9pnet: allow making incomplete read requests

A user doesn't necessarily want to wait for all the requested data to
be available, since the waiting time for each request is unbounded.

The new method permits sending one read request at a time and getting
the response ASAP, allowing to use 9pnet with synthetic file systems
representing arbitrary data streams.

Link: http://lkml.kernel.org/r/20200205204053.12751-1-l29ah@cock.li
Signed-off-by: Sergey Alirzaev <l29ah@cock.li>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>

1 files changed, 73 insertions, 61 deletions

diff --git a/net/9p/client.c b/net/9p/client.c
index 1d48afc7033c..fc1f3635e5dd 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -1549,82 +1549,94 @@ EXPORT_SYMBOL(p9_client_unlinkat);
 int
 p9_client_read(struct p9_fid *fid, u64 offset, struct iov_iter *to, int *err)
 {
-	struct p9_client *clnt = fid->clnt;
-	struct p9_req_t *req;
 	int total = 0;
 	*err = 0;
 
+	while (iov_iter_count(to)) {
+		int count;
+
+		count = p9_client_read_once(fid, offset, to, err);
+		if (!count || *err)
+			break;
+		offset += count;
+		total += count;
+	}
+	return total;
+}
+EXPORT_SYMBOL(p9_client_read);
+
+int
+p9_client_read_once(struct p9_fid *fid, u64 offset, struct iov_iter *to,
+		    int *err)
+{
+	struct p9_client *clnt = fid->clnt;
+	struct p9_req_t *req;
+	int count = iov_iter_count(to);
+	int rsize, non_zc = 0;
+	char *dataptr;
+
+	*err = 0;
 	p9_debug(P9_DEBUG_9P, ">>> TREAD fid %d offset %llu %d\n",
 		   fid->fid, (unsigned long long) offset, (int)iov_iter_count(to));
 
-	while (iov_iter_count(to)) {
-		int count = iov_iter_count(to);
-		int rsize, non_zc = 0;
-		char *dataptr;
+	rsize = fid->iounit;
+	if (!rsize || rsize > clnt->msize - P9_IOHDRSZ)
+		rsize = clnt->msize - P9_IOHDRSZ;
 
-		rsize = fid->iounit;
-		if (!rsize || rsize > clnt->msize-P9_IOHDRSZ)
-			rsize = clnt->msize - P9_IOHDRSZ;
+	if (count < rsize)
+		rsize = count;
 
-		if (count < rsize)
-			rsize = count;
+	/* Don't bother zerocopy for small IO (< 1024) */
+	if (clnt->trans_mod->zc_request && rsize > 1024) {
+		/* response header len is 11
+		 * PDU Header(7) + IO Size (4)
+		 */
+		req = p9_client_zc_rpc(clnt, P9_TREAD, to, NULL, rsize,
+				       0, 11, "dqd", fid->fid,
+				       offset, rsize);
+	} else {
+		non_zc = 1;
+		req = p9_client_rpc(clnt, P9_TREAD, "dqd", fid->fid, offset,
+				    rsize);
+	}
+	if (IS_ERR(req)) {
+		*err = PTR_ERR(req);
+		return 0;
+	}
 
-		/* Don't bother zerocopy for small IO (< 1024) */
-		if (clnt->trans_mod->zc_request && rsize > 1024) {
-			/*
-			 * response header len is 11
-			 * PDU Header(7) + IO Size (4)
-			 */
-			req = p9_client_zc_rpc(clnt, P9_TREAD, to, NULL, rsize,
-					       0, 11, "dqd", fid->fid,
-					       offset, rsize);
-		} else {
-			non_zc = 1;
-			req = p9_client_rpc(clnt, P9_TREAD, "dqd", fid->fid, offset,
-					    rsize);
-		}
-		if (IS_ERR(req)) {
-			*err = PTR_ERR(req);
-			break;
-		}
+	*err = p9pdu_readf(&req->rc, clnt->proto_version,
+			   "D", &count, &dataptr);
+	if (*err) {
+		trace_9p_protocol_dump(clnt, &req->rc);
+		p9_tag_remove(clnt, req);
+		return 0;
+	}
+	if (rsize < count) {
+		pr_err("bogus RREAD count (%d > %d)\n", count, rsize);
+		count = rsize;
+	}
 
-		*err = p9pdu_readf(&req->rc, clnt->proto_version,
-				   "D", &count, &dataptr);
-		if (*err) {
-			trace_9p_protocol_dump(clnt, &req->rc);
-			p9_tag_remove(clnt, req);
-			break;
-		}
-		if (rsize < count) {
-			pr_err("bogus RREAD count (%d > %d)\n", count, rsize);
-			count = rsize;
-		}
+	p9_debug(P9_DEBUG_9P, "<<< RREAD count %d\n", count);
+	if (!count) {
+		p9_tag_remove(clnt, req);
+		return 0;
+	}
 
-		p9_debug(P9_DEBUG_9P, "<<< RREAD count %d\n", count);
-		if (!count) {
-			p9_tag_remove(clnt, req);
-			break;
-		}
+	if (non_zc) {
+		int n = copy_to_iter(dataptr, count, to);
 
-		if (non_zc) {
-			int n = copy_to_iter(dataptr, count, to);
-			total += n;
-			offset += n;
-			if (n != count) {
-				*err = -EFAULT;
-				p9_tag_remove(clnt, req);
-				break;
-			}
-		} else {
-			iov_iter_advance(to, count);
-			total += count;
-			offset += count;
+		if (n != count) {
+			*err = -EFAULT;
+			p9_tag_remove(clnt, req);
+			return n;
 		}
-		p9_tag_remove(clnt, req);
+	} else {
+		iov_iter_advance(to, count);
 	}
-	return total;
+	p9_tag_remove(clnt, req);
+	return count;
 }
-EXPORT_SYMBOL(p9_client_read);
+EXPORT_SYMBOL(p9_client_read_once);
 
 int
 p9_client_write(struct p9_fid *fid, u64 offset, struct iov_iter *from, int *err)