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Re: [Qemu-devel] [PATCH v6 for 2.1 10/10] block: add QAPI command to all
From: |
Benoît Canet |
Subject: |
Re: [Qemu-devel] [PATCH v6 for 2.1 10/10] block: add QAPI command to allow live backing file change |
Date: |
Wed, 18 Jun 2014 15:15:07 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
The Tuesday 17 Jun 2014 à 17:53:58 (-0400), Jeff Cody wrote :
> This allows a user to make a live change to the backing file recorded in
> an open image.
>
> The image file to modify can be specified 2 ways:
>
> 1) image filename
> 2) image node-name
>
> Note: this does not cause the backing file itself to be reopened; it
> merely changes the backing filename in the image file structure, and
> in internal BDS structures.
>
> It is the responsibility of the user to pass a filename string that
> can be resolved when the image chain is reopened, and the filename
> string is not validated.
>
> A good analogy for this command is that it is a live version of
> 'qemu-img rebase -u', with respect to changing the backing file string.
>
> Reviewed-by: Eric Blake <address@hidden>
> Signed-off-by: Jeff Cody <address@hidden>
> ---
> blockdev.c | 102
> +++++++++++++++++++++++++++++++++++++++++++++++++++
> qapi/block-core.json | 60 ++++++++++++++++++++++++++++++
> qmp-commands.hx | 74 +++++++++++++++++++++++++++++++++++++
> 3 files changed, 236 insertions(+)
>
> diff --git a/blockdev.c b/blockdev.c
> index 42c7b3f..273e52a 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -2414,6 +2414,108 @@ void qmp_block_job_complete(const char *device, Error
> **errp)
> block_job_complete(job, errp);
> }
>
> +void qmp_change_backing_file(const char *device,
> + bool has_image, const char *image,
> + bool has_image_node_name,
> + const char *image_node_name,
> + const char *backing_file,
> + Error **errp)
> +{
> + BlockDriverState *bs = NULL;
> + BlockDriverState *image_bs = NULL;
> + Error *local_err = NULL;
> + bool ro;
> + int open_flags;
> + int ret;
> +
> + /* validate argument combinations */
> + if (has_image && has_image_node_name) {
> + error_setg(errp, "'image' and 'image-node-name' "
> + "are mutually exclusive");
> + return;
> + }
> +
> + /* find the top layer BDS of the chain */
> + bs = bdrv_find(device);
> + if (!bs) {
> + error_set(errp, QERR_DEVICE_NOT_FOUND, device);
> + return;
> + }
> +
> + if (has_image_node_name) {
> + image_bs = bdrv_lookup_bs(NULL, image_node_name, &local_err);
> + if (local_err) {
> + error_propagate(errp, local_err);
> + return;
> + }
> + }
> +
> + if (has_image) {
> + if (!strcmp(bs->filename, image)) {
> + image_bs = bs;
> + } else {
> + image_bs = bdrv_find_backing_image(bs, image);
> + }
> + }
> +
> + if (!has_image && !has_image_node_name) {
> + image_bs = bs;
> + }
> +
> + if (!image_bs) {
> + error_setg(errp, "image file not found");
> + return;
> + }
> +
> + if (bdrv_find_base(image_bs) == image_bs) {
> + error_setg(errp, "not allowing backing file change on an image "
> + "without a backing file");
> + return;
> + }
> +
> + /* even though we are not necessarily operating on bs, we need it to
> + * determine if block ops are currently prohibited on the chain */
> + if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_CHANGE, errp)) {
> + return;
> + }
> +
> + /* final sanity check */
> + if (!bdrv_chain_contains(bs, image_bs)) {
> + error_setg(errp, "'%s' and image file are not in the same chain",
> + device);
> + return;
> + }
> +
> + /* if not r/w, reopen to make r/w */
> + open_flags = image_bs->open_flags;
> + ro = bdrv_is_read_only(image_bs);
> +
> + if (ro) {
> + bdrv_reopen(image_bs, open_flags | BDRV_O_RDWR, &local_err);
> + if (local_err) {
> + error_propagate(errp, local_err);
> + return;
> + }
> + }
> +
> + ret = bdrv_change_backing_file(image_bs, backing_file,
> + image_bs->drv ? image_bs->drv->format_name :
> "");
> +
> + if (ret < 0) {
> + error_setg_errno(errp, -ret, "Could not change backing file to '%s'",
> + backing_file);
> + /* don't exit here, so we can try to restore open flags if
> + * appropriate */
> + }
> +
> + if (ro) {
> + bdrv_reopen(image_bs, open_flags, &local_err);
> + if (local_err) {
> + error_propagate(errp, local_err); /* will preserve prior errp */
> + }
> + }
> +}
> +
> void qmp_blockdev_add(BlockdevOptions *options, Error **errp)
> {
> QmpOutputVisitor *ov = qmp_output_visitor_new();
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index c76d45d..0939143 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -680,6 +680,66 @@
> 'data': 'BlockdevSnapshot' }
>
> ##
> +# @change-backing-file
> +#
> +# Change the backing file in the image file metadata. This does not cause
> QEMU
> +# to reopen the image file to reparse the backing filename (it may, however,
> +# perform a reopen to change permissions from r/o -> r/w -> r/o, if needed).
> +# The new backing file string is written into the image file metadata, and
> the
> +# QEMU internal strings are updated.
> +#
> +# The image file to perform the operation on can be specified by two
> different
> +# methods:
> +#
> +# Method 1: Supply the device name (e.g. 'virtio0'), and optionally the
> image
> +# filename. This would use arguments @device and @image.
> +#
> +# Method 2: Supply the device name, and the node-name of the image to
> modify,
> +# via @image-node-name.
> +#
> +# Arguments @image and @image-node-name are mutually exclusive.
> +#
> +# Method 1 interface
> +#---------------------
> +# @image: #optional The file name of the image to modify. If
> omitted,
> +# and @image-node-name is not supplied, then the
> +# default is the active layer of the chain
> described
> +# by @device.
> +#
> +# Method 2 interface
> +#---------------------
> +# @image-node-name #optional The name of the block driver state node of the
> +# image to modify. The @device argument is used
> to
> +# verify @image-node-name is in the chain
> described
> +# by @device.
> +#
> +# Common arguments
> +#---------------------
> +# @device: The name of the device.
> +#
> +# @backing-file: The string to write as the backing file. This string is
> +# not validated, so care should be taken when specifying
> +# the string or the image chain may not be able to be
> +# reopened again.
> +#
> +# If a pathname string is such that it cannot be
> +# resolved by QEMU, that means that subsequent QMP or
> +# HMP commands must use node-names for the image in
> +# question, as filename lookup methods will fail.
> +#
> +#
> +# Returns: Nothing on success
> +# If @device does not exist or cannot be determined, DeviceNotFound
> +# If @image is specified, but not @device, GenericError
> +# If both @image and @image-node-name are specified, GenericError
> +#
> +# Since: 2.1
> +##
> +{ 'command': 'change-backing-file',
> + 'data': { 'device': 'str', '*image': 'str', '*image-node-name': 'str',
> + 'backing-file': 'str' } }
> +
> +##
> # @block-commit
> #
> # Live commit of data from overlay image nodes into backing nodes - i.e.,
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index 314cbba..c1cbfd2 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -1438,6 +1438,80 @@ Example:
> EQMP
>
> {
> + .name = "change-backing-file",
> + .args_type = "device:s,image:s?,image-node-name:s?,backing-file:s",
> + .mhandler.cmd_new = qmp_marshal_input_change_backing_file,
> + },
> +
> +SQMP
> +change-backing-file
> +-------------------
> +Since: 2.1
> +
> +Change the backing file in the image file metadata. This does not cause QEMU
> +to reopen the image file to reparse the backing filename (it may, however,
> +perform a reopen to change permissions from r/o -> r/w -> r/o, if needed).
> +The new backing file string is written into the image file metadata, and the
> +QEMU internal strings are updated.
> +
> +The image file to perform the operation on can be specified by two different
> +methods:
> +
> + Method 1: Supply the device name (e.g. 'virtio0'), and optionally the image
> + filename. This would use arguments "device" and "image".
> +
> + Method 2: Supply the device name, and the node-name of the image to modify,
> + via "image-node-name".
> +
> +Arguments:
> +
> +Arguments "image" or "image-node-name" are mutually exclusive.
> +
> +
> +Method 1 interface
> +--------------------
> +- "image": The file name of the image to modify. If omitted,
> + and "image-node-name" is not supplied, then the
> + default is the active layer of the chain described
> + by device.
> + (json-string, optional)
> +
> +
> +Method 2 interface
> +--------------------
> +- "image-node-name": The name of the block driver state node of the
> + image to modify. The "device" is argument is used to
> + verify "image-node-name" is in the chain described by
> + "device".
> + (json-string, optional)
> +
> +
> +Common arguments
> +--------------------
> +- "device": The name of the device.
> + (json-string)
> +
> +- "backing-file": The string to write as the backing file. This
> string is
> + not validated, so care should be taken when
> specifying
> + the string or the image chain may not be able to be
> + reopened again.
> + (json-string)
> +
> + If a pathname string is such that it cannot be
> + resolved by QEMU, that means that subsequent QMP or
> + HMP commands must use node-names for the image in
> + question, as filename lookup methods will fail.
> +
> +
> +Returns: Nothing on success
> + If "device" does not exist or cannot be determined, DeviceNotFound
> + If "image" is specified, but not "device, GenericError
> + If both "image" and "image-node-name" are specified, GenericError
> +
> +
> +EQMP
> +
> + {
> .name = "balloon",
> .args_type = "value:M",
> .mhandler.cmd_new = qmp_marshal_input_balloon,
> --
> 1.9.3
>
Could you provide an example script of how these backing file manipulation
are suposed to be done ?
Best regards
Benoît
- [Qemu-devel] [PATCH v6 for 2.1 06/10] block: extend block-commit to accept a string for the backing file, (continued)
- [Qemu-devel] [PATCH v6 for 2.1 06/10] block: extend block-commit to accept a string for the backing file, Jeff Cody, 2014/06/17
- [Qemu-devel] [PATCH v6 for 2.1 07/10] block: add ability for block-stream to use node-name, Jeff Cody, 2014/06/17
- [Qemu-devel] [PATCH v6 for 2.1 08/10] block: add backing-file option to block-stream, Jeff Cody, 2014/06/17
- [Qemu-devel] [PATCH v6 for 2.1 09/10] block: Add QMP documentation for block-stream, Jeff Cody, 2014/06/17
- [Qemu-devel] [PATCH v6 for 2.1 10/10] block: add QAPI command to allow live backing file change, Jeff Cody, 2014/06/17
- Re: [Qemu-devel] [PATCH v6 for 2.1 10/10] block: add QAPI command to allow live backing file change,
Benoît Canet <=
- Re: [Qemu-devel] [PATCH v6 for 2.1 10/10] block: add QAPI command to allow live backing file change, Stefan Hajnoczi, 2014/06/19
- Re: [Qemu-devel] [PATCH v6 for 2.1 00/10] Modify block jobs to use node-names, Stefan Hajnoczi, 2014/06/19