BlockBackend *blk = NULL, *blk_old_backing = NULL, *blk_new_backing = NULL;
uint8_t *buf_old = NULL;
uint8_t *buf_new = NULL;
- BlockDriverState *bs = NULL;
+ BlockDriverState *bs = NULL, *prefix_chain_bs = NULL;
char *filename;
const char *fmt, *cache, *src_cache, *out_basefmt, *out_baseimg;
int c, flags, src_flags, ret;
/* For safe rebasing we need to compare old and new backing file */
if (!unsafe) {
- char backing_name[PATH_MAX];
QDict *options = NULL;
-
- if (bs->backing_format[0] != '\0') {
- options = qdict_new();
- qdict_put_str(options, "driver", bs->backing_format);
- }
-
- if (force_share) {
- if (!options) {
- options = qdict_new();
+ BlockDriverState *base_bs = backing_bs(bs);
+
+ if (base_bs) {
+ blk_old_backing = blk_new(qemu_get_aio_context(),
+ BLK_PERM_CONSISTENT_READ,
+ BLK_PERM_ALL);
+ ret = blk_insert_bs(blk_old_backing, base_bs,
+ &local_err);
+ if (ret < 0) {
+ error_reportf_err(local_err,
+ "Could not reuse old backing file '%s': ",
+ base_bs->filename);
+ goto out;
}
- qdict_put_bool(options, BDRV_OPT_FORCE_SHARE, true);
- }
- bdrv_get_backing_filename(bs, backing_name, sizeof(backing_name));
- blk_old_backing = blk_new_open(backing_name, NULL,
- options, src_flags, &local_err);
- if (!blk_old_backing) {
- error_reportf_err(local_err,
- "Could not open old backing file '%s': ",
- backing_name);
- ret = -1;
- goto out;
+ } else {
+ blk_old_backing = NULL;
}
if (out_baseimg[0]) {
goto out;
}
- blk_new_backing = blk_new_open(out_real_path, NULL,
- options, src_flags, &local_err);
- g_free(out_real_path);
- if (!blk_new_backing) {
- error_reportf_err(local_err,
- "Could not open new backing file '%s': ",
- out_baseimg);
- ret = -1;
- goto out;
+ /*
+ * Find out whether we rebase an image on top of a previous image
+ * in its chain.
+ */
+ prefix_chain_bs = bdrv_find_backing_image(bs, out_real_path);
+ if (prefix_chain_bs) {
+ g_free(out_real_path);
+ blk_new_backing = blk_new(qemu_get_aio_context(),
+ BLK_PERM_CONSISTENT_READ,
+ BLK_PERM_ALL);
+ ret = blk_insert_bs(blk_new_backing, prefix_chain_bs,
+ &local_err);
+ if (ret < 0) {
+ error_reportf_err(local_err,
+ "Could not reuse backing file '%s': ",
+ out_baseimg);
+ goto out;
+ }
+ } else {
+ blk_new_backing = blk_new_open(out_real_path, NULL,
+ options, src_flags, &local_err);
+ g_free(out_real_path);
+ if (!blk_new_backing) {
+ error_reportf_err(local_err,
+ "Could not open new backing file '%s': ",
+ out_baseimg);
+ ret = -1;
+ goto out;
+ }
}
}
}
*/
if (!unsafe) {
int64_t size;
- int64_t old_backing_size;
+ int64_t old_backing_size = 0;
int64_t new_backing_size = 0;
uint64_t offset;
int64_t n;
ret = -1;
goto out;
}
- old_backing_size = blk_getlength(blk_old_backing);
- if (old_backing_size < 0) {
- char backing_name[PATH_MAX];
+ if (blk_old_backing) {
+ old_backing_size = blk_getlength(blk_old_backing);
+ if (old_backing_size < 0) {
+ char backing_name[PATH_MAX];
- bdrv_get_backing_filename(bs, backing_name, sizeof(backing_name));
- error_report("Could not get size of '%s': %s",
- backing_name, strerror(-old_backing_size));
- ret = -1;
- goto out;
+ bdrv_get_backing_filename(bs, backing_name,
+ sizeof(backing_name));
+ error_report("Could not get size of '%s': %s",
+ backing_name, strerror(-old_backing_size));
+ ret = -1;
+ goto out;
+ }
}
if (blk_new_backing) {
new_backing_size = blk_getlength(blk_new_backing);
}
for (offset = 0; offset < size; offset += n) {
+ bool buf_old_is_zero = false;
+
/* How many bytes can we handle with the next read? */
n = MIN(IO_BUF_SIZE, size - offset);
continue;
}
+ if (prefix_chain_bs) {
+ /*
+ * If cluster wasn't changed since prefix_chain, we don't need
+ * to take action
+ */
+ ret = bdrv_is_allocated_above(backing_bs(bs), prefix_chain_bs,
+ offset, n, &n);
+ if (ret < 0) {
+ error_report("error while reading image metadata: %s",
+ strerror(-ret));
+ goto out;
+ }
+ if (!ret) {
+ continue;
+ }
+ }
+
/*
* Read old and new backing file and take into consideration that
* backing files may be smaller than the COW image.
*/
if (offset >= old_backing_size) {
memset(buf_old, 0, n);
+ buf_old_is_zero = true;
} else {
if (offset + n > old_backing_size) {
n = old_backing_size - offset;
if (compare_buffers(buf_old + written, buf_new + written,
n - written, &pnum))
{
- ret = blk_pwrite(blk, offset + written,
- buf_old + written, pnum, 0);
+ if (buf_old_is_zero) {
+ ret = blk_pwrite_zeroes(blk, offset + written, pnum, 0);
+ } else {
+ ret = blk_pwrite(blk, offset + written,
+ buf_old + written, pnum, 0);
+ }
if (ret < 0) {
error_report("Error while writing to COW image: %s",
strerror(-ret));