About Filesystem freeze/thaw in freebsd

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 Hi,               I am experimenting to do a live backup of FreeBSD VM. Question is do we have freeze/thaw interfaces in FreeBSD? I searched a lot in web and freebsd source code, just could not find the right interface.               As I know that in linux:VxFS provides ioctl interfaces to application programs to freeze and thaw VxFS file systems. The interfaces are VX_FREEZE, VX_FREEZE_ALL, and VX_THAW.About Freeze and thaw Freezing a file system temporarily blocks all I/O operations to a file system and then performs a sync on the file system. Current operations are completed and the file system is synchronized to disk. Freezing a file system is a necessary step for obtaining a stable and consistent image of the file system at the volume level. Consistent volume-level file system images can be obtained and used with a file system snapshot tool. The freeze operation flushes all buffers and pages in the file system cache that contain dirty metadata and user data. The operation then suspends any new activity on the file system until the file system is thawed.             Any help would be appreciated, thanks a lot!  Andy Zhang