linux-user: Add support for btrfs ioctls used to manipulate with devices

linux-user: Add support for btrfs ioctls used to manipulate with devices

This patch implements functionality for following ioctls:

BTRFS_IOC_SCAN_DEV - Scanning device for a btrfs filesystem

    Scan a device for a btrfs filesystem. The device that is to
    be scanned is passed in the ioctl's third argument which
    represents a pointer to a 'struct ioc_vol_args' (which was
    mentioned in a previous patch). Before calling this ioctl,
    the name field of this structure should be filled with the
    aproppriate name value which represents a path for the device.
    If the device contains a btrfs filesystem, the ioctl returns 0,
    otherwise a negative value is returned.

BTRFS_IOC_ADD_DEV - Adding a device to a btrfs filesystem

    Add a device to a btrfs filesystem. The device that is to be
    added is passed in the ioctl's third argument which represents
    a pointer to a 'struct ioc_vol_args' (which was mentioned in
    a previous patch). Before calling this ioctl, the name field of
    this structure should be filled with the aproppriate name value
    which represents a path for the device.

BTRFS_IOC_RM_DEV - Removing a device from a btrfs filesystem

    Remove a device from a btrfs filesystem. The device that is to be
    removed is passed in the ioctl's third argument which represents
    a pointer to a 'struct ioc_vol_args' (which was mentioned in
    a previous patch). Before calling this ioctl, the name field of
    this structure should be filled with the aproppriate name value
    which represents a path for the device.

BTRFS_IOC_DEV_INFO - Getting information about a device

    Obtain information for device in a btrfs filesystem. The information
    is gathered in the ioctl's third argument which represents a pointer
    to a following structure type:

    struct btrfs_ioctl_dev_info_args {
	__u64 devid;				/* in/out */
	__u8 uuid[BTRFS_UUID_SIZE];		/* in/out */
	__u64 bytes_used;			/* out */
	__u64 total_bytes;			/* out */
	__u64 unused[379];			/* pad to 4k */
	__u8 path[BTRFS_DEVICE_PATH_NAME_MAX];	/* out */
    };

    Before calling this ioctl, field "devid" should be set with the id value
    for the device for which the information is to be obtained. If this field
    is not aproppriately set, the errno ENODEV ("No such device") is returned.

BTRFS_IOC_GET_DEV_STATS - Getting device statistics

    Obtain stats informatin for device in a btrfs filesystem. The information
    is gathered in the ioctl's third argument which represents a pointer to
    a following structure type:

    struct btrfs_ioctl_get_dev_stats {
	__u64 devid;				/* in */
	__u64 nr_items;				/* in/out */
	__u64 flags;				/* in/out */

	/* out values: */
	__u64 values[BTRFS_DEV_STAT_VALUES_MAX];

	/*
	 * This pads the struct to 1032 bytes. It was originally meant to pad to
	 * 1024 bytes, but when adding the flags field, the padding calculation
	 * was not adjusted.
	 */
	__u64 unused[128 - 2 - BTRFS_DEV_STAT_VALUES_MAX];
    };

    Before calling this ioctl, field "devid" should be set with the id value
    for the device for which the information is to be obtained. If this field
    is not aproppriately set, the errno ENODEV ("No such device") is returned.

BTRFS_IOC_FORGET_DEV - Remove unmounted devices

    Search and remove all stale devices (devices which are not mounted).
    The third ioctl argument is a pointer to a 'struct btrfs_ioctl_vol_args'.
    The ioctl call will release all unmounted devices which match the path
    which is specified in the "name" field of the structure. If an empty
    path ("") is specified, all unmounted devices will be released.

Implementation notes:

    Ioctls BTRFS_IOC_DEV_INFO and BTRFS_IOC_GET_DEV_STATS use types
    'struct btrfs_ioctl_dev_info_args' and ' struct btrfs_ioctl_get_dev_stats'
    as third argument types. That is the reason why corresponding structure
    definitions were added in file 'linux-user/syscall_types.h'.
    Since the thunk type for 'struct ioc_vol_args' was already added in a
    previous patch, the rest of the implementation was straightforward.

Signed-off-by: Filip Bozuta <Filip.Bozuta@syrmia.com>
Tested-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200823195014.116226-4-Filip.Bozuta@syrmia.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>