[PATCH] hfs: don't reference missing page
[linux-2.6.git] / fs / hfs / part_tbl.c
1 /*
2  *  linux/fs/hfs/part_tbl.c
3  *
4  * Copyright (C) 1996-1997  Paul H. Hargrove
5  * (C) 2003 Ardis Technologies <roman@ardistech.com>
6  * This file may be distributed under the terms of the GNU General Public License.
7  *
8  * Original code to handle the new style Mac partition table based on
9  * a patch contributed by Holger Schemel (aeglos@valinor.owl.de).
10  */
11
12 #include "hfs_fs.h"
13
14 /*
15  * The new style Mac partition map
16  *
17  * For each partition on the media there is a physical block (512-byte
18  * block) containing one of these structures.  These blocks are
19  * contiguous starting at block 1.
20  */
21 struct new_pmap {
22         __be16  pmSig;          /* signature */
23         __be16  reSigPad;       /* padding */
24         __be32  pmMapBlkCnt;    /* partition blocks count */
25         __be32  pmPyPartStart;  /* physical block start of partition */
26         __be32  pmPartBlkCnt;   /* physical block count of partition */
27         u8      pmPartName[32]; /* (null terminated?) string
28                                    giving the name of this
29                                    partition */
30         u8      pmPartType[32]; /* (null terminated?) string
31                                    giving the type of this
32                                    partition */
33         /* a bunch more stuff we don't need */
34 } __packed;
35
36 /*
37  * The old style Mac partition map
38  *
39  * The partition map consists for a 2-byte signature followed by an
40  * array of these structures.  The map is terminated with an all-zero
41  * one of these.
42  */
43 struct old_pmap {
44         __be16          pdSig;  /* Signature bytes */
45         struct  old_pmap_entry {
46                 __be32  pdStart;
47                 __be32  pdSize;
48                 __be32  pdFSID;
49         }       pdEntry[42];
50 } __packed;
51
52 /*
53  * hfs_part_find()
54  *
55  * Parse the partition map looking for the
56  * start and length of the 'part'th HFS partition.
57  */
58 int hfs_part_find(struct super_block *sb,
59                   sector_t *part_start, sector_t *part_size)
60 {
61         struct buffer_head *bh;
62         __be16 *data;
63         int i, size, res;
64
65         res = -ENOENT;
66         bh = sb_bread512(sb, *part_start + HFS_PMAP_BLK, data);
67         if (!bh)
68                 return -EIO;
69
70         switch (be16_to_cpu(*data)) {
71         case HFS_OLD_PMAP_MAGIC:
72           {
73                 struct old_pmap *pm;
74                 struct old_pmap_entry *p;
75
76                 pm = (struct old_pmap *)bh->b_data;
77                 p = pm->pdEntry;
78                 size = 42;
79                 for (i = 0; i < size; p++, i++) {
80                         if (p->pdStart && p->pdSize &&
81                             p->pdFSID == cpu_to_be32(0x54465331)/*"TFS1"*/ &&
82                             (HFS_SB(sb)->part < 0 || HFS_SB(sb)->part == i)) {
83                                 *part_start += be32_to_cpu(p->pdStart);
84                                 *part_size = be32_to_cpu(p->pdSize);
85                                 res = 0;
86                         }
87                 }
88                 break;
89           }
90         case HFS_NEW_PMAP_MAGIC:
91           {
92                 struct new_pmap *pm;
93
94                 pm = (struct new_pmap *)bh->b_data;
95                 size = be32_to_cpu(pm->pmMapBlkCnt);
96                 for (i = 0; i < size;) {
97                         if (!memcmp(pm->pmPartType,"Apple_HFS", 9) &&
98                             (HFS_SB(sb)->part < 0 || HFS_SB(sb)->part == i)) {
99                                 *part_start += be32_to_cpu(pm->pmPyPartStart);
100                                 *part_size = be32_to_cpu(pm->pmPartBlkCnt);
101                                 res = 0;
102                                 break;
103                         }
104                         brelse(bh);
105                         bh = sb_bread512(sb, *part_start + HFS_PMAP_BLK + ++i, pm);
106                         if (!bh)
107                                 return -EIO;
108                         if (pm->pmSig != cpu_to_be16(HFS_NEW_PMAP_MAGIC))
109                                 break;
110                 }
111                 break;
112           }
113         }
114         brelse(bh);
115
116         return res;
117 }