[Xen-devel] question about GET_ID_FROM_FREELIST function in blkfront

["Lily Huang" <ushuanglily@xxxxxxxxx>]

Hi,

I noticed that the last element of freelist is initialized to be 0x0fffffff with the code below
---info->shadow[BLK_RING_SIZE-1].req.id = 0x0fffffff;

This means the last element points to an invalid slot. 

But question is: if the last element is allocated, info->shadow_free will be this invalid slot 0x0fffffff, which may trigger the
bug checking code  "BUG_ON(free > BLK_RING_SIZE);" 

How to avoid this? Is this a reasonable design?

Thanks,
-l

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