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[dm-devel] [RFC] device-mapper ioctl interface



Here's the header file for the the proposed new ioctl interface for
dm.  We've tried to change as little as possible to minimise code
changes in LVM2 and EVMS.

The changes address the following problems:

o) Alignment mistakes in the ioctl structures

o) Provide a way for the userland tools to back out of a series of
   table updates without having to reload the orginal tables (remember
   that an LV is often composed of a stack of 2 or more dm devices).

o) Pre-loading of a new table may now occur without suspending the
   device.  (Table loading can potentially allocate a lot of memory,
   eg. mirror buffers).

o) Minimise the amount of time that a device is suspended.  eg. if a
   simple linear mapping is being extended, there is no longer a need to
   call the suspend ioctl in between the table load and the resume.
   Instead the resume (which swaps in the new table), will do the right
   thing.

- Joe
/*
 * Copyright (C) 2001, 2003 Sistina Software (UK) Limited.
 *
 * This file is released under the LGPL.
 */

#ifndef _LINUX_DM_IOCTL_H
#define _LINUX_DM_IOCTL_H

#include <linux/types.h>

#define DM_DIR "mapper"	/* Slashes not supported */
#define DM_MAX_TYPE_NAME 16
#define DM_NAME_LEN 128
#define DM_UUID_LEN 129

/*
 * A traditional ioctl interface for the device mapper.
 *
 * Each device can have two tables associated with it, an
 * 'active' table which is the one currently used by io passing
 * through the device, and an 'inactive' one which is a table
 * that is being prepared as a replacement for the 'active' one.
 *
 * DM_VERSION:
 * Just get the version information for the ioctl interface.
 *
 * DM_REMOVE_ALL:
 * Remove all dm devices, destroy all tables.  Only really used
 * for debug.
 *
 * DM_LIST_DEVICES:
 * Get a list of all the dm device names.
 *
 * DM_DEV_CREATE:
 * Create a new device, neither the 'active' or 'inactive' table
 * slots will be filled.  The device will be in suspended state
 * after creation, however any io to the device will get errored
 * since it will be out-of-bounds.
 *
 * DM_DEV_REMOVE:
 * Remove a device, destroy any tables.
 *
 * DM_DEV_RENAME:
 * Rename a device.
 *
 * DM_SUSPEND:
 * This performs both suspend and resume, depending which flag is
 * passed in.
 * Suspend: This command will not return until all pending io to
 * the device has completed.  Further io will be deferred until
 * the device is resumed.
 * Resume: It is no longer an error to issue this command on an
 * unsuspended device.  If a table is present in the 'inactive'
 * slot, it will be moved to the active slot, then the old table
 * from the active slot will be _destroyed_.  Finally the device
 * is resumed.
 *
 * DM_DEV_STATUS:
 * Retrieves the status for the table in the 'active' slot.
 *
 * DM_DEV_WAIT:
 * Wait for a significant event to occur to the device.  This
 * could either be caused by an event triggered by one of the
 * targets of the table in the 'active' slot, or a table change.
 *
 * DM_TABLE_LOAD:
 * Load a table into the 'inactive' slot for the device.  The
 * device does _not_ need to be suspended prior to this command.
 *
 * DM_TABLE_CLEAR:
 * Destroy any table in the 'inactive' slot (ie. abort).
 *
 * DM_TABLE_DEPS:
 * Return a set of device dependencies for the 'active' table.
 *
 * DM_TABLE_STATUS:
 * Return the targets status for the 'active' table.
 */

/*
 * All ioctl arguments consist of a single chunk of memory, with
 * this structure at the start.  If a uuid is specified any
 * lookup (eg. for a DM_INFO) will be done on that, *not* the
 * name.
 */
struct dm_ioctl {
	/*
	 * The version number is made up of three parts:
	 * major - no backward or forward compatibility,
	 * minor - only backwards compatible,
	 * patch - both backwards and forwards compatible.
	 *
	 * All clients of the ioctl interface should fill in the
	 * version number of the interface that they were
	 * compiled with.
	 *
	 * All recognised ioctl commands (ie. those that don't
	 * return -ENOTTY) fill out this field, even if the
	 * command failed.
	 */
	uint32_t version[3];	/* in/out */
	uint32_t data_size;	/* total size of data passed in
				 * including this struct */

	uint32_t data_start;	/* offset to start of data
				 * relative to start of this struct */

	uint32_t target_count;	/* in/out */
	int32_t open_count;	/* out */
	uint32_t flags;		/* in/out */
	uint32_t event_nr;      /* in/out */
	uint32_t padding;

	uint64_t dev;		/* in/out */

	char name[DM_NAME_LEN];	/* device name */
	char uuid[DM_UUID_LEN];	/* unique identifier for
				 * the block device */
};

/*
 * Used to specify tables.  These structures appear after the
 * dm_ioctl.
 */
struct dm_target_spec {
	uint64_t sector_start;
	uint64_t length;
	int32_t status;		/* used when reading from kernel only */

	/*
	 * Offset in bytes (from the start of this struct) to
	 * next target_spec.
	 */
	uint32_t next;

	char target_type[DM_MAX_TYPE_NAME];

	/*
	 * Parameter string starts immediately after this object.
	 * Be careful to add padding after string to ensure correct
	 * alignment of subsequent dm_target_spec.
	 */
};

/*
 * Used to retrieve the target dependencies.
 */
struct dm_target_deps {
	uint32_t count;		/* Array size */
	uint32_t padding;	/* unused */
	uint64_t dev[0];	/* out */
};

/*
 * Used to get a list of all dm devices.
 */
struct dm_name_list {
	uint64_t dev;
	uint32_t next;		/* offset to the next record from
				   the _start_ of this */
	char name[0];
};

/*
 * If you change this make sure you make the corresponding change
 * to dm-ioctl.c:lookup_ioctl()
 */
enum {
	/* Top level cmds */
	DM_VERSION_CMD = 0,
	DM_REMOVE_ALL_CMD,
	DM_LIST_DEVICES_CMD,

	/* device level cmds */
	DM_DEV_CREATE_CMD,
	DM_DEV_REMOVE_CMD,
	DM_DEV_RENAME_CMD,
	DM_DEV_SUSPEND_CMD,
	DM_DEV_STATUS_CMD,
	DM_DEV_WAIT_CMD,

	/* Table level cmds */
	DM_TABLE_LOAD_CMD,
	DM_TABLE_CLEAR_CMD,
	DM_TABLE_DEPS_CMD,
	DM_TABLE_STATUS_CMD,
};

#define DM_IOCTL 0xfd

#define DM_VERSION       _IOWR(DM_IOCTL, DM_VERSION_CMD, struct dm_ioctl)
#define DM_REMOVE_ALL    _IOWR(DM_IOCTL, DM_REMOVE_ALL_CMD, struct dm_ioctl)
#define DM_LIST_DEVICES  _IOWR(DM_IOCTL, DM_LIST_DEVICES_CMD, struct dm_ioctl)

#define DM_DEV_CREATE    _IOWR(DM_IOCTL, DM_DEV_CREATE_CMD, struct dm_ioctl)
#define DM_DEV_REMOVE    _IOWR(DM_IOCTL, DM_DEV_REMOVE_CMD, struct dm_ioctl)
#define DM_DEV_RENAME    _IOWR(DM_IOCTL, DM_DEV_RENAME_CMD, struct dm_ioctl)
#define DM_DEV_SUSPEND   _IOWR(DM_IOCTL, DM_DEV_SUSPEND_CMD, struct dm_ioctl)
#define DM_DEV_STATUS    _IOWR(DM_IOCTL, DM_DEV_STATUS_CMD, struct dm_ioctl)
#define DM_DEV_WAIT      _IOWR(DM_IOCTL, DM_DEV_WAIT_CMD, struct dm_ioctl)

#define DM_TABLE_LOAD    _IOWR(DM_IOCTL, DM_TABLE_LOAD_CMD, struct dm_ioctl)
#define DM_TABLE_CLEAR   _IOWR(DM_IOCTL, DM_TABLE_CLEAR_CMD, struct dm_ioctl)
#define DM_TABLE_DEPS    _IOWR(DM_IOCTL, DM_TABLE_DEPS_CMD, struct dm_ioctl)
#define DM_TABLE_STATUS  _IOWR(DM_IOCTL, DM_TABLE_STATUS_CMD, struct dm_ioctl)

#define DM_VERSION_MAJOR	4
#define DM_VERSION_MINOR	0
#define DM_VERSION_PATCHLEVEL	0
#define DM_VERSION_EXTRA	"-ioctl-cvs (2003-06-04)"

/* Status bits */
#define DM_READONLY_FLAG	(1 << 0) /* In/Out */
#define DM_SUSPEND_FLAG		(1 << 1) /* In/Out */
#define DM_PERSISTENT_DEV_FLAG	(1 << 3) /* In */

/*
 * Flag passed into ioctl STATUS command to get table information
 * rather than current status.
 */
#define DM_STATUS_TABLE_FLAG	(1 << 4) /* In */

/*
 * Flags that indicate whether a table is present in either of
 * the two table slots that a device has.
 */
#define DM_ACTIVE_PRESENT_FLAG   (1 << 5) /* Out */
#define DM_INACTIVE_PRESENT_FLAG (1 << 6) /* Out */

/*
 * Indicates that the buffer passed in wasn't big enough for the
 * results.
 */
#define DM_BUFFER_FULL_FLAG	(1 << 8) /* Out */

#endif				/* _LINUX_DM_IOCTL_H */

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