There are two different types of flush that you can do: Flushing one level up to the OS (i.e. writing data to the host page cache) or flushing it all the way down to the disk. The existing functions flush to the disk, reflect this in the function name. Signed-off-by: Kevin Wolf <kwolf@redhat.com>
351 lines
9.4 KiB
C
351 lines
9.4 KiB
C
/*
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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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#include "qemu-common.h"
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#include "block_int.h"
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#include "module.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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CoMutex lock;
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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, int flags)
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{
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BDRVCowState *s = bs->opaque;
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struct cow_header_v2 cow_header;
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int bitmap_size;
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int64_t size;
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/* see if it is a cow image */
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if (bdrv_pread(bs->file, 0, &cow_header, sizeof(cow_header)) !=
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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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bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
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s->cow_sectors_offset = (bitmap_size + 511) & ~511;
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qemu_co_mutex_init(&s->lock);
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return 0;
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fail:
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return -1;
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}
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/*
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* XXX(hch): right now these functions are extremly ineffcient.
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* We should just read the whole bitmap we'll need in one go instead.
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*/
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static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum)
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{
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uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
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uint8_t bitmap;
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int ret;
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ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
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if (ret < 0) {
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return ret;
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}
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bitmap |= (1 << (bitnum % 8));
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ret = bdrv_pwrite_sync(bs->file, offset, &bitmap, sizeof(bitmap));
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if (ret < 0) {
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return ret;
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}
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return 0;
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}
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static inline int is_bit_set(BlockDriverState *bs, int64_t bitnum)
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{
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uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
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uint8_t bitmap;
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int ret;
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ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
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if (ret < 0) {
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return ret;
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}
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return !!(bitmap & (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 int cow_is_allocated(BlockDriverState *bs, int64_t sector_num,
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int nb_sectors, int *num_same)
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{
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int changed;
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if (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(bs, sector_num);
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if (changed < 0) {
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return 0; /* XXX: how to return I/O errors? */
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}
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for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {
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if (is_bit_set(bs, 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_update_bitmap(BlockDriverState *bs, int64_t sector_num,
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int nb_sectors)
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{
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int error = 0;
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int i;
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for (i = 0; i < nb_sectors; i++) {
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error = cow_set_bit(bs, sector_num + i);
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if (error) {
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break;
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}
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}
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return error;
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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 (cow_is_allocated(bs, sector_num, nb_sectors, &n)) {
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ret = bdrv_pread(bs->file,
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s->cow_sectors_offset + sector_num * 512,
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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 coroutine_fn int cow_co_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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int ret;
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BDRVCowState *s = bs->opaque;
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qemu_co_mutex_lock(&s->lock);
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ret = cow_read(bs, sector_num, buf, nb_sectors);
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qemu_co_mutex_unlock(&s->lock);
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return ret;
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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;
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ret = bdrv_pwrite(bs->file, s->cow_sectors_offset + sector_num * 512,
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buf, nb_sectors * 512);
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if (ret != nb_sectors * 512)
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return -1;
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return cow_update_bitmap(bs, sector_num, nb_sectors);
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}
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static coroutine_fn int cow_co_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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int ret;
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BDRVCowState *s = bs->opaque;
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qemu_co_mutex_lock(&s->lock);
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ret = cow_write(bs, sector_num, buf, nb_sectors);
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qemu_co_mutex_unlock(&s->lock);
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return ret;
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}
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static void cow_close(BlockDriverState *bs)
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{
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}
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static int cow_create(const char *filename, QEMUOptionParameter *options)
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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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int64_t image_sectors = 0;
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const char *image_filename = NULL;
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int ret;
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/* Read out options */
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while (options && options->name) {
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if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
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image_sectors = options->value.n / 512;
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} else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
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image_filename = options->value.s;
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}
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options++;
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}
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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 -errno;
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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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ret = qemu_write_full(cow_fd, &cow_header, sizeof(cow_header));
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if (ret != sizeof(cow_header)) {
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ret = -errno;
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goto exit;
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}
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/* resize to include at least all the bitmap */
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ret = ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3));
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if (ret) {
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ret = -errno;
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goto exit;
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}
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exit:
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close(cow_fd);
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return ret;
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}
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static coroutine_fn int cow_co_flush(BlockDriverState *bs)
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{
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return bdrv_co_flush(bs->file);
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}
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static QEMUOptionParameter cow_create_options[] = {
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{
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.name = BLOCK_OPT_SIZE,
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.type = OPT_SIZE,
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.help = "Virtual disk size"
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},
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{
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.name = BLOCK_OPT_BACKING_FILE,
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.type = OPT_STRING,
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.help = "File name of a base image"
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},
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{ NULL }
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};
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static BlockDriver bdrv_cow = {
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.format_name = "cow",
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.instance_size = sizeof(BDRVCowState),
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.bdrv_probe = cow_probe,
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.bdrv_open = cow_open,
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.bdrv_close = cow_close,
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.bdrv_create = cow_create,
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.bdrv_read = cow_co_read,
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.bdrv_write = cow_co_write,
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.bdrv_co_flush_to_disk = cow_co_flush,
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.bdrv_is_allocated = cow_is_allocated,
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.create_options = cow_create_options,
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};
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static void bdrv_cow_init(void)
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{
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bdrv_register(&bdrv_cow);
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}
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block_init(bdrv_cow_init);
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