From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Lei Subject: Re: [PATCH 11/19] block: implement bio helper to add iter bvec pages to bio Date: Thu, 21 Feb 2019 06:58:57 +0800 Message-ID: <20190220225856.GB28313@ming.t460p> References: <20190211190049.7888-1-axboe@kernel.dk> <20190211190049.7888-13-axboe@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190211190049.7888-13-axboe@kernel.dk> Sender: owner-linux-aio@kvack.org To: Jens Axboe Cc: linux-aio@kvack.org, linux-block@vger.kernel.org, linux-api@vger.kernel.org, hch@lst.de, jmoyer@redhat.com, avi@scylladb.com, jannh@google.com, viro@ZenIV.linux.org.uk List-Id: linux-api@vger.kernel.org On Mon, Feb 11, 2019 at 12:00:41PM -0700, Jens Axboe wrote: > For an ITER_BVEC, we can just iterate the iov and add the pages > to the bio directly. This requires that the caller doesn't releases > the pages on IO completion, we add a BIO_NO_PAGE_REF flag for that. > > The current two callers of bio_iov_iter_get_pages() are updated to > check if they need to release pages on completion. This makes them > work with bvecs that contain kernel mapped pages already. > > Reviewed-by: Hannes Reinecke > Reviewed-by: Christoph Hellwig > Signed-off-by: Jens Axboe > --- > block/bio.c | 59 ++++++++++++++++++++++++++++++++------- > fs/block_dev.c | 5 ++-- > fs/iomap.c | 5 ++-- > include/linux/blk_types.h | 1 + > 4 files changed, 56 insertions(+), 14 deletions(-) > > diff --git a/block/bio.c b/block/bio.c > index 4db1008309ed..330df572cfb8 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -828,6 +828,23 @@ int bio_add_page(struct bio *bio, struct page *page, > } > EXPORT_SYMBOL(bio_add_page); > > +static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter) > +{ > + const struct bio_vec *bv = iter->bvec; > + unsigned int len; > + size_t size; > + > + len = min_t(size_t, bv->bv_len, iter->count); > + size = bio_add_page(bio, bv->bv_page, len, > + bv->bv_offset + iter->iov_offset); iter->iov_offset needs to be subtracted from 'len', looks the following delta change[1] is required, otherwise memory corruption can be observed when running xfstests over loop/dio. Another interesting thing is that bio_add_page() is capable of adding multi contiguous pages actually, especially loop uses ITER_BVEC to pass multi-page bvecs. Even though pages in loop's ITER_BVEC may belong to user-space, looks it is still safe to not grab the page ref given it has been done by fs. [1] diff --git a/block/bio.c b/block/bio.c index 3b49963676fc..df99bb3816a1 100644 --- a/block/bio.c +++ b/block/bio.c @@ -842,7 +842,10 @@ static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter) unsigned int len; size_t size; - len = min_t(size_t, bv->bv_len, iter->count); + if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len)) + return -EINVAL; + + len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count); size = bio_add_page(bio, bv->bv_page, len, bv->bv_offset + iter->iov_offset); if (size == len) { Thanks, Ming -- To unsubscribe, send a message with 'unsubscribe linux-aio' in the body to majordomo@kvack.org. For more info on Linux AIO, see: http://www.kvack.org/aio/ Don't email: aart@kvack.org