On Wed, 9 Dec 2020 at 21:54, Maxim Levitsky <mlevi...@redhat.com> wrote:
>
> From: Tom Yan <tom.t...@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.t...@gmail.com>
> Signed-off-by: Maxim Levitsky <mlevi...@redhat.com>
> ---
> block/file-posix.c | 59 +++++++++++++++++++++++++++++++++-------------
> 1 file changed, 43 insertions(+), 16 deletions(-)
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index d5fd1dbcd2..226ddbbdad 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.
> + */
The second statement should be removed. Also maybe it's better to have
the first one right above the line `return max_bytes;`.
> +
> #ifdef BLKSECTGET
> int max_bytes = 0;
>
> @@ -1175,7 +1181,22 @@ 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)
> + int sect = 0;
> +
> + if (ioctl(fd, BLKSECTGET, §) == 0) {
> + return sect << 9;
> + } else {
> + return -errno;
> + }
> +#else
> + return -ENOSYS;
> +#endif
> +}
> +
> +static int get_max_segments(int fd)
> {
> #ifdef CONFIG_LINUX
> char buf[32];
> @@ -1230,23 +1251,29 @@ 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)
> @@ -3601,7 +3628,7 @@ 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,
> @@ -3725,7 +3752,7 @@ 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
>
