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Re: [Qemu-block] [PATCH v2 14/17] block: Switch transfer length bounds t


From: Kevin Wolf
Subject: Re: [Qemu-block] [PATCH v2 14/17] block: Switch transfer length bounds to byte-based
Date: Tue, 21 Jun 2016 15:50:15 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 14.06.2016 um 23:30 hat Eric Blake geschrieben:
> Sector-based limits are awkward to think about; in our on-going
> quest to move to byte-based interfaces, convert max_transfer_length
> and opt_transfer_length.  Rename them (dropping the _length suffix)
> so that the compiler will help us catch the change in semantics
> across any rebased code, and improve the documentation.  Use unsigned
> values, so that we don't have to worry about negative values and
> so that bit-twiddling is easier; however, we are still constrained
> by 2^31 of signed int in most APIs.
> 
> Signed-off-by: Eric Blake <address@hidden>

> @@ -1738,8 +1742,8 @@ static void iscsi_refresh_limits(BlockDriverState *bs, 
> Error **errp)
>      } else {
>          bs->bl.pwrite_zeroes_alignment = iscsilun->block_size;
>      }
> -    bs->bl.opt_transfer_length =
> -        sector_limits_lun2qemu(iscsilun->bl.opt_xfer_len, iscsilun);
> +    assert(iscsilun->bl.opt_xfer_len < INT_MAX / iscsilun->block_size);
> +    bs->bl.opt_transfer = iscsilun->bl.opt_xfer_len * iscsilun->block_size;
>  }

iscsilun->bl.opt_xfer_len comes directly from libiscsi, and presumably
from the iscsi server, without being checked or sanitised. I don't think
we can assert a specific range of values for it but must assume that it
can be any uint32_t.

We can return an error for a device with a value that we don't like
(even though using the maximum might be just fine), but crashing qemu is
not an option.

> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index aacf132..f2bea85 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -752,7 +752,8 @@ static void raw_refresh_limits(BlockDriverState *bs, 
> Error **errp)
>          if (S_ISBLK(st.st_mode)) {
>              int ret = hdev_get_max_transfer_length(s->fd);
>              if (ret >= 0) {
> -                bs->bl.max_transfer_length = ret;
> +                assert(ret <= BDRV_REQUEST_MAX_SECTORS);
> +                bs->bl.max_transfer = ret << BDRV_SECTOR_BITS;
>              }
>          }
>      }

Same thing here.

Kevin



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