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qemu/block/cow.c

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/*
* 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
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