll_ino64_fuse_num(sqfs_ll *ll, sqfs_dir_entry *e) {
	return sqfs_ll_ino64_fuse(ll, sqfs_dentry_inode(e));
}

static sqfs_err sqfs_ll_ino64_init(sqfs_ll *ll) {
	ll->ino_fuse = sqfs_ll_ino64_fuse;
	ll->ino_sqfs = sqfs_ll_ino64_sqfs;
	ll->ino_fuse_num = sqfs_ll_ino64_fuse_num;
	return SQFS_OK;
}



/***** INODE CONVERSION FOR 32-BIT INODES ****
 *
 * We maintain a cache of sqfs_inode_num => sqfs_inode_id.
 * We go the other direction by fetching inodes.
 *
 * Mapping: sqfs_inode_num <=> fuse_ino_t
 *   Most num(N) maps to N + 1
 *   num(root) maps to FUSE_ROOT_ID == 1
 *   num(0) maps to num(root) + 1
 *
 * FIXME:
 * - Theoretically this could overflow if a filesystem uses all 2 ** 32 inodes,
 *   since fuse inode zero is unavailable.
 */
#define SQFS_ICACHE_INITIAL 32

#define FUSE_INODE_NONE 0
#define SQFS_INODE_NONE 1

typedef struct {
	sqfs_inode_num root;
	sqfs_hash icache;
} sqfs_ll_inode_map;

/* Pack tightly to save memory */
typedef struct {
	uint32_t refcount;
	uint32_t ino_hi;
	uint16_t ino_lo;
} sqfs_ll_inode_entry;

#define IE_INODE(ie) (((uint64_t)(ie)->ino_hi << 16) | (ie)->ino_lo)
#define INODE_HI(i) ((i) >> 16)
#define INODE_LO(i) ((i) & 0xFFFF)

static fuse_ino_t sqfs_ll_ino32_num2fuse(sqfs_ll *ll, sqfs_inode_num n) {
	sqfs_ll_inode_map *map = ll->ino_data;
	if (n == map->root) {
		return FUSE_ROOT_ID;
	} else if (n == 0) {
		return map->root + 1;
	} else {
		return n + 1;
	} 
}

static fuse_ino_t sqfs_ll_ino32_fuse2num(sqfs_ll *ll, fuse_ino_t i) {
	sqfs_ll_inode_map *map = ll->ino_data;
	if (i == FUSE_ROOT_ID) {
		return map->root;
	} else if (i == map->root + 1) {
		return 0;
	} else {
		return i - 1;
	}
}

static fuse_ino_t sqfs_ll_ino32_fuse(sqfs_ll *ll, sqfs_inode_id i) {
	sqfs_inode inode;
	if (sqfs_inode_get(&ll->fs, &inode, i))
		return FUSE_INODE_NONE; /* We shouldn't get here! */
	return sqfs_ll_ino32_num2fuse(ll, inode.base.inode_number);
}

static sqfs_inode_id sqfs_ll_ino32_sqfs(sqfs_ll *ll, fuse_ino_t i) {
	sqfs_ll_inode_map *map;
	sqfs_inode_num n;
	sqfs_ll_inode_entry *ie;
	
	if (i == FUSE_ROOT_ID)
		return sqfs_inode_root(&ll->fs);
	
	map = ll->ino_data;
	n = sqfs_ll_ino32_fuse2num(ll, i);
	
	ie = sqfs_hash_get(&map->icache, n);
	return ie ? IE_INODE(ie) : SQFS_INODE_NONE;
}

static fuse_ino_t sqfs_ll_ino32_fuse_num(sqfs_ll *ll, sqfs_dir_entry *e) {
	return sqfs_ll_ino32_num2fuse(ll, sqfs_dentry_inode_num(e));
}

static fuse_ino_t sqfs_ll_ino32_register(sqfs_ll *ll, sqfs_dir_entry *e) {
	sqfs_ll_inode_map *map = ll->ino_data;
	
	sqfs_ll_inode_entry *ie = sqfs_hash_get(&map->icache,
		sqfs_dentry_inode_num(e));
	if (ie) {
		++ie->refcount;
	} else {
		sqfs_err err = SQFS_OK;
		sqfs_inode_id i = sqfs_dentry_inode(e);
		sqfs_ll_inode_entry nie;
		nie.ino_hi = INODE_HI(i);
		nie.ino_lo = INODE_LO(i);
		nie.refcount = 1;
		err = sqfs_hash_add(&map->icache, sqfs_dentry_inode_num(e), &nie);
		if (err)
			return FUSE_INODE_NONE;
	}
	
	return sqfs_ll_ino32_fuse_num(ll, e);
}

static void sqfs_ll_ino32_forget(sqfs_ll *ll, fuse_ino_t i, size_t refs) {
	sqfs_ll_inode_map *map = ll->ino_data;
	sqfs_inode_num n = sqfs_ll_ino32_fuse2num(ll, i);
	
	sqfs_ll_inode_entry *ie = sqfs_hash_get(&map->icache, n);
	if (!ie)
		return;
	
	if (ie->refcount > refs) {
		ie->refcount -= refs;
	} else {
		sqfs_hash_remove(&map->icache, n);
	}
}

static void sqfs_ll_ino32_destroy(sqfs_ll *ll) {
	sqfs_ll_inode_map *map = ll->ino_data;
	sqfs_hash_destroy(&map->icache);
	free(map);
}

static sqfs_err sqfs_ll_ino32_init(sqfs_ll *ll) {
	sqfs_inode inode;
	sqfs_ll_inode_map *map;
	sqfs_err err = sqfs_inode_get(&ll->fs, &inode, sqfs_inode_root(&ll->fs));
	if (err)
		return err;
		
	map = malloc(sizeof(sqfs_ll_inode_map));
	map->root = inode.base.inode_number;
	sqfs_hash_init(&map->icache, sizeof(sqfs_ll_inode_entry),
		SQFS_ICACHE_INITIAL);
		
	ll->ino_fuse = sqfs_ll_ino32_fuse;
	ll->ino_sqfs = sqfs_ll_ino32_sqfs;
	ll->ino_fuse_num = sqfs_ll_ino32_fuse_num;
	ll->ino_register = sqfs_ll_ino32_register;
	ll->ino_forget = sqfs_ll_ino32_forget;
	ll->ino_destroy = sqfs_ll_ino32_destroy;
	ll->ino_data = map;
	
	return err; 
}



/***** INODE CONVERSION FOR 32-BIT INODES, EXPORT TABLE AVAILABLE ****
 *
 * Same transformation as regular 32-bit, but no caching.
 */
static sqfs_inode_id sqfs_ll_ino32exp_sqfs(sqfs_ll *ll, fuse_ino_t i) {
	sqfs_inode_num n;
	sqfs_inode_id ret;
	sqfs_err err = SQFS_OK;
	
	if (i == FUSE_ROOT_ID)
		return sqfs_inode_root(&ll->fs);
	
	n = sqfs_ll_ino32_fuse2num(ll, i);
	err = sqfs_export_inode(&ll->fs, n, &ret);
	return err ? SQFS_INODE_NONE : ret;
}

static void sqfs_ll_ino32exp_destroy(sqfs_ll *ll) {
	free(ll->ino_data);
}

static sqfs_err sqfs_ll_ino32exp_init(sqfs_ll *ll) {
	sqfs_inode inode;
	sqfs_ll_inode_map *map;
	sqfs_err err = sqfs_inode_get(&ll->fs, &inode, sqfs_inode_root(&ll->fs));
	if (err)
		return err;
		
	map = malloc(sizeof(sqfs_ll_inode_map));
	map->root = inode.base.inode_number;
	
	ll->ino_fuse = sqfs_ll_ino32_fuse;
	ll->ino_sqfs = sqfs_ll_ino32exp_sqfs;
	ll->ino_fuse_num = sqfs_ll_ino32_fuse_num;
	ll->ino_destroy = sqfs_ll_ino32exp_destroy;
	ll->ino_data = map;
	
	return err;
}



static void sqfs_ll_null_forget(sqfs_ll *ll, fuse_ino_t i, size_t refs) {
	/* pass */
}

sqfs_err sqfs_ll_init(sqfs_ll *ll) {
	sqfs_err err = SQFS_OK;	
	if (sizeof(fuse_ino_t) >= SQFS_INODE_ID_BYTES) {
		err = sqfs_ll_ino64_init(ll);
	} else if (sqfs_export_ok(&ll->fs)) {
		err = sqfs_ll_ino32exp_init(ll);
	} else {
		err = sqfs_ll_ino32_init(ll);
	}
	if (!ll->ino_register)
		ll->ino_register = ll->ino_fuse_num;
	if (!ll->ino_forget)
		ll->ino_forget = sqfs_ll_null_forget;
	
	return err;
}

void sqfs_ll_destroy(sqfs_ll *ll) {
	sqfs_destroy(&ll->fs);
	if (ll->ino_destroy)
		ll->ino_destroy(ll);
}

sqfs_err sqfs_ll_inode(sqfs_ll *ll, sqfs_inode *inode, fuse_ino_t i) {
	return sqfs_inode_get(&ll->fs, inode, ll->ino_sqfs(ll, i));
}


sqfs_err sqfs_ll_iget(fuse_req_t req, sqfs_ll_i *lli, fuse_ino_t i) {
	sqfs_err err = SQFS_OK;
	lli->ll = fuse_req_userdata(req);
	if (i != SQFS_FUSE_INODE_NONE) {
		err = sqfs_ll_inode(lli->ll, &lli->inode, i);
		if (err)
			fuse_reply_err(req, ENOENT);
	}
	return err;
}

sqfs_err sqfs_ll_stat(sqfs_ll *ll, sqfs_inode *inode, struct stat *st) {
	sqfs_err err = SQFS_OK;
	uid_t id;
	
	memset(st, 0, sizeof(*st));
	st->st_mode = inode->base.mode;
	st->st_nlink = inode->nlink;
	st->st_mtime = st->st_ctime = st->st_atime = inode->base.mtime;
	
	if (S_ISREG(st->st_mode)) {
		/* FIXME: do symlinks, dirs, etc have a size? */
		st->st_size = inode->xtra.reg.file_size;
		st->st_blocks = st->st_size / 512;
	} else if (S_ISBLK(st->st_mode) || S_ISCHR(st->st_mode)) {
		st->st_rdev = sqfs_makedev(inode->xtra.dev.major,
			inode->xtra.dev.minor);
	}
	
	st->st_blksize = ll->fs.sb.block_size; /* seriously? */
	
	err = sqfs_id_get(&ll->fs, inode->base.uid, &id);
	if (err)
		return err;
	st->st_uid = id;
	err = sqfs_id_get(&ll->fs, inode->base.guid, &id);
	st->st_gid = id;
	if (err)
		return err;
	
	return SQFS_OK;
}