write error can't recover even the error condition is gone

[qingyunha]

I notice fileWriter.Write return fileWriter.err and fileWriter.err never clear after it be assigned a errror value.

[davies]

When there is an error during writing, which means some data is already lost, it can't recover the lost data so the error should not be cleared.

[qingyunha]

Considing this scenario, a long runing process that attempts to write to a log file but encounters a no space left error should succeed after the disk has enough space.