Unable to set general log to fifo pipe
It looks like it should work because the general_log_file is dynamic (according to the MySQL Documentation).

Some six(6) years ago, Joel Hanger answered How do I output MySQL logs to syslog?. In his answer, he added it to the my.cnf. Evidently, a mysqld restart would be needed.

In your particular case, you may have to enable the general log first using

SET GLOBAL general_log = 1;


to initiate a general log with the default name of hostname.log.

This will create an open file handle. You may then have to try setting the general_log_file with general_log on and off. You may also have to run FLUSH LOGS; to force the closing and reopening of log file handles.

This answer is just a lazy guess, so try it and see.