/* * Block driver for the COW format * * Copyright (c) 2004 Fabrice Bellard * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */ #ifndef _WIN32 #include "qemu-common.h" #include "block_int.h" #include "module.h" #include <sys/mman.h> /**************************************************************/ /* COW block driver using file system holes */ /* user mode linux compatible COW file */ #define COW_MAGIC 0x4f4f4f4d /* MOOO */ #define COW_VERSION 2 struct cow_header_v2 { uint32_t magic; uint32_t version; char backing_file[1024]; int32_t mtime; uint64_t size; uint32_t sectorsize; }; typedef struct BDRVCowState { int fd; uint8_t *cow_bitmap; /* if non NULL, COW mappings are used first */ uint8_t *cow_bitmap_addr; /* mmap address of cow_bitmap */ int cow_bitmap_size; int64_t cow_sectors_offset; } BDRVCowState; static int cow_probe(const uint8_t *buf, int buf_size, const char *filename) { const struct cow_header_v2 *cow_header = (const void *)buf; if (buf_size >= sizeof(struct cow_header_v2) && be32_to_cpu(cow_header->magic) == COW_MAGIC && be32_to_cpu(cow_header->version) == COW_VERSION) return 100; else return 0; } static int cow_open(BlockDriverState *bs, const char *filename, int flags) { BDRVCowState *s = bs->opaque; int fd; struct cow_header_v2 cow_header; int64_t size; fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE); if (fd < 0) { fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE); if (fd < 0) return -1; } s->fd = fd; /* see if it is a cow image */ if (read(fd, &cow_header, sizeof(cow_header)) != sizeof(cow_header)) { goto fail; } if (be32_to_cpu(cow_header.magic) != COW_MAGIC || be32_to_cpu(cow_header.version) != COW_VERSION) { goto fail; } /* cow image found */ size = be64_to_cpu(cow_header.size); bs->total_sectors = size / 512; pstrcpy(bs->backing_file, sizeof(bs->backing_file), cow_header.backing_file); /* mmap the bitmap */ s->cow_bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header); s->cow_bitmap_addr = (void *)mmap(get_mmap_addr(s->cow_bitmap_size), s->cow_bitmap_size, PROT_READ | PROT_WRITE, MAP_SHARED, s->fd, 0); if (s->cow_bitmap_addr == MAP_FAILED) goto fail; s->cow_bitmap = s->cow_bitmap_addr + sizeof(cow_header); s->cow_sectors_offset = (s->cow_bitmap_size + 511) & ~511; return 0; fail: close(fd); return -1; } static inline void cow_set_bit(uint8_t *bitmap, int64_t bitnum) { bitmap[bitnum / 8] |= (1 << (bitnum%8)); } static inline int is_bit_set(const uint8_t *bitmap, int64_t bitnum) { return !!(bitmap[bitnum / 8] & (1 << (bitnum%8))); } /* Return true if first block has been changed (ie. current version is * in COW file). Set the number of continuous blocks for which that * is true. */ static inline int is_changed(uint8_t *bitmap, int64_t sector_num, int nb_sectors, int *num_same) { int changed; if (!bitmap || nb_sectors == 0) { *num_same = nb_sectors; return 0; } changed = is_bit_set(bitmap, sector_num); for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) { if (is_bit_set(bitmap, sector_num + *num_same) != changed) break; } return changed; } static int cow_is_allocated(BlockDriverState *bs, int64_t sector_num, int nb_sectors, int *pnum) { BDRVCowState *s = bs->opaque; return is_changed(s->cow_bitmap, sector_num, nb_sectors, pnum); } static int cow_read(BlockDriverState *bs, int64_t sector_num, uint8_t *buf, int nb_sectors) { BDRVCowState *s = bs->opaque; int ret, n; while (nb_sectors > 0) { if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) { lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET); ret = read(s->fd, buf, n * 512); if (ret != n * 512) return -1; } else { if (bs->backing_hd) { /* read from the base image */ ret = bdrv_read(bs->backing_hd, sector_num, buf, n); if (ret < 0) return -1; } else { memset(buf, 0, n * 512); } } nb_sectors -= n; sector_num += n; buf += n * 512; } return 0; } static int cow_write(BlockDriverState *bs, int64_t sector_num, const uint8_t *buf, int nb_sectors) { BDRVCowState *s = bs->opaque; int ret, i; lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET); ret = write(s->fd, buf, nb_sectors * 512); if (ret != nb_sectors * 512) return -1; for (i = 0; i < nb_sectors; i++) cow_set_bit(s->cow_bitmap, sector_num + i); return 0; } static void cow_close(BlockDriverState *bs) { BDRVCowState *s = bs->opaque; munmap((void *)s->cow_bitmap_addr, s->cow_bitmap_size); close(s->fd); } static int cow_create(const char *filename, QEMUOptionParameter *options) { int fd, cow_fd; struct cow_header_v2 cow_header; struct stat st; int64_t image_sectors = 0; const char *image_filename = NULL; int ret; /* Read out options */ while (options && options->name) { if (!strcmp(options->name, BLOCK_OPT_SIZE)) { image_sectors = options->value.n / 512; } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) { image_filename = options->value.s; } options++; } cow_fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, 0644); if (cow_fd < 0) return -errno; memset(&cow_header, 0, sizeof(cow_header)); cow_header.magic = cpu_to_be32(COW_MAGIC); cow_header.version = cpu_to_be32(COW_VERSION); if (image_filename) { /* Note: if no file, we put a dummy mtime */ cow_header.mtime = cpu_to_be32(0); fd = open(image_filename, O_RDONLY | O_BINARY); if (fd < 0) { close(cow_fd); goto mtime_fail; } if (fstat(fd, &st) != 0) { close(fd); goto mtime_fail; } close(fd); cow_header.mtime = cpu_to_be32(st.st_mtime); mtime_fail: pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file), image_filename); } cow_header.sectorsize = cpu_to_be32(512); cow_header.size = cpu_to_be64(image_sectors * 512); ret = qemu_write_full(cow_fd, &cow_header, sizeof(cow_header)); if (ret != sizeof(cow_header)) { ret = -errno; goto exit; } /* resize to include at least all the bitmap */ ret = ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3)); if (ret) { ret = -errno; goto exit; } exit: close(cow_fd); return ret; } static void cow_flush(BlockDriverState *bs) { BDRVCowState *s = bs->opaque; qemu_fdatasync(s->fd); } static QEMUOptionParameter cow_create_options[] = { { .name = BLOCK_OPT_SIZE, .type = OPT_SIZE, .help = "Virtual disk size" }, { .name = BLOCK_OPT_BACKING_FILE, .type = OPT_STRING, .help = "File name of a base image" }, { NULL } }; static BlockDriver bdrv_cow = { .format_name = "cow", .instance_size = sizeof(BDRVCowState), .bdrv_probe = cow_probe, .bdrv_file_open = cow_open, .bdrv_read = cow_read, .bdrv_write = cow_write, .bdrv_close = cow_close, .bdrv_create = cow_create, .bdrv_flush = cow_flush, .bdrv_is_allocated = cow_is_allocated, .create_options = cow_create_options, }; static void bdrv_cow_init(void) { bdrv_register(&bdrv_cow); } block_init(bdrv_cow_init); #endif