linux-user: Add support for a group of btrfs inode ioctls

linux-user: Add support for a group of btrfs inode ioctls

This patch implements functionality of following ioctls:

BTRFS_IOC_INO_LOOKUP - Reading tree root id and path

    Read tree root id and path for a given file or directory.
    The name and tree root id are returned in an ioctl's third
    argument that represents a pointer to a following type:

    struct btrfs_ioctl_ino_lookup_args {
	__u64 treeid;
	__u64 objectid;
	char name[BTRFS_INO_LOOKUP_PATH_MAX];
    };

    Before calling this ioctl, field 'objectid' should be filled
    with the object id value for which the tree id and path are
    to be read. Value 'BTRFS_FIRST_FREE_OBJECTID' represents the
    object id for the first available btrfs object (directory or
    file).

BTRFS_IOC_INO_PATHS - Reading paths to all files

    Read path to all files with a certain inode number. The paths
    are returned in the ioctl's third argument which represents
    a pointer to a following type:

    struct btrfs_ioctl_ino_path_args {
	__u64				inum;		/* in */
	__u64				size;		/* in */
	__u64				reserved[4];
	/* struct btrfs_data_container	*fspath;	   out */
	__u64				fspath;		/* out */
     };

     Before calling this ioctl, the 'inum' and 'size' field should
     be filled with the aproppriate inode number and size of the
     directory where file paths should be looked for. For now, the
     paths are returned in an '__u64' (unsigned long long) value
     'fspath'.

BTRFS_IOC_LOGICAL_INO - Reading inode numbers

     Read inode numbers for files on a certain logical adress. The
     inode numbers are returned in the ioctl's third argument which
     represents a pointer to a following type:

     struct btrfs_ioctl_logical_ino_args {
	__u64				logical;	/* in */
	__u64				size;		/* in */
	__u64				reserved[3];	/* must be 0 for now */
	__u64				flags;		/* in, v2 only */
	/* struct btrfs_data_container	*inodes;	out   */
	__u64				inodes;
     };

     Before calling this ioctl, the 'logical' and 'size' field should
     be filled with the aproppriate logical adress and size of where
     the inode numbers of files should be looked for. For now, the
     inode numbers are returned in an '__u64' (unsigned long long)
     value 'inodes'.

BTRFS_IOC_LOGICAL_INO_V2 - Reading inode numbers

     Same as the above mentioned ioctl except that it allows passing
     a flags 'BTRFS_LOGICAL_INO_ARGS_IGNORE_OFFSET'.

BTRFS_IOC_INO_LOOKUP_USER - Reading subvolume name and path

     Read name and path of a subvolume. The tree root id and
     path are read in an ioctl's third argument which represents a
     pointer to a following type:

     struct btrfs_ioctl_ino_lookup_user_args {
	/* in, inode number containing the subvolume of 'subvolid' */
	__u64 dirid;
	/* in */
	__u64 treeid;
	/* out, name of the subvolume of 'treeid' */
	char name[BTRFS_VOL_NAME_MAX + 1];
	/*
	 * out, constructed path from the directory with which the ioctl is
	 * called to dirid
	 */
	char path[BTRFS_INO_LOOKUP_USER_PATH_MAX];
     };

     Before calling this ioctl, the 'dirid' and 'treeid' field should
     be filled with aproppriate values which represent the inode number
     of the directory that contains the subvolume and treeid of the
     subvolume.

Implementation notes:

     All of the ioctls in this patch use structure types as third arguments.
     That is the reason why aproppriate thunk definitions were added in file
     'syscall_types.h'.

Signed-off-by: Filip Bozuta <Filip.Bozuta@syrmia.com>
Tested-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200823195014.116226-6-Filip.Bozuta@syrmia.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>