Re: [Qemu-devel] [RFC 01/12] Add iov_writev to use writev to send iovec (also for files)

[Paolo Bonzini <pbonzini@redhat.com>]

Il 21/03/2013 10:09, Orit Wasserman ha scritto:
> We use writev because sendmsg can only be used on socket fds.
> 
> Signed-off-by: Orit Wasserman <owasserm@redhat.com>
> ---
>  include/qemu/iov.h | 12 ++++++++++++
>  util/iov.c         | 36 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/include/qemu/iov.h b/include/qemu/iov.h
> index 68d25f2..e26b7ba 100644
> --- a/include/qemu/iov.h
> +++ b/include/qemu/iov.h
> @@ -82,6 +82,18 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
>  #define iov_send(sockfd, iov, iov_cnt, offset, bytes) \
>    iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, true)
>  
> +/*
> + * writes iovcnt buffers of data described by iov to the file associated with
> + * the file descriptor fd.
> + *
> + * @fd - file descriptor
> + * @iov - iov to write
> + * @invcnt - number of buffers to write
> + *
> + * @return - number of bytes return or -1 on error
> + */
> +ssize_t iov_writev(int fd, struct iovec *iov, unsigned iov_cnt);
> +
>  /**
>   * Produce a text hexdump of iovec `iov' with `iov_cnt' number of elements
>   * in file `fp', prefixing each line with `prefix' and processing not more
> diff --git a/util/iov.c b/util/iov.c
> index 9dae318..bcd6e97 100644
> --- a/util/iov.c
> +++ b/util/iov.c
> @@ -197,6 +197,42 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
>      return ret;
>  }
>  
> +ssize_t iov_writev(int fd, struct iovec *iov, unsigned iov_cnt)
> +{
> +#if defined CONFIG_IOVEC && defined CONFIG_POSIX
> +    ssize_t ret;
> +
> +    do {
> +        ret = writev(fd, iov, iov_cnt);
> +    } while (ret < 0 && errno == EINTR);
> +
> +    return ret;
> +#else
> +    /* else send piece-by-piece */
> +    /*XXX Note: windows has WSASend() and WSARecv() */
> +    unsigned i = 0;
> +    ssize_t ret = 0;
> +    while (i < iov_cnt) {
> +        ssize_t r = send(fd, iov[i].iov_base, iov[i].iov_len, 0);
> +        if (r > 0) {
> +            ret += r;
> +        } else if (!r) {
> +            break;
> +        } else if (errno == EINTR) {
> +            continue;
> +        } else {
> +            /* else it is some "other" error,
> +             * only return if there was no data processed. */
> +            if (ret == 0) {
> +                ret = -1;
> +            }
> +            break;
> +        }
> +        i++;
> +    }
> +    return ret;
> +#endif
> +}

I think this code instead belongs in QEMUFile.  qemu_fflush can use
either a single f->ops->writev_buffer call, or multiple
f->ops->put_buffer calls.

Paolo

>  void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
>                   FILE *fp, const char *prefix, size_t limit)
>