root / block-cow.c @ f97572e5
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/*
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* Block driver for the COW format
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*
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* Copyright (c) 2004 Fabrice Bellard
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#ifndef _WIN32
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#include "qemu-common.h" |
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#include "block_int.h" |
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#include <sys/mman.h> |
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/**************************************************************/
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/* COW block driver using file system holes */
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/* user mode linux compatible COW file */
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#define COW_MAGIC 0x4f4f4f4d /* MOOO */ |
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#define COW_VERSION 2 |
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struct cow_header_v2 {
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uint32_t magic; |
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uint32_t version; |
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char backing_file[1024]; |
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int32_t mtime; |
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uint64_t size; |
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uint32_t sectorsize; |
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}; |
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typedef struct BDRVCowState { |
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int fd;
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uint8_t *cow_bitmap; /* if non NULL, COW mappings are used first */
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uint8_t *cow_bitmap_addr; /* mmap address of cow_bitmap */
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int cow_bitmap_size;
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int64_t cow_sectors_offset; |
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} BDRVCowState; |
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static int cow_probe(const uint8_t *buf, int buf_size, const char *filename) |
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{ |
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const struct cow_header_v2 *cow_header = (const void *)buf; |
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if (buf_size >= sizeof(struct cow_header_v2) && |
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be32_to_cpu(cow_header->magic) == COW_MAGIC && |
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be32_to_cpu(cow_header->version) == COW_VERSION) |
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return 100; |
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else
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return 0; |
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} |
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static int cow_open(BlockDriverState *bs, const char *filename, int flags) |
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{ |
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BDRVCowState *s = bs->opaque; |
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int fd;
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struct cow_header_v2 cow_header;
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int64_t size; |
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fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE); |
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if (fd < 0) { |
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fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE); |
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if (fd < 0) |
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return -1; |
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} |
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s->fd = fd; |
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/* see if it is a cow image */
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if (read(fd, &cow_header, sizeof(cow_header)) != sizeof(cow_header)) { |
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goto fail;
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} |
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if (be32_to_cpu(cow_header.magic) != COW_MAGIC ||
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be32_to_cpu(cow_header.version) != COW_VERSION) { |
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goto fail;
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} |
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/* cow image found */
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size = be64_to_cpu(cow_header.size); |
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bs->total_sectors = size / 512;
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pstrcpy(bs->backing_file, sizeof(bs->backing_file),
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cow_header.backing_file); |
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/* mmap the bitmap */
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s->cow_bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header); |
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s->cow_bitmap_addr = mmap(get_mmap_addr(s->cow_bitmap_size), |
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s->cow_bitmap_size, |
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PROT_READ | PROT_WRITE, |
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MAP_SHARED, s->fd, 0);
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if (s->cow_bitmap_addr == MAP_FAILED)
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goto fail;
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s->cow_bitmap = s->cow_bitmap_addr + sizeof(cow_header);
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s->cow_sectors_offset = (s->cow_bitmap_size + 511) & ~511; |
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return 0; |
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fail:
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close(fd); |
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return -1; |
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} |
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static inline void cow_set_bit(uint8_t *bitmap, int64_t bitnum) |
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{ |
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bitmap[bitnum / 8] |= (1 << (bitnum%8)); |
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} |
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static inline int is_bit_set(const uint8_t *bitmap, int64_t bitnum) |
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{ |
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return !!(bitmap[bitnum / 8] & (1 << (bitnum%8))); |
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} |
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/* Return true if first block has been changed (ie. current version is
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* in COW file). Set the number of continuous blocks for which that
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* is true. */
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static inline int is_changed(uint8_t *bitmap, |
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int64_t sector_num, int nb_sectors,
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int *num_same)
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{ |
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int changed;
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if (!bitmap || nb_sectors == 0) { |
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*num_same = nb_sectors; |
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return 0; |
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} |
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changed = is_bit_set(bitmap, sector_num); |
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for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) { |
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if (is_bit_set(bitmap, sector_num + *num_same) != changed)
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break;
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} |
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return changed;
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} |
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static int cow_is_allocated(BlockDriverState *bs, int64_t sector_num, |
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int nb_sectors, int *pnum) |
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{ |
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BDRVCowState *s = bs->opaque; |
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return is_changed(s->cow_bitmap, sector_num, nb_sectors, pnum);
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} |
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static int cow_read(BlockDriverState *bs, int64_t sector_num, |
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uint8_t *buf, int nb_sectors)
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{ |
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BDRVCowState *s = bs->opaque; |
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int ret, n;
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while (nb_sectors > 0) { |
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if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) {
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lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
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ret = read(s->fd, buf, n * 512);
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if (ret != n * 512) |
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return -1; |
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} else {
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if (bs->backing_hd) {
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/* read from the base image */
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ret = bdrv_read(bs->backing_hd, sector_num, buf, n); |
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if (ret < 0) |
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return -1; |
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} else {
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memset(buf, 0, n * 512); |
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} |
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} |
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nb_sectors -= n; |
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sector_num += n; |
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buf += n * 512;
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} |
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return 0; |
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} |
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static int cow_write(BlockDriverState *bs, int64_t sector_num, |
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const uint8_t *buf, int nb_sectors) |
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{ |
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BDRVCowState *s = bs->opaque; |
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int ret, i;
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lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
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ret = write(s->fd, buf, nb_sectors * 512);
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if (ret != nb_sectors * 512) |
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return -1; |
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for (i = 0; i < nb_sectors; i++) |
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cow_set_bit(s->cow_bitmap, sector_num + i); |
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return 0; |
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} |
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static void cow_close(BlockDriverState *bs) |
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{ |
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BDRVCowState *s = bs->opaque; |
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munmap(s->cow_bitmap_addr, s->cow_bitmap_size); |
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close(s->fd); |
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} |
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static int cow_create(const char *filename, int64_t image_sectors, |
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const char *image_filename, int flags) |
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{ |
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int fd, cow_fd;
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struct cow_header_v2 cow_header;
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struct stat st;
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if (flags)
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return -ENOTSUP;
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cow_fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, |
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0644);
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if (cow_fd < 0) |
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return -1; |
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memset(&cow_header, 0, sizeof(cow_header)); |
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cow_header.magic = cpu_to_be32(COW_MAGIC); |
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cow_header.version = cpu_to_be32(COW_VERSION); |
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if (image_filename) {
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/* Note: if no file, we put a dummy mtime */
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cow_header.mtime = cpu_to_be32(0);
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fd = open(image_filename, O_RDONLY | O_BINARY); |
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if (fd < 0) { |
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close(cow_fd); |
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goto mtime_fail;
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} |
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if (fstat(fd, &st) != 0) { |
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close(fd); |
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goto mtime_fail;
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} |
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close(fd); |
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cow_header.mtime = cpu_to_be32(st.st_mtime); |
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mtime_fail:
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pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
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image_filename); |
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} |
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cow_header.sectorsize = cpu_to_be32(512);
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cow_header.size = cpu_to_be64(image_sectors * 512);
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write(cow_fd, &cow_header, sizeof(cow_header));
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/* resize to include at least all the bitmap */
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ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3)); |
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close(cow_fd); |
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return 0; |
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} |
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static void cow_flush(BlockDriverState *bs) |
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{ |
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BDRVCowState *s = bs->opaque; |
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fsync(s->fd); |
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} |
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BlockDriver bdrv_cow = { |
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"cow",
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sizeof(BDRVCowState),
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cow_probe, |
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cow_open, |
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cow_read, |
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cow_write, |
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cow_close, |
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cow_create, |
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cow_flush, |
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cow_is_allocated, |
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}; |
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#endif
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