[PATCH v4 04/11] blksnap: header file of the module interface

[Sergei Shtepa]

The header file contains a set of declarations, structures and control
requests (ioctl) that allows to manage the module from the user space.

Co-developed-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Tested-by: Donald Buczek <buczek@xxxxxxxxxxxxx>
Signed-off-by: Sergei Shtepa <sergei.shtepa@xxxxxxxxx>
---
 MAINTAINERS                  |   1 +
 include/uapi/linux/blksnap.h | 421 +++++++++++++++++++++++++++++++++++
 2 files changed, 422 insertions(+)
 create mode 100644 include/uapi/linux/blksnap.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 408e0df0a3c6..1cbd551d3897 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3597,6 +3597,7 @@ M:	Sergei Shtepa <sergei.shtepa@xxxxxxxxx>
 L:	linux-block@xxxxxxxxxxxxxxx
 S:	Supported
 F:	Documentation/block/blksnap.rst
+F:	include/uapi/linux/blksnap.h

 BLOCK LAYER
 M:	Jens Axboe <axboe@xxxxxxxxx>
diff --git a/include/uapi/linux/blksnap.h b/include/uapi/linux/blksnap.h
new file mode 100644
index 000000000000..2fe3f2a43bc5
--- /dev/null
+++ b/include/uapi/linux/blksnap.h
@@ -0,0 +1,421 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/* Copyright (C) 2023 Veeam Software Group GmbH */
+#ifndef _UAPI_LINUX_BLKSNAP_H
+#define _UAPI_LINUX_BLKSNAP_H
+
+#include <linux/types.h>
+
+#define BLKSNAP_CTL "blksnap-control"
+#define BLKSNAP_IMAGE_NAME "blksnap-image"
+#define BLKSNAP 'V'
+
+/**
+ * DOC: Block device filter interface.
+ *
+ * Control commands that are transmitted through the block device filter
+ * interface.
+ */
+
+/**
+ * enum blkfilter_ctl_blksnap - List of commands for BLKFILTER_CTL ioctl
+ *
+ * @blkfilter_ctl_blksnap_cbtinfo:
+ *	Get CBT information.
+ *	The result of executing the command is a &struct blksnap_cbtinfo.
+ *	Return 0 if succeeded, negative errno otherwise.
+ * @blkfilter_ctl_blksnap_cbtmap:
+ *	Read the CBT map.
+ *	The option passes the &struct blksnap_cbtmap.
+ *	The size of the table can be quite large. Thus, the table is read in
+ *	a loop, in each cycle of which the next offset is set to
+ *	&blksnap_tracker_read_cbt_bitmap.offset.
+ *	Return a count of bytes read if succeeded, negative errno otherwise.
+ * @blkfilter_ctl_blksnap_cbtdirty:
+ *	Set dirty blocks in the CBT map.
+ *	The option passes the &struct blksnap_cbtdirty.
+ *	There are cases when some blocks need to be marked as changed.
+ *	This ioctl allows to do this.
+ *	Return 0 if succeeded, negative errno otherwise.
+ * @blkfilter_ctl_blksnap_snapshotadd:
+ *	Add device to snapshot.
+ *	The option passes the &struct blksnap_snapshotadd.
+ *	Return 0 if succeeded, negative errno otherwise.
+ * @blkfilter_ctl_blksnap_snapshotinfo:
+ *	Get information about snapshot.
+ *	The result of executing the command is a &struct blksnap_snapshotinfo.
+ *	Return 0 if succeeded, negative errno otherwise.
+ */
+enum blkfilter_ctl_blksnap {
+	blkfilter_ctl_blksnap_cbtinfo,
+	blkfilter_ctl_blksnap_cbtmap,
+	blkfilter_ctl_blksnap_cbtdirty,
+	blkfilter_ctl_blksnap_snapshotadd,
+	blkfilter_ctl_blksnap_snapshotinfo,
+};
+
+#ifndef UUID_SIZE
+#define UUID_SIZE 16
+#endif
+
+/**
+ * struct blksnap_uuid - Unique 16-byte identifier.
+ *
+ * @b:
+ *	An array of 16 bytes.
+ */
+struct blksnap_uuid {
+	__u8 b[UUID_SIZE];
+};
+
+/**
+ * struct blksnap_cbtinfo - Result for the command
+ *	&blkfilter_ctl_blksnap.blkfilter_ctl_blksnap_cbtinfo.
+ *
+ * @device_capacity:
+ *	Device capacity in bytes.
+ * @block_size:
+ *	Block size in bytes.
+ * @block_count:
+ *	Number of blocks.
+ * @generation_id:
+ *	Unique identifier of change tracking generation.
+ * @changes_number:
+ *	Current changes number.
+ */
+struct blksnap_cbtinfo {
+	__u64 device_capacity;
+	__u32 block_size;
+	__u32 block_count;
+	struct blksnap_uuid generation_id;
+	__u8 changes_number;
+};
+
+/**
+ * struct blksnap_cbtmap - Option for the command
+ *	&blkfilter_ctl_blksnap.blkfilter_ctl_blksnap_cbtmap.
+ *
+ * @offset:
+ *	Offset from the beginning of the CBT bitmap in bytes.
+ * @length:
+ *	Size of @buffer in bytes.
+ * @buffer:
+ *	Pointer to the buffer for output.
+ */
+struct blksnap_cbtmap {
+	__u32 offset;
+	__u32 length;
+	__u64 buffer;
+};
+
+/**
+ * struct blksnap_sectors - Description of the block device region.
+ *
+ * @offset:
+ *	Offset from the beginning of the disk in sectors.
+ * @count:
+ *	Count of sectors.
+ */
+struct blksnap_sectors {
+	__u64 offset;
+	__u64 count;
+};
+
+/**
+ * struct blksnap_cbtdirty - Option for the command
+ *	&blkfilter_ctl_blksnap.blkfilter_ctl_blksnap_cbtdirty.
+ *
+ * @count:
+ *	Count of elements in the @dirty_sectors.
+ * @dirty_sectors:
+ *	Pointer to the array of &struct blksnap_sectors.
+ */
+struct blksnap_cbtdirty {
+	__u32 count;
+	__u64 dirty_sectors;
+};
+
+/**
+ * struct blksnap_snapshotadd - Option for the command
+ *	&blkfilter_ctl_blksnap.blkfilter_ctl_blksnap_snapshotadd.
+ *
+ * @id:
+ *	ID of the snapshot to which the block device should be added.
+ */
+struct blksnap_snapshotadd {
+	struct blksnap_uuid id;
+};
+
+#define IMAGE_DISK_NAME_LEN 32
+
+/**
+ * struct blksnap_snapshotinfo - Result for the command
+ *	&blkfilter_ctl_blksnap.blkfilter_ctl_blksnap_snapshotinfo.
+ *
+ * @error_code:
+ *	Zero if there were no errors while holding the snapshot.
+ *	The error code -ENOSPC means that while holding the snapshot, a snapshot
+ *	overflow situation has occurred. Other error codes mean other reasons
+ *	for failure.
+ *	The error code is reset when the device is added to a new snapshot.
+ * @image:
+ *	If the snapshot was taken, it stores the block device name of the
+ *	image, or empty string otherwise.
+ */
+struct blksnap_snapshotinfo {
+	__s32 error_code;
+	__u8 image[IMAGE_DISK_NAME_LEN];
+};
+
+/**
+ * DOC: Interface for managing snapshots
+ *
+ * Control commands that are transmitted through the blksnap module interface.
+ */
+enum blksnap_ioctl {
+	blksnap_ioctl_version,
+	blksnap_ioctl_snapshot_create,
+	blksnap_ioctl_snapshot_destroy,
+	blksnap_ioctl_snapshot_append_storage,
+	blksnap_ioctl_snapshot_take,
+	blksnap_ioctl_snapshot_collect,
+	blksnap_ioctl_snapshot_wait_event,
+};
+
+/**
+ * struct blksnap_version - Module version.
+ *
+ * @major:
+ *	Version major part.
+ * @minor:
+ *	Version minor part.
+ * @revision:
+ *	Revision number.
+ * @build:
+ *	Build number. Should be zero.
+ */
+struct blksnap_version {
+	__u16 major;
+	__u16 minor;
+	__u16 revision;
+	__u16 build;
+};
+
+/**
+ * define IOCTL_BLKSNAP_VERSION - Get module version.
+ *
+ * The version may increase when the API changes. But linking the user space
+ * behavior to the version code does not seem to be a good idea.
+ * To ensure backward compatibility, API changes should be made by adding new
+ * ioctl without changing the behavior of existing ones. The version should be
+ * used for logs.
+ *
+ * Return: 0 if succeeded, negative errno otherwise.
+ */
+#define IOCTL_BLKSNAP_VERSION							\
+	_IOW(BLKSNAP, blksnap_ioctl_version, struct blksnap_version)
+
+
+/**
+ * define IOCTL_BLKSNAP_SNAPSHOT_CREATE - Create snapshot.
+ *
+ * Creates a snapshot structure in the memory and allocates an identifier for
+ * it. Further interaction with the snapshot is possible by this identifier.
+ * A snapshot is created for several block devices at once.
+ * Several snapshots can be created at the same time, but with the condition
+ * that one block device can only be included in one snapshot.
+ *
+ * Return: 0 if succeeded, negative errno otherwise.
+ */
+#define IOCTL_BLKSNAP_SNAPSHOT_CREATE						\
+	_IOW(BLKSNAP, blksnap_ioctl_snapshot_create,				\
+	     struct blksnap_uuid)
+
+
+/**
+ * define IOCTL_BLKSNAP_SNAPSHOT_DESTROY - Release and destroy the snapshot.
+ *
+ * Destroys snapshot with &blksnap_snapshot_destroy.id. This leads to the
+ * deletion of all block device images of the snapshot. The difference storage
+ * is being released. But the change tracker keeps tracking.
+ *
+ * Return: 0 if succeeded, negative errno otherwise.
+ */
+#define IOCTL_BLKSNAP_SNAPSHOT_DESTROY						\
+	_IOR(BLKSNAP, blksnap_ioctl_snapshot_destroy,				\
+	     struct blksnap_uuid)
+
+/**
+ * struct blksnap_snapshot_append_storage - Argument for the
+ *	&IOCTL_BLKSNAP_SNAPSHOT_APPEND_STORAGE control.
+ *
+ * @id:
+ *	Snapshot ID.
+ * @bdev_path:
+ *	Device path string buffer.
+ * @bdev_path_size:
+ *	Device path string buffer size.
+ * @count:
+ *	Size of @ranges in the number of &struct blksnap_sectors.
+ * @ranges:
+ *	Pointer to the array of &struct blksnap_sectors.
+ */
+struct blksnap_snapshot_append_storage {
+	struct blksnap_uuid id;
+	__u64 bdev_path;
+	__u32 bdev_path_size;
+	__u32 count;
+	__u64 ranges;
+};
+
+/**
+ * define IOCTL_BLKSNAP_SNAPSHOT_APPEND_STORAGE - Append storage to the
+ *	difference storage of the snapshot.
+ *
+ * The snapshot difference storage can be set either before or after creating
+ * the snapshot images. This allows to dynamically expand the difference
+ * storage while holding the snapshot.
+ *
+ * Return: 0 if succeeded, negative errno otherwise.
+ */
+#define IOCTL_BLKSNAP_SNAPSHOT_APPEND_STORAGE					\
+	_IOW(BLKSNAP, blksnap_ioctl_snapshot_append_storage,			\
+	     struct blksnap_snapshot_append_storage)
+
+/**
+ * define IOCTL_BLKSNAP_SNAPSHOT_TAKE - Take snapshot.
+ *
+ * Creates snapshot images of block devices and switches change trackers tables.
+ * The snapshot must be created before this call, and the areas of block
+ * devices should be added to the difference storage.
+ *
+ * Return: 0 if succeeded, negative errno otherwise.
+ */
+#define IOCTL_BLKSNAP_SNAPSHOT_TAKE						\
+	_IOR(BLKSNAP, blksnap_ioctl_snapshot_take,				\
+	     struct blksnap_uuid)
+
+/**
+ * struct blksnap_snapshot_collect - Argument for the
+ *	&IOCTL_BLKSNAP_SNAPSHOT_COLLECT control.
+ *
+ * @count:
+ *	Size of &blksnap_snapshot_collect.ids in the number of 16-byte UUID.
+ * @ids:
+ *	Pointer to the array of struct blksnap_uuid for output.
+ */
+struct blksnap_snapshot_collect {
+	__u32 count;
+	__u64 ids;
+};
+
+/**
+ * define IOCTL_BLKSNAP_SNAPSHOT_COLLECT - Get collection of created snapshots.
+ *
+ * Multiple snapshots can be created at the same time. This allows for one
+ * system to create backups for different data with a independent schedules.
+ *
+ * If in &blksnap_snapshot_collect.count is less than required to store the
+ * &blksnap_snapshot_collect.ids, the array is not filled, and the ioctl
+ * returns the required count for &blksnap_snapshot_collect.ids.
+ *
+ * So, it is recommended to call the ioctl twice. The first call with an null
+ * pointer &blksnap_snapshot_collect.ids and a zero value in
+ * &blksnap_snapshot_collect.count. It will set the required array size in
+ * &blksnap_snapshot_collect.count. The second call with a pointer
+ * &blksnap_snapshot_collect.ids to an array of the required size will allow to
+ * get collection of active snapshots.
+ *
+ * Return: 0 if succeeded, -ENODATA if there is not enough space in the array
+ * to store collection of active snapshots, or negative errno otherwise.
+ */
+#define IOCTL_BLKSNAP_SNAPSHOT_COLLECT						\
+	_IOW(BLKSNAP, blksnap_ioctl_snapshot_collect,				\
+	     struct blksnap_snapshot_collect)
+
+/**
+ * enum blksnap_event_codes - Variants of event codes.
+ *
+ * @blksnap_event_code_low_free_space:
+ *	Low free space in difference storage event.
+ *	If the free space in the difference storage is reduced to the specified
+ *	limit, the module generates this event.
+ * @blksnap_event_code_corrupted:
+ *	Snapshot image is corrupted event.
+ *	If a chunk could not be allocated when trying to save data to the
+ *	difference storage, this event is generated. However, this does not mean
+ *	that the backup process was interrupted with an error. If the snapshot
+ *	image has been read to the end by this time, the backup process is
+ *	considered successful.
+ */
+enum blksnap_event_codes {
+	blksnap_event_code_low_free_space,
+	blksnap_event_code_corrupted,
+};
+
+/**
+ * struct blksnap_snapshot_event - Argument for the
+ *	&IOCTL_BLKSNAP_SNAPSHOT_WAIT_EVENT control.
+ *
+ * @id:
+ *	Snapshot ID.
+ * @timeout_ms:
+ *	Timeout for waiting in milliseconds.
+ * @code:
+ *      Code of the received event &enum blksnap_event_codes.
+ * @time_label:
+ *	Timestamp of the received event.
+ * @data:
+ *	The received event body.
+ */
+struct blksnap_snapshot_event {
+	struct blksnap_uuid id;
+	__u32 timeout_ms;
+	__u32 code;
+	__s64 time_label;
+	__u8 data[4096 - 32];
+};
+
+/**
+ * define IOCTL_BLKSNAP_SNAPSHOT_WAIT_EVENT - Wait and get the event from the
+ *	snapshot.
+ *
+ * While holding the snapshot, the kernel module can transmit information about
+ * changes in its state in the form of events to the user level.
+ * It is very important to receive these events as quickly as possible, so the
+ * user's thread is in the state of interruptable sleep.
+ *
+ * Return: 0 if succeeded, negative errno otherwise.
+ */
+#define IOCTL_BLKSNAP_SNAPSHOT_WAIT_EVENT					\
+	_IOW(BLKSNAP, blksnap_ioctl_snapshot_wait_event,			\
+	     struct blksnap_snapshot_event)
+
+/**
+ * struct blksnap_event_low_free_space - Data for the
+ *	&blksnap_event_code_low_free_space event.
+ *
+ * @requested_nr_sect:
+ *	The required number of sectors.
+ */
+struct blksnap_event_low_free_space {
+	__u64 requested_nr_sect;
+};
+
+/**
+ * struct blksnap_event_corrupted - Data for the
+ *	&blksnap_event_code_corrupted event.
+ *
+ * @dev_id_mj:
+ *	Major part of original device ID.
+ * @dev_id_mn:
+ *	Minor part of original device ID.
+ * @err_code:
+ *	Error code.
+ */
+struct blksnap_event_corrupted {
+	__u32 dev_id_mj;
+	__u32 dev_id_mn;
+	__s32 err_code;
+};
+
+#endif /* _UAPI_LINUX_BLKSNAP_H */
--
2.20.1