On 01/13/2015 04:36 PM, Richard Weinberger wrote: > > > Am 14.01.2015 um 00:30 schrieb Jens Axboe: >>> If I understand you correctly it can happen that blk_rq_bytes() returns >>> more bytes than blk_rq_map_sg() allocated, right? >> >> No, the number of bytes will be the same, no magic is involved :-) > > Good to know. :) > >> But lets say the initial request has 4 bios, with each 2 pages, for a >> total of 8 segments. Lets further assume that the pages in each bio are >> contiguous, so that blk_rq_map_sg() will map this to 4 sg elements, each >> 2xpages long. >> >> Now, this may already be handled just fine, and you don't need to >> update/store the actual sg count. I just looked at the source, and I'm >> assuming it'll do the right thing (ubi_read_sg() will bump the active sg >> element, when that size has been consumed), but I don't have >> ubi_read_sg() in my tree to verify. > > Currently the sg count is hard coded to UBI_MAX_SG_COUNT.
The max count doesn't matter, that just provides you a guarantee that you'll never receive a request that maps to more than that. The point I'm trying to make is that if you receive 8 segments and it maps to 4, then you better not look at segments 5..8 after it being mapped. Whatever the max is, doesn't matter in this conversation. > I'm sorry, I forgot to CC you and hch to this patch: Which is as I suspected, you'll do each segment to the length specified, hence you don't need to track the returned count from blk_rq_map_sg(). -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
