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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