Regardless what manual pages or POSIX say, the driver implements
read() for section filters in such a way that you get either
a full section, or nothing -- provided that the buffer you pass
to read() is large enough for the section (else you will get
partial sections, but never the end of one section and the start
of the next section in one read).
Sorry, I think after a partitial section you read the same section
again, since otherwise the "read 3 bytes, determine length, read whole
section"-sheme wouldn't work. And exactly this leeds to EOVERFLOW,
since the buffer fills and fills and no section will ever be removed
from the buffer.