[exim] data-phase efficiency

Hi,

    Running strace against a 4.50 delivery process I see:

read(3, "LH+9sNJ1a1QaLik2kkw0v2Ff7vemK1TR"..., 8192) = 8192
alarm(300)                              = 0
write(6, "CY673bSDcJtW0m0mGk2k2EoTpV+6ad27"..., 8190) = 8190
alarm(0)                                = 300
read(3, "Ttv0rVL/a//3e6bSdJtJ\ntBdE3bxsNJ/"..., 8192) = 8192
alarm(300)                              = 0
write(6, "L9fx7b06sNJhpMNJtLiGztTP4hOI/vhu"..., 8190) = 8190
alarm(0)                                = 300
read(3, "yTiJA8GSDuX5PDgPm1sSB4M6s4D5ssSB"..., 8192) = 8192
alarm(300)                              = 0
write(6, "mMR5AToGQBc3mGQLHkBBLmVYZAbZJ4iP"..., 8190) = 8190
alarm(0)                                = 300

Could a select(or poll) for writability be used instead of
alarm, saving one syscall/cycle?

Cheers,
Jeremy