xref: /openbmc/linux/fs/squashfs/id.c (revision 4800cd83)
1 /*
2  * Squashfs - a compressed read only filesystem for Linux
3  *
4  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
5  * Phillip Lougher <phillip@lougher.demon.co.uk>
6  *
7  * This program is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU General Public License
9  * as published by the Free Software Foundation; either version 2,
10  * or (at your option) any later version.
11  *
12  * This program is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15  * GNU General Public License for more details.
16  *
17  * You should have received a copy of the GNU General Public License
18  * along with this program; if not, write to the Free Software
19  * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
20  *
21  * id.c
22  */
23 
24 /*
25  * This file implements code to handle uids and gids.
26  *
27  * For space efficiency regular files store uid and gid indexes, which are
28  * converted to 32-bit uids/gids using an id look up table.  This table is
29  * stored compressed into metadata blocks.  A second index table is used to
30  * locate these.  This second index table for speed of access (and because it
31  * is small) is read at mount time and cached in memory.
32  */
33 
34 #include <linux/fs.h>
35 #include <linux/vfs.h>
36 #include <linux/slab.h>
37 
38 #include "squashfs_fs.h"
39 #include "squashfs_fs_sb.h"
40 #include "squashfs.h"
41 
42 /*
43  * Map uid/gid index into real 32-bit uid/gid using the id look up table
44  */
45 int squashfs_get_id(struct super_block *sb, unsigned int index,
46 					unsigned int *id)
47 {
48 	struct squashfs_sb_info *msblk = sb->s_fs_info;
49 	int block = SQUASHFS_ID_BLOCK(index);
50 	int offset = SQUASHFS_ID_BLOCK_OFFSET(index);
51 	u64 start_block = le64_to_cpu(msblk->id_table[block]);
52 	__le32 disk_id;
53 	int err;
54 
55 	err = squashfs_read_metadata(sb, &disk_id, &start_block, &offset,
56 							sizeof(disk_id));
57 	if (err < 0)
58 		return err;
59 
60 	*id = le32_to_cpu(disk_id);
61 	return 0;
62 }
63 
64 
65 /*
66  * Read uncompressed id lookup table indexes from disk into memory
67  */
68 __le64 *squashfs_read_id_index_table(struct super_block *sb,
69 			u64 id_table_start, unsigned short no_ids)
70 {
71 	unsigned int length = SQUASHFS_ID_BLOCK_BYTES(no_ids);
72 	__le64 *id_table;
73 	int err;
74 
75 	TRACE("In read_id_index_table, length %d\n", length);
76 
77 	/* Allocate id lookup table indexes */
78 	id_table = kmalloc(length, GFP_KERNEL);
79 	if (id_table == NULL) {
80 		ERROR("Failed to allocate id index table\n");
81 		return ERR_PTR(-ENOMEM);
82 	}
83 
84 	err = squashfs_read_table(sb, id_table, id_table_start, length);
85 	if (err < 0) {
86 		ERROR("unable to read id index table\n");
87 		kfree(id_table);
88 		return ERR_PTR(err);
89 	}
90 
91 	return id_table;
92 }
93