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block: Enable BDRV_O_SNAPSHOT with driver-specific options 

In the case of snapshot=on, don't rely on the backing file path in the
temporary image any more, but override the backing file with the given
set of options. This way, block drivers that don't use a file name can
be accessed with snapshot=on, for example:

    -drive file.driver=nbd,file.host=localhost,snapshot=on

Which becomes internally something like:

    file.filename=/tmp/vl.AWQZCu,backing.file.driver=nbd,backing.file.host=localhost

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2013-11-14 15:37:12 +01:00
parent b59b3d5773
commit 9fd3171af9
1 changed files with 21 additions and 26 deletions
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47
block.c
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@ -1053,21 +1053,15 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
int64_t total_size;
BlockDriver *bdrv_qcow2;
QEMUOptionParameter *create_options;
char backing_filename[PATH_MAX];
if (qdict_size(options) != 0) {
error_setg(errp, "Can't use snapshot=on with driver-specific options");
ret = -EINVAL;
goto fail;
}
assert(filename != NULL);
QDict *snapshot_options;
/* if snapshot, we create a temporary backing file and open it
instead of opening 'filename' directly */
/* if there is a backing file, use it */
/* Get the required size from the image */
bs1 = bdrv_new("");
ret = bdrv_open(bs1, filename, NULL, 0, drv, &local_err);
QINCREF(options);
ret = bdrv_open(bs1, filename, options, 0, drv, &local_err);
if (ret < 0) {
bdrv_unref(bs1);
goto fail;
@ -1076,33 +1070,18 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
bdrv_unref(bs1);
/* Create the temporary image */
ret = get_tmp_filename(tmp_filename, sizeof(tmp_filename));
if (ret < 0) {
error_setg_errno(errp, -ret, "Could not get temporary filename");
goto fail;
}
/* Real path is meaningless for protocols */
if (path_has_protocol(filename)) {
snprintf(backing_filename, sizeof(backing_filename),
"%s", filename);
} else if (!realpath(filename, backing_filename)) {
ret = -errno;
error_setg_errno(errp, errno, "Could not resolve path '%s'", filename);
goto fail;
}
bdrv_qcow2 = bdrv_find_format("qcow2");
create_options = parse_option_parameters("", bdrv_qcow2->create_options,
NULL);
set_option_parameter_int(create_options, BLOCK_OPT_SIZE, total_size);
set_option_parameter(create_options, BLOCK_OPT_BACKING_FILE,
backing_filename);
if (drv) {
set_option_parameter(create_options, BLOCK_OPT_BACKING_FMT,
drv->format_name);
}
ret = bdrv_create(bdrv_qcow2, tmp_filename, create_options, &local_err);
free_option_parameters(create_options);
@ -1115,6 +1094,22 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
goto fail;
}
/* Prepare a new options QDict for the temporary file, where user
* options refer to the backing file */
if (filename) {
qdict_put(options, "file.filename", qstring_from_str(filename));
}
if (drv) {
qdict_put(options, "driver", qstring_from_str(drv->format_name));
}
snapshot_options = qdict_new();
qdict_put(snapshot_options, "backing", options);
qdict_flatten(snapshot_options);
bs->options = snapshot_options;
options = qdict_clone_shallow(bs->options);
filename = tmp_filename;
drv = bdrv_qcow2;
bs->is_temporary = 1;