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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.
*/
#include "qemu-common.h"
#include "block/block_int.h"
#include "qemu/module.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 {
CoMutex lock;
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, QDict *options, int flags)
{
BDRVCowState *s = bs->opaque;
struct cow_header_v2 cow_header;
int bitmap_size;
int64_t size;
int ret;
/* see if it is a cow image */
ret = bdrv_pread(bs->file, 0, &cow_header, sizeof(cow_header));
if (ret < 0) {
goto fail;
}
if (be32_to_cpu(cow_header.magic) != COW_MAGIC) {
ret = -EMEDIUMTYPE;
goto fail;
}
if (be32_to_cpu(cow_header.version) != COW_VERSION) {
char version[64];
snprintf(version, sizeof(version),
"COW version %d", cow_header.version);
qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
bs->device_name, "cow", version);
ret = -ENOTSUP;
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);
bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
s->cow_sectors_offset = (bitmap_size + 511) & ~511;
qemu_co_mutex_init(&s->lock);
return 0;
fail:
return ret;
}
/*
* XXX(hch): right now these functions are extremely inefficient.
* We should just read the whole bitmap we'll need in one go instead.
*/
static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum, bool *first)
{
uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
uint8_t bitmap;
int ret;
ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
if (ret < 0) {
return ret;
}
if (bitmap & (1 << (bitnum % 8))) {
return 0;
}
if (*first) {
ret = bdrv_flush(bs->file);
if (ret < 0) {
return ret;
}
*first = false;
}
bitmap |= (1 << (bitnum % 8));
ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap));
if (ret < 0) {
return ret;
}
return 0;
}
#define BITS_PER_BITMAP_SECTOR (512 * 8)
/* Cannot use bitmap.c on big-endian machines. */
static int cow_test_bit(int64_t bitnum, const uint8_t *bitmap)
{
return (bitmap[bitnum / 8] & (1 << (bitnum & 7))) != 0;
}
static int cow_find_streak(const uint8_t *bitmap, int value, int start, int nb_sectors)
{
int streak_value = value ? 0xFF : 0;
int last = MIN(start + nb_sectors, BITS_PER_BITMAP_SECTOR);
int bitnum = start;
while (bitnum < last) {
if ((bitnum & 7) == 0 && bitmap[bitnum / 8] == streak_value) {
bitnum += 8;
continue;
}
if (cow_test_bit(bitnum, bitmap) == value) {
bitnum++;
continue;
}
break;
}
return MIN(bitnum, last) - start;
}
/* 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 int coroutine_fn cow_co_is_allocated(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, int *num_same)
{
int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;
uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;
uint8_t bitmap[BDRV_SECTOR_SIZE];
int ret;
int changed;
ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
if (ret < 0) {
return ret;
}
bitnum &= BITS_PER_BITMAP_SECTOR - 1;
changed = cow_test_bit(bitnum, bitmap);
*num_same = cow_find_streak(bitmap, changed, bitnum, nb_sectors);
return changed;
}
static int64_t coroutine_fn cow_co_get_block_status(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, int *num_same)
{
BDRVCowState *s = bs->opaque;
int ret = cow_co_is_allocated(bs, sector_num, nb_sectors, num_same);
int64_t offset = s->cow_sectors_offset + (sector_num << BDRV_SECTOR_BITS);
if (ret < 0) {
return ret;
}
return (ret ? BDRV_BLOCK_DATA : 0) | offset | BDRV_BLOCK_OFFSET_VALID;
}
static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
int nb_sectors)
{
int error = 0;
int i;
bool first = true;
for (i = 0; i < nb_sectors; i++) {
error = cow_set_bit(bs, sector_num + i, &first);
if (error) {
break;
}
}
return error;
}
static int coroutine_fn 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) {
ret = cow_co_is_allocated(bs, sector_num, nb_sectors, &n);
if (ret < 0) {
return ret;
}
if (ret) {
ret = bdrv_pread(bs->file,
s->cow_sectors_offset + sector_num * 512,
buf, n * 512);
if (ret < 0) {
return ret;
}
} else {
if (bs->backing_hd) {
/* read from the base image */
ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
if (ret < 0) {
return ret;
}
} else {
memset(buf, 0, n * 512);
}
}
nb_sectors -= n;
sector_num += n;
buf += n * 512;
}
return 0;
}
static coroutine_fn int cow_co_read(BlockDriverState *bs, int64_t sector_num,
uint8_t *buf, int nb_sectors)
{
int ret;
BDRVCowState *s = bs->opaque;
qemu_co_mutex_lock(&s->lock);
ret = cow_read(bs, sector_num, buf, nb_sectors);
qemu_co_mutex_unlock(&s->lock);
return ret;
}
static int cow_write(BlockDriverState *bs, int64_t sector_num,
const uint8_t *buf, int nb_sectors)
{
BDRVCowState *s = bs->opaque;
int ret;
ret = bdrv_pwrite(bs->file, s->cow_sectors_offset + sector_num * 512,
buf, nb_sectors * 512);
if (ret < 0) {
return ret;
}
return cow_update_bitmap(bs, sector_num, nb_sectors);
}
static coroutine_fn int cow_co_write(BlockDriverState *bs, int64_t sector_num,
const uint8_t *buf, int nb_sectors)
{
int ret;
BDRVCowState *s = bs->opaque;
qemu_co_mutex_lock(&s->lock);
ret = cow_write(bs, sector_num, buf, nb_sectors);
qemu_co_mutex_unlock(&s->lock);
return ret;
}
static void cow_close(BlockDriverState *bs)
{
}
static int cow_create(const char *filename, QEMUOptionParameter *options)
{
struct cow_header_v2 cow_header;
struct stat st;
int64_t image_sectors = 0;
const char *image_filename = NULL;
int ret;
BlockDriverState *cow_bs;
/* 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++;
}
ret = bdrv_create_file(filename, options);
if (ret < 0) {
return ret;
}
ret = bdrv_file_open(&cow_bs, filename, NULL, BDRV_O_RDWR);
if (ret < 0) {
return ret;
}
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);
if (stat(image_filename, &st) != 0) {
goto mtime_fail;
}
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 = bdrv_pwrite(cow_bs, 0, &cow_header, sizeof(cow_header));
if (ret < 0) {
goto exit;
}
/* resize to include at least all the bitmap */
ret = bdrv_truncate(cow_bs,
sizeof(cow_header) + ((image_sectors + 7) >> 3));
if (ret < 0) {
goto exit;
}
exit:
bdrv_unref(cow_bs);
return ret;
}
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_open = cow_open,
.bdrv_close = cow_close,
.bdrv_create = cow_create,
.bdrv_has_zero_init = bdrv_has_zero_init_1,
.bdrv_read = cow_co_read,
.bdrv_write = cow_co_write,
.bdrv_co_get_block_status = cow_co_get_block_status,
.create_options = cow_create_options,
};
static void bdrv_cow_init(void)
{
bdrv_register(&bdrv_cow);
}
block_init(bdrv_cow_init);
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