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1.1 root 1: /*
2: * linux/fs/msdos/fat.c
3: *
4: * Written 1992 by Werner Almesberger
5: */
6:
7: #include <linux/msdos_fs.h>
8: #include <linux/kernel.h>
9: #include <linux/errno.h>
10: #include <linux/stat.h>
11:
12: static struct fat_cache *fat_cache,cache[FAT_CACHE];
13:
14: /* Returns the this'th FAT entry, -1 if it is an end-of-file entry. If
15: new_value is != -1, that FAT entry is replaced by it. */
16:
17: int fat_access(struct super_block *sb,int this,int new_value)
18: {
19: struct buffer_head *bh,*bh2,*c_bh,*c_bh2;
20: unsigned char *p_first,*p_last;
21: void *data,*data2,*c_data,*c_data2;
22: int first,last,next,copy;
23:
24: if (MSDOS_SB(sb)->fat_bits == 16) first = last = this*2;
25: else {
26: first = this*3/2;
27: last = first+1;
28: }
29: if (!(bh = msdos_sread(sb->s_dev,MSDOS_SB(sb)->fat_start+(first >>
30: SECTOR_BITS),&data))) {
31: printk("bread in fat_access failed\r\n");
32: return 0;
33: }
34: if ((first >> SECTOR_BITS) == (last >> SECTOR_BITS)) {
35: bh2 = bh;
36: data2 = data;
37: }
38: else {
39: if (!(bh2 = msdos_sread(sb->s_dev,MSDOS_SB(sb)->fat_start+(last
40: >> SECTOR_BITS),&data2))) {
41: brelse(bh);
42: printk("bread in fat_access failed\r\n");
43: return 0;
44: }
45: }
46: if (MSDOS_SB(sb)->fat_bits == 16) {
47: next = ((unsigned short *) data)[(first & (SECTOR_SIZE-1))
48: >> 1];
49: if (next >= 0xfff8) next = -1;
50: }
51: else {
52: p_first = &((unsigned char *) data)[first & (SECTOR_SIZE-1)];
53: p_last = &((unsigned char *) data2)[(first+1) &
54: (SECTOR_SIZE-1)];
55: if (this & 1) next = ((*p_first >> 4) | (*p_last << 4)) & 0xfff;
56: else next = (*p_first+(*p_last << 8)) & 0xfff;
57: if (next >= 0xff8) next = -1;
58: }
59: if (new_value != -1) {
60: if (MSDOS_SB(sb)->fat_bits == 16)
61: ((unsigned short *) data)[(first & (SECTOR_SIZE-1)) >>
62: 1] = new_value;
63: else {
64: if (this & 1) {
65: *p_first = (*p_first & 0xf) | (new_value << 4);
66: *p_last = new_value >> 4;
67: }
68: else {
69: *p_first = new_value & 0xff;
70: *p_last = (*p_last & 0xf0) | (new_value >> 8);
71: }
72: bh2->b_dirt = 1;
73: }
74: bh->b_dirt = 1;
75: for (copy = 1; copy < MSDOS_SB(sb)->fats; copy++) {
76: if (!(c_bh = msdos_sread(sb->s_dev,MSDOS_SB(sb)->
77: fat_start+(first >> SECTOR_BITS)+MSDOS_SB(sb)->
78: fat_length*copy,&c_data))) break;
79: memcpy(c_data,data,SECTOR_SIZE);
80: c_bh->b_dirt = 1;
81: if (data != data2 || bh != bh2) {
82: if (!(c_bh2 = msdos_sread(sb->s_dev,
83: MSDOS_SB(sb)->fat_start+(first >>
84: SECTOR_BITS)+MSDOS_SB(sb)->fat_length*copy
85: +1,&c_data2))) {
86: brelse(c_bh);
87: break;
88: }
89: memcpy(c_data2,data2,SECTOR_SIZE);
90: brelse(c_bh2);
91: }
92: brelse(c_bh);
93: }
94: }
95: brelse(bh);
96: if (data != data2) brelse(bh2);
97: return next;
98: }
99:
100:
101: void cache_init(void)
102: {
103: static int initialized = 0;
104: int count;
105:
106: if (initialized) return;
107: fat_cache = &cache[0];
108: for (count = 0; count < FAT_CACHE; count++) {
109: cache[count].device = 0;
110: cache[count].next = count == FAT_CACHE-1 ? NULL :
111: &cache[count+1];
112: }
113: initialized = 1;
114: }
115:
116:
117: void cache_lookup(struct inode *inode,int cluster,int *f_clu,int *d_clu)
118: {
119: struct fat_cache *walk;
120:
121: #ifdef DEBUG
122: printk("cache lookup: %d\r\n",*f_clu);
123: #endif
124: for (walk = fat_cache; walk; walk = walk->next)
125: if (inode->i_dev == walk->device && walk->ino == inode->i_ino &&
126: walk->file_cluster <= cluster && walk->file_cluster >
127: *f_clu) {
128: *d_clu = walk->disk_cluster;
129: #ifdef DEBUG
130: printk("cache hit: %d (%d)\r\n",walk->file_cluster,*d_clu);
131: #endif
132: if ((*f_clu = walk->file_cluster) == cluster) return;
133: }
134: }
135:
136:
137: #ifdef DEBUG
138: static void list_cache(void)
139: {
140: struct fat_cache *walk;
141:
142: for (walk = fat_cache; walk; walk = walk->next) {
143: if (walk->device) printk("(%d,%d) ",walk->file_cluster,
144: walk->disk_cluster);
145: else printk("-- ");
146: }
147: printk("\r\n");
148: }
149: #endif
150:
151:
152: void cache_add(struct inode *inode,int f_clu,int d_clu)
153: {
154: struct fat_cache *walk,*last;
155:
156: #ifdef DEBUG
157: printk("cache add: %d (%d)\r\n",f_clu,d_clu);
158: #endif
159: last = NULL;
160: for (walk = fat_cache; walk->next; walk = (last = walk)->next)
161: if (inode->i_dev == walk->device && walk->ino == inode->i_ino &&
162: walk->file_cluster == f_clu) {
163: if (walk->disk_cluster != d_clu)
164: panic("FAT cache corruption");
165: /* update LRU */
166: if (last == NULL) return;
167: last->next = walk->next;
168: walk->next = fat_cache;
169: fat_cache = walk;
170: #ifdef DEBUG
171: list_cache();
172: #endif
173: return;
174: }
175: walk->device = inode->i_dev;
176: walk->ino = inode->i_ino;
177: walk->file_cluster = f_clu;
178: walk->disk_cluster = d_clu;
179: last->next = NULL;
180: walk->next = fat_cache;
181: fat_cache = walk;
182: #ifdef DEBUG
183: list_cache();
184: #endif
185: }
186:
187:
188: /* Cache invalidation occurs rarely, thus the LRU chain is not updated. It
189: fixes itself after a while. */
190:
191: void cache_inval_inode(struct inode *inode)
192: {
193: struct fat_cache *walk;
194:
195: for (walk = fat_cache; walk; walk = walk->next)
196: if (walk->device == inode->i_dev && walk->ino == inode->i_ino)
197: walk->device = 0;
198: }
199:
200:
201: void cache_inval_dev(int device)
202: {
203: struct fat_cache *walk;
204:
205: for (walk = fat_cache; walk; walk = walk->next)
206: if (walk->device == device) walk->device = 0;
207: }
208:
209:
210: int get_cluster(struct inode *inode,int cluster)
211: {
212: int this,count;
213:
214: if (!(this = inode->i_data[D_START])) return 0;
215: if (!cluster) return this;
216: count = 0;
217: for (cache_lookup(inode,cluster,&count,&this); count < cluster;
218: count++) {
219: if ((this = fat_access(inode->i_sb,this,-1)) == -1) return 0;
220: if (!this) return 0;
221: }
222: cache_add(inode,cluster,this);
223: return this;
224: }
225:
226:
227: int msdos_smap(struct inode *inode,int sector)
228: {
229: struct msdos_sb_info *sb;
230: int cluster,offset;
231:
232: sb = MSDOS_SB(inode->i_sb);
233: if (inode->i_ino == MSDOS_ROOT_INO || (S_ISDIR(inode->i_mode) &&
234: !inode->i_data[D_START])) {
235: if (sector >= sb->dir_entries >> MSDOS_DPS_BITS) return 0;
236: return sector+sb->dir_start;
237: }
238: cluster = sector/sb->cluster_size;
239: offset = sector % sb->cluster_size;
240: if (!(cluster = get_cluster(inode,cluster))) return 0;
241: return (cluster-2)*sb->cluster_size+sb->data_start+offset;
242: }
243:
244:
245: /* Free all clusters after the skip'th cluster. Doesn't use the cache,
246: because this way we get an additional sanity check. */
247:
248: int fat_free(struct inode *inode,int skip)
249: {
250: int this,last;
251:
252: if (!(this = inode->i_data[D_START])) return 0;
253: last = 0;
254: while (skip--) {
255: last = this;
256: if ((this = fat_access(inode->i_sb,this,-1)) == -1)
257: return 0;
258: if (!this) {
259: printk("fat_free: skipped EOF\r\n");
260: return -EIO;
261: }
262: }
263: if (last)
264: fat_access(inode->i_sb,last,MSDOS_SB(inode->i_sb)->fat_bits ==
265: 12 ? 0xff8 : 0xfff8);
266: else {
267: inode->i_data[D_START] = 0;
268: inode->i_dirt = 1;
269: }
270: while (this != -1)
271: if (!(this = fat_access(inode->i_sb,this,0)))
272: panic("fat_free: deleting beyond EOF");
273: cache_inval_inode(inode);
274: return 0;
275: }
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