Annotation of qemu/block-cow.c, revision 1.1

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: 
        !           253: BlockDriver bdrv_cow = {
        !           254:     "cow",
        !           255:     sizeof(BDRVCowState),
        !           256:     cow_probe,
        !           257:     cow_open,
        !           258:     cow_read,
        !           259:     cow_write,
        !           260:     cow_close,
        !           261:     cow_create,
        !           262:     cow_is_allocated,
        !           263: };
        !           264: #endif

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