linux里I/O操作的通用error code，调用fclose(fd)调用返回了EAGAIN(errno=11)。EAGAIN不是真正的错误，可以忽略。

fclose有以下几种状态：

RETURN VALUES
If successful, fclose() returns a value of zero. On failure, it returns EOF, and sets errno to one of the following values:
EAGAIN 
The O_NONBLOCK flag is set for the file descriptor underlying stream, and the process would be delayed in the write operation.
EBADF 
The file descriptor underlying stream is not valid.
EFBIG 
The file is a regular file and an attempt was made to write at or beyond the offset maximum associated with the corresponding stream.
EINTR 
The fclose() function was interrupted by a signal.
ENOSPC 
There was no free space remaining on the device containing the file.
EPIPE 
An attempt was made to write to a pipe or FIFO that is not open for reading by any process. A SIGPIPE signal is also sent to the process.