Annotation of qemu/block-cow.c, revision 1.1.1.2
1.1 root 1: /*
2: * Block driver for the COW format
3: *
4: * Copyright (c) 2004 Fabrice Bellard
5: *
6: * Permission is hereby granted, free of charge, to any person obtaining a copy
7: * of this software and associated documentation files (the "Software"), to deal
8: * in the Software without restriction, including without limitation the rights
9: * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10: * copies of the Software, and to permit persons to whom the Software is
11: * furnished to do so, subject to the following conditions:
12: *
13: * The above copyright notice and this permission notice shall be included in
14: * all copies or substantial portions of the Software.
15: *
16: * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17: * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18: * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19: * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20: * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21: * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
22: * THE SOFTWARE.
23: */
24: #ifndef _WIN32
25: #include "vl.h"
26: #include "block_int.h"
27: #include <sys/mman.h>
28:
29: /**************************************************************/
30: /* COW block driver using file system holes */
31:
32: /* user mode linux compatible COW file */
33: #define COW_MAGIC 0x4f4f4f4d /* MOOO */
34: #define COW_VERSION 2
35:
36: struct cow_header_v2 {
37: uint32_t magic;
38: uint32_t version;
39: char backing_file[1024];
40: int32_t mtime;
41: uint64_t size;
42: uint32_t sectorsize;
43: };
44:
45: typedef struct BDRVCowState {
46: int fd;
47: uint8_t *cow_bitmap; /* if non NULL, COW mappings are used first */
48: uint8_t *cow_bitmap_addr; /* mmap address of cow_bitmap */
49: int cow_bitmap_size;
50: int64_t cow_sectors_offset;
51: } BDRVCowState;
52:
53: static int cow_probe(const uint8_t *buf, int buf_size, const char *filename)
54: {
55: const struct cow_header_v2 *cow_header = (const void *)buf;
56:
57: if (buf_size >= sizeof(struct cow_header_v2) &&
58: be32_to_cpu(cow_header->magic) == COW_MAGIC &&
59: be32_to_cpu(cow_header->version) == COW_VERSION)
60: return 100;
61: else
62: return 0;
63: }
64:
65: static int cow_open(BlockDriverState *bs, const char *filename)
66: {
67: BDRVCowState *s = bs->opaque;
68: int fd;
69: struct cow_header_v2 cow_header;
70: int64_t size;
71:
72: fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);
73: if (fd < 0) {
74: fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
75: if (fd < 0)
76: return -1;
77: }
78: s->fd = fd;
79: /* see if it is a cow image */
80: if (read(fd, &cow_header, sizeof(cow_header)) != sizeof(cow_header)) {
81: goto fail;
82: }
83:
84: if (be32_to_cpu(cow_header.magic) != COW_MAGIC ||
85: be32_to_cpu(cow_header.version) != COW_VERSION) {
86: goto fail;
87: }
88:
89: /* cow image found */
90: size = be64_to_cpu(cow_header.size);
91: bs->total_sectors = size / 512;
92:
93: pstrcpy(bs->backing_file, sizeof(bs->backing_file),
94: cow_header.backing_file);
95:
96: #if 0
97: if (cow_header.backing_file[0] != '\0') {
98: if (stat(cow_header.backing_file, &st) != 0) {
99: fprintf(stderr, "%s: could not find original disk image '%s'\n", filename, cow_header.backing_file);
100: goto fail;
101: }
102: if (st.st_mtime != be32_to_cpu(cow_header.mtime)) {
103: fprintf(stderr, "%s: original raw disk image '%s' does not match saved timestamp\n", filename, cow_header.backing_file);
104: goto fail;
105: }
106: fd = open(cow_header.backing_file, O_RDONLY | O_LARGEFILE);
107: if (fd < 0)
108: goto fail;
109: bs->fd = fd;
110: }
111: #endif
112: /* mmap the bitmap */
113: s->cow_bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
114: s->cow_bitmap_addr = mmap(get_mmap_addr(s->cow_bitmap_size),
115: s->cow_bitmap_size,
116: PROT_READ | PROT_WRITE,
117: MAP_SHARED, s->fd, 0);
118: if (s->cow_bitmap_addr == MAP_FAILED)
119: goto fail;
120: s->cow_bitmap = s->cow_bitmap_addr + sizeof(cow_header);
121: s->cow_sectors_offset = (s->cow_bitmap_size + 511) & ~511;
122: return 0;
123: fail:
124: close(fd);
125: return -1;
126: }
127:
128: static inline void cow_set_bit(uint8_t *bitmap, int64_t bitnum)
129: {
130: bitmap[bitnum / 8] |= (1 << (bitnum%8));
131: }
132:
133: static inline int is_bit_set(const uint8_t *bitmap, int64_t bitnum)
134: {
135: return !!(bitmap[bitnum / 8] & (1 << (bitnum%8)));
136: }
137:
138:
139: /* Return true if first block has been changed (ie. current version is
140: * in COW file). Set the number of continuous blocks for which that
141: * is true. */
142: static inline int is_changed(uint8_t *bitmap,
143: int64_t sector_num, int nb_sectors,
144: int *num_same)
145: {
146: int changed;
147:
148: if (!bitmap || nb_sectors == 0) {
149: *num_same = nb_sectors;
150: return 0;
151: }
152:
153: changed = is_bit_set(bitmap, sector_num);
154: for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {
155: if (is_bit_set(bitmap, sector_num + *num_same) != changed)
156: break;
157: }
158:
159: return changed;
160: }
161:
162: static int cow_is_allocated(BlockDriverState *bs, int64_t sector_num,
163: int nb_sectors, int *pnum)
164: {
165: BDRVCowState *s = bs->opaque;
166: return is_changed(s->cow_bitmap, sector_num, nb_sectors, pnum);
167: }
168:
169: static int cow_read(BlockDriverState *bs, int64_t sector_num,
170: uint8_t *buf, int nb_sectors)
171: {
172: BDRVCowState *s = bs->opaque;
173: int ret, n;
174:
175: while (nb_sectors > 0) {
176: if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) {
177: lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
178: ret = read(s->fd, buf, n * 512);
179: if (ret != n * 512)
180: return -1;
181: } else {
182: memset(buf, 0, n * 512);
183: }
184: nb_sectors -= n;
185: sector_num += n;
186: buf += n * 512;
187: }
188: return 0;
189: }
190:
191: static int cow_write(BlockDriverState *bs, int64_t sector_num,
192: const uint8_t *buf, int nb_sectors)
193: {
194: BDRVCowState *s = bs->opaque;
195: int ret, i;
196:
197: lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
198: ret = write(s->fd, buf, nb_sectors * 512);
199: if (ret != nb_sectors * 512)
200: return -1;
201: for (i = 0; i < nb_sectors; i++)
202: cow_set_bit(s->cow_bitmap, sector_num + i);
203: return 0;
204: }
205:
206: static void cow_close(BlockDriverState *bs)
207: {
208: BDRVCowState *s = bs->opaque;
209: munmap(s->cow_bitmap_addr, s->cow_bitmap_size);
210: close(s->fd);
211: }
212:
213: static int cow_create(const char *filename, int64_t image_sectors,
214: const char *image_filename, int flags)
215: {
216: int fd, cow_fd;
217: struct cow_header_v2 cow_header;
218: struct stat st;
219:
220: if (flags)
221: return -ENOTSUP;
222:
223: cow_fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE,
224: 0644);
225: if (cow_fd < 0)
226: return -1;
227: memset(&cow_header, 0, sizeof(cow_header));
228: cow_header.magic = cpu_to_be32(COW_MAGIC);
229: cow_header.version = cpu_to_be32(COW_VERSION);
230: if (image_filename) {
231: fd = open(image_filename, O_RDONLY | O_BINARY);
232: if (fd < 0) {
233: close(cow_fd);
234: return -1;
235: }
236: if (fstat(fd, &st) != 0) {
237: close(fd);
238: return -1;
239: }
240: close(fd);
241: cow_header.mtime = cpu_to_be32(st.st_mtime);
242: realpath(image_filename, cow_header.backing_file);
243: }
244: cow_header.sectorsize = cpu_to_be32(512);
245: cow_header.size = cpu_to_be64(image_sectors * 512);
246: write(cow_fd, &cow_header, sizeof(cow_header));
247: /* resize to include at least all the bitmap */
248: ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3));
249: close(cow_fd);
250: return 0;
251: }
252:
1.1.1.2 ! root 253: static void cow_flush(BlockDriverState *bs)
! 254: {
! 255: BDRVCowState *s = bs->opaque;
! 256: fsync(s->fd);
! 257: }
! 258:
1.1 root 259: BlockDriver bdrv_cow = {
260: "cow",
261: sizeof(BDRVCowState),
262: cow_probe,
263: cow_open,
264: cow_read,
265: cow_write,
266: cow_close,
267: cow_create,
1.1.1.2 ! root 268: cow_flush,
1.1 root 269: cow_is_allocated,
270: };
271: #endif
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