Hi,
[ Sasha, please remember to CC people who were involved in discussions! ]
On Mon, Apr 18, 2011 at 4:05 PM, Sasha Levin <levinsasha928@xxxxxxxxx> wrote:
> If any of the iov operations return mid-block, use regular ops to complete the current block and continue using iov ops.
>
> Signed-off-by: Sasha Levin <levinsasha928@xxxxxxxxx>
> ---
> tools/kvm/read-write.c | 58 ++++++++++++++++++++++++++++++++++++++++++-----
> 1 files changed, 51 insertions(+), 7 deletions(-)
>
> diff --git a/tools/kvm/read-write.c b/tools/kvm/read-write.c
> index 0c995c8..bf2e4a0 100644
> --- a/tools/kvm/read-write.c
> +++ b/tools/kvm/read-write.c
> @@ -189,10 +189,10 @@ static inline ssize_t get_iov_size(const struct iovec *iov, int iovcnt)
> }
>
> static inline void shift_iovec(const struct iovec **iov, int *iovcnt,
> - size_t nr, ssize_t *total, size_t *count, off_t *offset)
> + ssize_t *nr, ssize_t *total, size_t *count, off_t *offset)
> {
> - while (nr >= (*iov)->iov_len) {
> - nr -= (*iov)->iov_len;
> + while ((size_t)*nr >= (*iov)->iov_len) {
> + *nr -= (*iov)->iov_len;
> *total += (*iov)->iov_len;
> *count -= (*iov)->iov_len;
> if (offset)
> @@ -218,7 +218,18 @@ ssize_t readv_in_full(int fd, const struct iovec *iov, int iovcnt)
> return -1;
> }
>
> - shift_iovec(&iov, &iovcnt, nr, &total, &count, NULL);
> + shift_iovec(&iov, &iovcnt, &nr, &total, &count, NULL);
> +
> + while (nr > 0) {
> + ssize_t nr_readagain;
> + nr_readagain = xread(fd, iov->iov_base + nr,
> + iov->iov_len - nr);
> + if (nr_readagain <= 0)
> + return total;
> +
> + nr += nr_readagain;
> + shift_iovec(&iov, &iovcnt, &nr, &total, &count, NULL);
> + }
> }
>
> return total;
As mentioned on IRC, I hate this patch with a passion. ;-)
We don't do O_DIRECT now so this doesn't help with performance and the
extra complexity it brings to the table isn't very appealing.
Modifying the struct iovec (or making a copy of it) seems to be much
nicer approach.
Pekka
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