libceph: add new iov_iter-based ceph_msg_data_type and ceph_osd_data_type

Add an iov_iter to the unions in ceph_msg_data and ceph_msg_data_cursor.
Instead of requiring a list of pages or bvecs, we can just use an
iov_iter directly, and avoid extra allocations.

We assume that the pages represented by the iter are pinned such that
they shouldn't incur page faults, which is the case for the iov_iters
created by netfs.

While working on this, Al Viro informed me that he was going to change
iov_iter_get_pages to auto-advance the iterator as that pattern is more
or less required for ITER_PIPE anyway. We emulate that here for now by
advancing in the _next op and tracking that amount in the "lastlen"
field.

In the event that _next is called twice without an intervening
_advance, we revert the iov_iter by the remaining lastlen before
calling iov_iter_get_pages.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Reviewed-and-tested-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Milind Changire <mchangir@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/ceph/messenger.h b/include/linux/ceph/messenger.h
index 9fd7255172ad..2eaaabbe98cb 100644
--- a/include/linux/ceph/messenger.h
+++ b/include/linux/ceph/messenger.h
@@ -123,6 +123,7 @@ enum ceph_msg_data_type {
 	CEPH_MSG_DATA_BIO,	/* data source/destination is a bio list */
 #endif /* CONFIG_BLOCK */
 	CEPH_MSG_DATA_BVECS,	/* data source/destination is a bio_vec array */
+	CEPH_MSG_DATA_ITER,	/* data source/destination is an iov_iter */
 };
 
 #ifdef CONFIG_BLOCK
@@ -224,6 +225,7 @@ struct ceph_msg_data {
 			bool		own_pages;
 		};
 		struct ceph_pagelist	*pagelist;
+		struct iov_iter		iter;
 	};
 };
 
@@ -248,6 +250,10 @@ struct ceph_msg_data_cursor {
 			struct page	*page;		/* page from list */
 			size_t		offset;		/* bytes from list */
 		};
+		struct {
+			struct iov_iter		iov_iter;
+			unsigned int		lastlen;
+		};
 	};
 };
 
@@ -605,6 +611,8 @@ void ceph_msg_data_add_bio(struct ceph_msg *msg, struct ceph_bio_iter *bio_pos,
 #endif /* CONFIG_BLOCK */
 void ceph_msg_data_add_bvecs(struct ceph_msg *msg,
 			     struct ceph_bvec_iter *bvec_pos);
+void ceph_msg_data_add_iter(struct ceph_msg *msg,
+			    struct iov_iter *iter);
 
 struct ceph_msg *ceph_msg_new2(int type, int front_len, int max_data_items,
 			       gfp_t flags, bool can_fail);