Techniques for handling short reads/writes with scatter-gather?

Question

Scatter-gather - readv()/writev()/preadv()/pwritev() - reads/writes a variable number of iovec structs in a single system call. Basically it reads/write each buffer sequentiall

Answer 1

Use a loop like the following to advance the partially-processed iov:

for (;;) {
    written = writev(fd, iov+cur, count-cur);
    if (written < 0) goto error;
    while (cur < count && written >= iov[cur].iov_len)
        written -= iov[cur++].iov_len;
    if (cur == count) break;
    iov[cur].iov_base = (char *)iov[cur].iov_base + written;
    iov[cur].iov_len -= written;
}

Note that if you don't check for cur < count you will read past the end of iov which might contain zero.