The read() man page says "The system guarantees to read the number of
bytes requested if the descriptor references a normal file that has
that
many bytes left before the end-of-file, but in no other case." Indeed
with my serial device, if I say to read 15 bytes it sometimes returns
after reading 10 bytes.
Is there anyway to have read() block until the requested length is
ready? Is my only other choice some kind of loop that calls read()
and
usleep() over and over? If so, how do I choose a sleep duration?
Read(2) will block if there is no data so there's no need to sleep.
Using select(2) is one way to go about it but with only one file
descriptor/socket, it seems pointless to me.
unsigned char buffer[15];
size_t len = 0;
int fd = /* something to get your descriptor */
do {
ssize_t ret = read( fd, &buffer[0] + len, sizeof(buffer) - len );
if( ret == -1 )
break;
len += ret;
} while( len < sizeof(buffer) );
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