On Mon, 2018-01-22 at 16:14 -0700, Jens Axboe wrote:
> On 1/22/18 3:25 PM, Elliott, Robert (Persistent Memory) wrote:
> > fio engines/sg.c fio_sgio_rw_doio() has that pattern:
> >
> > ret = write(f->fd, hdr, sizeof(*hdr));
> > if (ret < 0)
> > return ret;
> > ...
> > return FIO_Q_QUEUED; [which is 1]
> >
> > although there might be special circumstances for the sg interface
> > making that safe.
>
> That's for SG scsi direct IO, I don't think that supports partial
> IO since it's sending raw SCSI commands.
>
> For the regular libaio or sync IO system calls, fio of course checks
> and handles short IOs correctly. It even logs if it got any.
The entire fio_sgio_rw_doio() function is as follows:
static int fio_sgio_rw_doio(struct fio_file *f, struct io_u *io_u, int do_sync)
{
struct sg_io_hdr *hdr = &io_u->hdr;
int ret;
ret = write(f->fd, hdr, sizeof(*hdr));
if (ret < 0)
return ret;
if (do_sync) {
ret = read(f->fd, hdr, sizeof(*hdr));
if (ret < 0)
return ret;
/* record if an io error occurred */
if (hdr->info & SG_INFO_CHECK)
io_u->error = EIO;
return FIO_Q_COMPLETED;
}
return FIO_Q_QUEUED;
}
I think the 'resid' member of the struct sg_io_hdr that is provided by the
sg_io kernel driver as a response represents the number of bytes that has not
been written. So it should be possible to recognize and handle short I/Os in
that function. From include/scsi/sg.h:
int resid; /* [o] dxfer_len - actual_transferred */
Bart.
