bvar导出到全局统一路径

如果假设线上都是work账号的号，可以导出到~/bvar_monitor//bvar.data。这样监控系统只要扫描/home/work/bvar_monitor下的所有子目录就好了。

Start by locating the bvar export implementation and the code that writes bvar.data. Trace how the current output path is selected, then verify that exports use the proposed ~/bvar_monitor//bvar.data layout and remain discoverable by scanning /home/work/bvar_monitor subdirectories.

Written by the indexing model from the issue text.