Re: [PATCH 1/2 V2] kvm tools: Add scatter-gather variants of IO functions

[Avi Kivity <avi@redhat.com>]

On 04/16/2011 09:40 PM, Konstantin Khlebnikov wrote:
>
> It might be better to add an helper function, something like this:
>
> static inline void shift_iovec(const struct iovec **iov, int *iovcnt,
>                    size_t nr, ssize_t *total, off_t *offset)
> {
>     while (nr >= (*iov)->iov_len) {
>         nr -= (*iov)->iov_len;
>         *total += (*iov)->iov_len;
>         *offset += (*iov)->iov_len;
>         *iovcnt--;
>         *iov++;
>     }
> }
>

What if nr is nonzero when the loop terminates?  You need to update the 
first iovec entry so you don't redo that segment.

> ssize_t pwritev_in_full(int fd, const struct iovec *iov, int iovcnt, 
> off_t offset)
> {
>     ssize_t nr, total = 0;
>
>     while (iovcnt) {
>         nr = xpwritev(fd, iov, iovcnt, offset);
>         if (nr < 0)
>             return -1;
>         if (nr == 0) {
>             errno = ENOSPC;
>             return -1;
>         }
>         shift_iovec(&iov, &iovcnt, nr, &total, &offset);
>     }
>
>     return total;
> }
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-- 
error compiling committee.c: too many arguments to function