Re: [PATCH v3 07/49] bcache: comment on direct access to bvec table
From: Christoph Hellwig <hch@infradead.org>
Date: 2017-08-10 11:26:03
Also in:
linux-block, linux-fsdevel, linux-mm, lkml
I think all this bcache code needs bigger attention. For one bio_alloc_pages is only used in bcache, so we should move it in there. Second the way bio_alloc_pages is currently written looks potentially dangerous for multi-page biovecs, so we should think about a better calling convention. The way bcache seems to generally use it is by allocating a bio, then calling bch_bio_map on it and then calling bio_alloc_pages. I think it just needs a new bio_alloc_pages calling convention that passes the size to be allocated and stop looking into the segment count. Second bch_bio_map isn't something we should be doing in a driver, it should be rewritten using bio_add_page.
quoted hunk ↗ jump to hunk
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c index 866dcf78ff8e..3da595ae565b 100644 --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c@@ -431,6 +431,7 @@ static void do_btree_node_write(struct btree *b) continue_at(cl, btree_node_write_done, NULL); } else { + /* No harm for multipage bvec since the new is just allocated */ b->bio->bi_vcnt = 0;
This should go away - bio_alloc_pages or it's replacement should not modify bi_vcnt on failure.
+ /* single page bio, safe for multipage bvec */ dc->sb_bio.bi_io_vec[0].bv_page = sb_page;
needs to use bio_add_page.
+ /* single page bio, safe for multipage bvec */ ca->sb_bio.bi_io_vec[0].bv_page = sb_page;
needs to use bio_add_page.