On Fri, 2023-10-13 at 17:03 +0100, David Howells wrote:
> Add a bvec array pointer and an iterator to netfs_io_request for either
> holding a copy of a DIO iterator or a list of all the bits of buffer
> pointed to by a DIO iterator.
>
> There are two problems: Firstly, if an iovec-class iov_iter is passed to
> ->read_iter() or ->write_iter(), this cannot be passed directly to
> kernel_sendmsg() or kernel_recvmsg() as that may cause locking recursion if
> a fault is generated, so we need to keep track of the pages involved
> separately.
>
> Secondly, if the I/O is asynchronous, we must copy the iov_iter describing
> the buffer before returning to the caller as it may be immediately
> deallocated.
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Jeff Layton <jlayton@xxxxxxxxxx>
> cc: linux-cachefs@xxxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx
> cc: linux-mm@xxxxxxxxx
> ---
> fs/netfs/objects.c | 10 ++++++++++
> include/linux/netfs.h | 3 +++
> 2 files changed, 13 insertions(+)
>
> diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
> index 8e92b8401aaa..4396318081bf 100644
> --- a/fs/netfs/objects.c
> +++ b/fs/netfs/objects.c
> @@ -78,6 +78,7 @@ static void netfs_free_request(struct work_struct *work)
> {
> struct netfs_io_request *rreq =
> container_of(work, struct netfs_io_request, work);
> + unsigned int i;
>
> trace_netfs_rreq(rreq, netfs_rreq_trace_free);
> netfs_proc_del_rreq(rreq);
> @@ -86,6 +87,15 @@ static void netfs_free_request(struct work_struct *work)
> rreq->netfs_ops->free_request(rreq);
> if (rreq->cache_resources.ops)
> rreq->cache_resources.ops->end_operation(&rreq->cache_resources);
> + if (rreq->direct_bv) {
> + for (i = 0; i < rreq->direct_bv_count; i++) {
> + if (rreq->direct_bv[i].bv_page) {
> + if (rreq->direct_bv_unpin)
> + unpin_user_page(rreq->direct_bv[i].bv_page);
> + }
> + }
> + kvfree(rreq->direct_bv);
> + }
> kfree_rcu(rreq, rcu);
> netfs_stat_d(&netfs_n_rh_rreq);
> }
> diff --git a/include/linux/netfs.h b/include/linux/netfs.h
> index bd0437088f0e..66479a61ad00 100644
> --- a/include/linux/netfs.h
> +++ b/include/linux/netfs.h
> @@ -191,7 +191,9 @@ struct netfs_io_request {
> struct list_head subrequests; /* Contributory I/O operations */
> struct iov_iter iter; /* Unencrypted-side iterator */
> struct iov_iter io_iter; /* I/O (Encrypted-side) iterator */
> + struct bio_vec *direct_bv; /* DIO buffer list (when handling iovec-iter) */
> void *netfs_priv; /* Private data for the netfs */
> + unsigned int direct_bv_count; /* Number of elements in bv[] */
nit: "number of elements in direct_bv[]"
Also, just for better readability, can you swap direct_bv and
netfs_priv? Then at least the array and count are together.
> unsigned int debug_id;
> unsigned int rsize; /* Maximum read size (0 for none) */
> atomic_t nr_outstanding; /* Number of ops in progress */
> @@ -200,6 +202,7 @@ struct netfs_io_request {
> size_t len; /* Length of the request */
> short error; /* 0 or error that occurred */
> enum netfs_io_origin origin; /* Origin of the request */
> + bool direct_bv_unpin; /* T if direct_bv[] must be unpinned */
> loff_t i_size; /* Size of the file */
> loff_t start; /* Start position */
> pgoff_t no_unlock_folio; /* Don't unlock this folio after read */
>
--
Jeff Layton <jlayton@xxxxxxxxxx>
