in qemu-img.c [3437:3855]
static int img_rebase(int argc, char **argv)
{
BlockBackend *blk = NULL, *blk_old_backing = NULL, *blk_new_backing = NULL;
uint8_t *buf_old = NULL;
uint8_t *buf_new = NULL;
BlockDriverState *bs = NULL, *prefix_chain_bs = NULL;
BlockDriverState *unfiltered_bs;
char *filename;
const char *fmt, *cache, *src_cache, *out_basefmt, *out_baseimg;
int c, flags, src_flags, ret;
bool writethrough, src_writethrough;
int unsafe = 0;
bool force_share = false;
int progress = 0;
bool quiet = false;
Error *local_err = NULL;
bool image_opts = false;
/* Parse commandline parameters */
fmt = NULL;
cache = BDRV_DEFAULT_CACHE;
src_cache = BDRV_DEFAULT_CACHE;
out_baseimg = NULL;
out_basefmt = NULL;
for(;;) {
static const struct option long_options[] = {
{"help", no_argument, 0, 'h'},
{"object", required_argument, 0, OPTION_OBJECT},
{"image-opts", no_argument, 0, OPTION_IMAGE_OPTS},
{"force-share", no_argument, 0, 'U'},
{0, 0, 0, 0}
};
c = getopt_long(argc, argv, ":hf:F:b:upt:T:qU",
long_options, NULL);
if (c == -1) {
break;
}
switch(c) {
case ':':
missing_argument(argv[optind - 1]);
break;
case '?':
unrecognized_option(argv[optind - 1]);
break;
case 'h':
help();
return 0;
case 'f':
fmt = optarg;
break;
case 'F':
out_basefmt = optarg;
break;
case 'b':
out_baseimg = optarg;
break;
case 'u':
unsafe = 1;
break;
case 'p':
progress = 1;
break;
case 't':
cache = optarg;
break;
case 'T':
src_cache = optarg;
break;
case 'q':
quiet = true;
break;
case OPTION_OBJECT:
user_creatable_process_cmdline(optarg);
break;
case OPTION_IMAGE_OPTS:
image_opts = true;
break;
case 'U':
force_share = true;
break;
}
}
if (quiet) {
progress = 0;
}
if (optind != argc - 1) {
error_exit("Expecting one image file name");
}
if (!unsafe && !out_baseimg) {
error_exit("Must specify backing file (-b) or use unsafe mode (-u)");
}
filename = argv[optind++];
qemu_progress_init(progress, 2.0);
qemu_progress_print(0, 100);
flags = BDRV_O_RDWR | (unsafe ? BDRV_O_NO_BACKING : 0);
ret = bdrv_parse_cache_mode(cache, &flags, &writethrough);
if (ret < 0) {
error_report("Invalid cache option: %s", cache);
goto out;
}
src_flags = 0;
ret = bdrv_parse_cache_mode(src_cache, &src_flags, &src_writethrough);
if (ret < 0) {
error_report("Invalid source cache option: %s", src_cache);
goto out;
}
/* The source files are opened read-only, don't care about WCE */
assert((src_flags & BDRV_O_RDWR) == 0);
(void) src_writethrough;
/*
* Open the images.
*
* Ignore the old backing file for unsafe rebase in case we want to correct
* the reference to a renamed or moved backing file.
*/
blk = img_open(image_opts, filename, fmt, flags, writethrough, quiet,
false);
if (!blk) {
ret = -1;
goto out;
}
bs = blk_bs(blk);
unfiltered_bs = bdrv_skip_filters(bs);
if (out_basefmt != NULL) {
if (bdrv_find_format(out_basefmt) == NULL) {
error_report("Invalid format name: '%s'", out_basefmt);
ret = -1;
goto out;
}
}
/* For safe rebasing we need to compare old and new backing file */
if (!unsafe) {
QDict *options = NULL;
BlockDriverState *base_bs = bdrv_cow_bs(unfiltered_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;
}
} else {
blk_old_backing = NULL;
}
if (out_baseimg[0]) {
const char *overlay_filename;
char *out_real_path;
options = qdict_new();
if (out_basefmt) {
qdict_put_str(options, "driver", out_basefmt);
}
if (force_share) {
qdict_put_bool(options, BDRV_OPT_FORCE_SHARE, true);
}
bdrv_refresh_filename(bs);
overlay_filename = bs->exact_filename[0] ? bs->exact_filename
: bs->filename;
out_real_path =
bdrv_get_full_backing_filename_from_filename(overlay_filename,
out_baseimg,
&local_err);
if (local_err) {
qobject_unref(options);
error_reportf_err(local_err,
"Could not resolve backing filename: ");
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) {
qobject_unref(options);
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;
}
}
}
}
/*
* Check each unallocated cluster in the COW file. If it is unallocated,
* accesses go to the backing file. We must therefore compare this cluster
* in the old and new backing file, and if they differ we need to copy it
* from the old backing file into the COW file.
*
* If qemu-img crashes during this step, no harm is done. The content of
* the image is the same as the original one at any time.
*/
if (!unsafe) {
int64_t size;
int64_t old_backing_size = 0;
int64_t new_backing_size = 0;
uint64_t offset;
int64_t n;
float local_progress = 0;
buf_old = blk_blockalign(blk, IO_BUF_SIZE);
buf_new = blk_blockalign(blk, IO_BUF_SIZE);
size = blk_getlength(blk);
if (size < 0) {
error_report("Could not get size of '%s': %s",
filename, strerror(-size));
ret = -1;
goto out;
}
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;
}
}
if (blk_new_backing) {
new_backing_size = blk_getlength(blk_new_backing);
if (new_backing_size < 0) {
error_report("Could not get size of '%s': %s",
out_baseimg, strerror(-new_backing_size));
ret = -1;
goto out;
}
}
if (size != 0) {
local_progress = (float)100 / (size / MIN(size, IO_BUF_SIZE));
}
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);
/* If the cluster is allocated, we don't need to take action */
ret = bdrv_is_allocated(unfiltered_bs, offset, n, &n);
if (ret < 0) {
error_report("error while reading image metadata: %s",
strerror(-ret));
goto out;
}
if (ret) {
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(bdrv_cow_bs(unfiltered_bs),
prefix_chain_bs, false,
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;
}
ret = blk_pread(blk_old_backing, offset, buf_old, n);
if (ret < 0) {
error_report("error while reading from old backing file");
goto out;
}
}
if (offset >= new_backing_size || !blk_new_backing) {
memset(buf_new, 0, n);
} else {
if (offset + n > new_backing_size) {
n = new_backing_size - offset;
}
ret = blk_pread(blk_new_backing, offset, buf_new, n);
if (ret < 0) {
error_report("error while reading from new backing file");
goto out;
}
}
/* If they differ, we need to write to the COW file */
uint64_t written = 0;
while (written < n) {
int64_t pnum;
if (compare_buffers(buf_old + written, buf_new + written,
n - written, &pnum))
{
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));
goto out;
}
}
written += pnum;
}
qemu_progress_print(local_progress, 100);
}
}
/*
* Change the backing file. All clusters that are different from the old
* backing file are overwritten in the COW file now, so the visible content
* doesn't change when we switch the backing file.
*/
if (out_baseimg && *out_baseimg) {
ret = bdrv_change_backing_file(unfiltered_bs, out_baseimg, out_basefmt,
true);
} else {
ret = bdrv_change_backing_file(unfiltered_bs, NULL, NULL, false);
}
if (ret == -ENOSPC) {
error_report("Could not change the backing file to '%s': No "
"space left in the file header", out_baseimg);
} else if (ret == -EINVAL && out_baseimg && !out_basefmt) {
error_report("Could not change the backing file to '%s': backing "
"format must be specified", out_baseimg);
} else if (ret < 0) {
error_report("Could not change the backing file to '%s': %s",
out_baseimg, strerror(-ret));
}
qemu_progress_print(100, 0);
/*
* TODO At this point it is possible to check if any clusters that are
* allocated in the COW file are the same in the backing file. If so, they
* could be dropped from the COW file. Don't do this before switching the
* backing file, in case of a crash this would lead to corruption.
*/
out:
qemu_progress_end();
/* Cleanup */
if (!unsafe) {
blk_unref(blk_old_backing);
blk_unref(blk_new_backing);
}
qemu_vfree(buf_old);
qemu_vfree(buf_new);
blk_unref(blk);
if (ret) {
return 1;
}
return 0;
}