qemu/block/cow.c
Kevin Wolf 66f82ceed6 block: Open the underlying image file in generic code
Format drivers shouldn't need to bother with things like file names, but rather
just get an open BlockDriverState for the underlying protocol. This patch
introduces this behaviour for bdrv_open implementation. For protocols which
need to access the filename to open their file/device/connection/... a new
callback bdrv_file_open is introduced which doesn't get an underlying file
opened.

For now, also some of the more obscure formats use bdrv_file_open because they
open() the file themselves instead of using the block.c functions. They need to
be fixed in later patches.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2010-05-03 10:07:30 +02:00

312 lines
8.9 KiB
C

/*
* 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