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403542f910
This patch adds basic tracking of outstanding DMA requests on grant table entries marked as PageForeign. When a PageForeign struct page is about to be mapped for DMA, we set its map count to 1 (or zero in actual value). This is then checked for when we need to free a grant table entry early to ensure that we don't free an entry that's currently used for DMA. So any entry that has been marked for DMA will not be freed early. If the unmapping API had a struct page (which exists for the sg case) then we could do this properly. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>