Re: [PATCH 1/5] file-posix: split hdev_refresh_limits from raw_refresh_limits

[Maxim Levitsky <mlevitsk@redhat.com>]

On Thu, 2020-11-05 at 13:44 +0800, Tom Yan wrote:
> Actually I made a mistake in this. BLKSECTGET (the one in the block
> layer) returns the number of "sectors", which is "defined" as 512-byte
> block. So we shouldn't use BLKSSZGET here, but simply 512 (1 << 9).
> See logical_to_sectors() in sd.h of the kernel.
I see it now. I'll respin the patches in a few days I guess after the rest
of the patches are reviewed.

Best regards,
	Maxim Levitsky

> 
> On Thu, 5 Nov 2020 at 01:32, Maxim Levitsky <mlevitsk@redhat.com> wrote:
> > From: Tom Yan <tom.ty89@gmail.com>
> > 
> > We can and should get max transfer length and max segments for all host
> > devices / cdroms (on Linux).
> > 
> > Also use MIN_NON_ZERO instead when we clamp max transfer length against
> > max segments.
> > 
> > Signed-off-by: Tom Yan <tom.ty89@gmail.com>
> > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > ---
> >  block/file-posix.c | 61 ++++++++++++++++++++++++++++++++++------------
> >  1 file changed, 45 insertions(+), 16 deletions(-)
> > 
> > diff --git a/block/file-posix.c b/block/file-posix.c
> > index c63926d592..6581f41b2b 100644
> > --- a/block/file-posix.c
> > +++ b/block/file-posix.c
> > @@ -1162,6 +1162,12 @@ static void raw_reopen_abort(BDRVReopenState *state)
> > 
> >  static int sg_get_max_transfer_length(int fd)
> >  {
> > +    /*
> > +     * BLKSECTGET for /dev/sg* character devices incorrectly returns
> > +     * the max transfer size in bytes (rather than in blocks).
> > +     * Also note that /dev/sg* doesn't support BLKSSZGET ioctl.
> > +     */
> > +
> >  #ifdef BLKSECTGET
> >      int max_bytes = 0;
> > 
> > @@ -1175,7 +1181,24 @@ static int sg_get_max_transfer_length(int fd)
> >  #endif
> >  }
> > 
> > -static int sg_get_max_segments(int fd)
> > +static int get_max_transfer_length(int fd)
> > +{
> > +#if defined(BLKSECTGET) && defined(BLKSSZGET)
> > +    int sect = 0;
> > +    int ssz = 0;
> > +
> > +    if (ioctl(fd, BLKSECTGET, &sect) == 0 &&
> > +        ioctl(fd, BLKSSZGET, &ssz) == 0) {
> > +        return sect * ssz;
> > +    } else {
> > +        return -errno;
> > +    }
> > +#else
> > +    return -ENOSYS;
> > +#endif
> > +}
> > +
> > +static int get_max_segments(int fd)
> >  {
> >  #ifdef CONFIG_LINUX
> >      char buf[32];
> > @@ -1230,23 +1253,29 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
> >  {
> >      BDRVRawState *s = bs->opaque;
> > 
> > -    if (bs->sg) {
> > -        int ret = sg_get_max_transfer_length(s->fd);
> > +    raw_probe_alignment(bs, s->fd, errp);
> > +    bs->bl.min_mem_alignment = s->buf_align;
> > +    bs->bl.opt_mem_alignment = MAX(s->buf_align, qemu_real_host_page_size);
> > +}
> > 
> > -        if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
> > -            bs->bl.max_transfer = pow2floor(ret);
> > -        }
> > +static void hdev_refresh_limits(BlockDriverState *bs, Error **errp)
> > +{
> > +    BDRVRawState *s = bs->opaque;
> > 
> > -        ret = sg_get_max_segments(s->fd);
> > -        if (ret > 0) {
> > -            bs->bl.max_transfer = MIN(bs->bl.max_transfer,
> > -                                      ret * qemu_real_host_page_size);
> > -        }
> > +    int ret = bs->sg ? sg_get_max_transfer_length(s->fd) :
> > +                       get_max_transfer_length(s->fd);
> > +
> > +    if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
> > +        bs->bl.max_transfer = pow2floor(ret);
> >      }
> > 
> > -    raw_probe_alignment(bs, s->fd, errp);
> > -    bs->bl.min_mem_alignment = s->buf_align;
> > -    bs->bl.opt_mem_alignment = MAX(s->buf_align, qemu_real_host_page_size);
> > +    ret = get_max_segments(s->fd);
> > +    if (ret > 0) {
> > +        bs->bl.max_transfer = MIN_NON_ZERO(bs->bl.max_transfer,
> > +                                           ret * qemu_real_host_page_size);
> > +    }
> > +
> > +    raw_refresh_limits(bs, errp);
> >  }
> > 
> >  static int check_for_dasd(int fd)
> > @@ -3600,7 +3629,7 @@ static BlockDriver bdrv_host_device = {
> >      .bdrv_co_pdiscard       = hdev_co_pdiscard,
> >      .bdrv_co_copy_range_from = raw_co_copy_range_from,
> >      .bdrv_co_copy_range_to  = raw_co_copy_range_to,
> > -    .bdrv_refresh_limits = raw_refresh_limits,
> > +    .bdrv_refresh_limits = hdev_refresh_limits,
> >      .bdrv_io_plug = raw_aio_plug,
> >      .bdrv_io_unplug = raw_aio_unplug,
> >      .bdrv_attach_aio_context = raw_aio_attach_aio_context,
> > @@ -3724,7 +3753,7 @@ static BlockDriver bdrv_host_cdrom = {
> >      .bdrv_co_preadv         = raw_co_preadv,
> >      .bdrv_co_pwritev        = raw_co_pwritev,
> >      .bdrv_co_flush_to_disk  = raw_co_flush_to_disk,
> > -    .bdrv_refresh_limits = raw_refresh_limits,
> > +    .bdrv_refresh_limits = hdev_refresh_limits,
> >      .bdrv_io_plug = raw_aio_plug,
> >      .bdrv_io_unplug = raw_aio_unplug,
> >      .bdrv_attach_aio_context = raw_aio_attach_aio_context,
> > --
> > 2.26.2
> >