afs: Set up the iov_iter before calling afs_extract_data()

afs_extract_data() sets up a temporary iov_iter and passes it to AF_RXRPC
each time it is called to describe the remaining buffer to be filled.

Instead:

 (1) Put an iterator in the afs_call struct.

 (2) Set the iterator for each marshalling stage to load data into the
     appropriate places.  A number of convenience functions are provided to
     this end (eg. afs_extract_to_buf()).

     This iterator is then passed to afs_extract_data().

 (3) Use the new ITER_XARRAY iterator when reading data to load directly
     into the inode's pages without needing to create a list of them.

This will allow O_DIRECT calls to be supported in future patches.

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-By: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/152898380012.11616.12094591785228251717.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/153685394431.14766.3178466345696987059.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/153999787395.866.11218209749223643998.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/154033911195.12041.3882700371848894587.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/158861250059.340223.1248231474865140653.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/159465827399.1377938.11181327349704960046.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/160588533776.3465195.3612752083351956948.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161118151238.1232039.17015723405750601161.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/161161047240.2537118.14721975104810564022.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161340410333.1303470.16260122230371140878.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/161539554187.286939.15305559004905459852.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/161653810525.2770958.4630666029125411789.stgit@warthog.procyon.org.uk/ # v5
Link: https://lore.kernel.org/r/161789093719.6155.7877160739235087723.stgit@warthog.procyon.org.uk/ # v6

1 files changed, 14 insertions, 40 deletions

diff --git a/fs/afs/yfsclient.c b/fs/afs/yfsclient.c
index 6c45d32da13c..abcec145db4b 100644
--- a/fs/afs/yfsclient.c
+++ b/fs/afs/yfsclient.c
@@ -360,7 +360,6 @@ static int yfs_deliver_fs_fetch_data64(struct afs_call *call)
 	struct afs_vnode_param *vp = &op->file[0];
 	struct afs_read *req = op->fetch.req;
 	const __be32 *bp;
-	unsigned int size;
 	int ret;
 
 	_enter("{%u,%zu, %zu/%llu}",
@@ -370,13 +369,14 @@ static int yfs_deliver_fs_fetch_data64(struct afs_call *call)
 	switch (call->unmarshall) {
 	case 0:
 		req->actual_len = 0;
-		req->index = 0;
-		req->offset = req->pos & (PAGE_SIZE - 1);
 		afs_extract_to_tmp64(call);
 		call->unmarshall++;
 		fallthrough;
 
-		/* extract the returned data length */
+		/* Extract the returned data length into ->actual_len.  This
+		 * may indicate more or less data than was requested will be
+		 * returned.
+		 */
 	case 1:
 		_debug("extract data length");
 		ret = afs_extract_data(call, true);
@@ -385,45 +385,25 @@ static int yfs_deliver_fs_fetch_data64(struct afs_call *call)
 
 		req->actual_len = be64_to_cpu(call->tmp64);
 		_debug("DATA length: %llu", req->actual_len);
-		req->remain = min(req->len, req->actual_len);
-		if (req->remain == 0)
+
+		if (req->actual_len == 0)
 			goto no_more_data;
 
+		call->iter = req->iter;
+		call->iov_len = min(req->actual_len, req->len);
 		call->unmarshall++;
-
-	begin_page:
-		ASSERTCMP(req->index, <, req->nr_pages);
-		if (req->remain > PAGE_SIZE - req->offset)
-			size = PAGE_SIZE - req->offset;
-		else
-			size = req->remain;
-		call->iov_len = size;
-		call->bvec[0].bv_len = size;
-		call->bvec[0].bv_offset = req->offset;
-		call->bvec[0].bv_page = req->pages[req->index];
-		iov_iter_bvec(&call->def_iter, READ, call->bvec, 1, size);
-		ASSERTCMP(size, <=, PAGE_SIZE);
 		fallthrough;
 
 		/* extract the returned data */
 	case 2:
 		_debug("extract data %zu/%llu",
-		       iov_iter_count(call->iter), req->remain);
+		       iov_iter_count(call->iter), req->actual_len);
 
 		ret = afs_extract_data(call, true);
 		if (ret < 0)
 			return ret;
-		req->remain -= call->bvec[0].bv_len;
-		req->offset += call->bvec[0].bv_len;
-		ASSERTCMP(req->offset, <=, PAGE_SIZE);
-		if (req->offset == PAGE_SIZE) {
-			req->offset = 0;
-			req->index++;
-			if (req->remain > 0)
-				goto begin_page;
-		}
 
-		ASSERTCMP(req->remain, ==, 0);
+		call->iter = &call->def_iter;
 		if (req->actual_len <= req->len)
 			goto no_more_data;
 
@@ -469,16 +449,8 @@ static int yfs_deliver_fs_fetch_data64(struct afs_call *call)
 		break;
 	}
 
-	for (; req->index < req->nr_pages; req->index++) {
-		if (req->offset < PAGE_SIZE)
-			zero_user_segment(req->pages[req->index],
-					  req->offset, PAGE_SIZE);
-		req->offset = 0;
-	}
-
-	if (req->page_done)
-		for (req->index = 0; req->index < req->nr_pages; req->index++)
-			req->page_done(req);
+	if (req->done)
+		req->done(req);
 
 	_leave(" = 0 [done]");
 	return 0;
@@ -518,6 +490,8 @@ void yfs_fs_fetch_data(struct afs_operation *op)
 	if (!call)
 		return afs_op_nomem(op);
 
+	req->call_debug_id = call->debug_id;
+
 	/* marshall the parameters */
 	bp = call->request;
 	bp = xdr_encode_u32(bp, YFSFETCHDATA64);