Function snapshot_create 

pub fn snapshot_create(
    parent_fd: BorrowedFd<'_>,
    source_fd: BorrowedFd<'_>,
    name: &CStr,
    readonly: bool,
    qgroups: &[u64],
) -> Result<()>

Create a snapshot of the subvolume referred to by source_fd, placing it as name inside the directory referred to by parent_fd.

If readonly is true the new snapshot is created read-only. If qgroups is non-empty, the new snapshot is added to those qgroups. Requires CAP_SYS_ADMIN.

Errors: ENAMETOOLONG if name does not fit in the 4040-byte kernel buffer. EEXIST if a subvolume or directory with that name already exists. EROFS if parent_fd refers to a read-only subvolume. EPERM without CAP_SYS_ADMIN.

Errors

Returns Err if the ioctl fails.