netfs, 9p: Implement helpers for new write code

Implement the helpers for the new write code in 9p.  There's now an
optional ->prepare_write() that allows the filesystem to set the parameters
for the next write, such as maximum size and maximum segment count, and an
->issue_write() that is called to initiate an (asynchronous) write
operation.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Eric Van Hensbergen <ericvh@kernel.org>
cc: Latchesar Ionkov <lucho@ionkov.net>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Christian Schoenebeck <linux_oss@crudebyte.com>
cc: v9fs@lists.linux.dev
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org

2 files changed, 50 insertions, 0 deletions

diff --git a/net/9p/Kconfig b/net/9p/Kconfig
index 00ebce9e5a65..bcdab9c23b40 100644
--- a/net/9p/Kconfig
+++ b/net/9p/Kconfig
@@ -5,6 +5,7 @@
 
 menuconfig NET_9P
 	tristate "Plan 9 Resource Sharing Support (9P2000)"
+	select NETFS_SUPPORT
 	help
 	  If you say Y here, you will get experimental support for
 	  Plan 9 resource sharing via the 9P2000 protocol.
diff --git a/net/9p/client.c b/net/9p/client.c
index f7e90b4769bb..00774656eeac 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -18,6 +18,7 @@
 #include <linux/sched/signal.h>
 #include <linux/uaccess.h>
 #include <linux/uio.h>
+#include <linux/netfs.h>
 #include <net/9p/9p.h>
 #include <linux/parser.h>
 #include <linux/seq_file.h>
@@ -1661,6 +1662,54 @@ p9_client_write(struct p9_fid *fid, u64 offset, struct iov_iter *from, int *err)
 }
 EXPORT_SYMBOL(p9_client_write);
 
+void
+p9_client_write_subreq(struct netfs_io_subrequest *subreq)
+{
+	struct netfs_io_request *wreq = subreq->rreq;
+	struct p9_fid *fid = wreq->netfs_priv;
+	struct p9_client *clnt = fid->clnt;
+	struct p9_req_t *req;
+	unsigned long long start = subreq->start + subreq->transferred;
+	int written, len = subreq->len - subreq->transferred;
+	int err;
+
+	p9_debug(P9_DEBUG_9P, ">>> TWRITE fid %d offset %llu len %d\n",
+		 fid->fid, start, len);
+
+	/* Don't bother zerocopy for small IO (< 1024) */
+	if (clnt->trans_mod->zc_request && len > 1024) {
+		req = p9_client_zc_rpc(clnt, P9_TWRITE, NULL, &subreq->io_iter,
+				       0, wreq->len, P9_ZC_HDR_SZ, "dqd",
+				       fid->fid, start, len);
+	} else {
+		req = p9_client_rpc(clnt, P9_TWRITE, "dqV", fid->fid,
+				    start, len, &subreq->io_iter);
+	}
+	if (IS_ERR(req)) {
+		netfs_write_subrequest_terminated(subreq, PTR_ERR(req), false);
+		return;
+	}
+
+	err = p9pdu_readf(&req->rc, clnt->proto_version, "d", &written);
+	if (err) {
+		trace_9p_protocol_dump(clnt, &req->rc);
+		p9_req_put(clnt, req);
+		netfs_write_subrequest_terminated(subreq, err, false);
+		return;
+	}
+
+	if (written > len) {
+		pr_err("bogus RWRITE count (%d > %u)\n", written, len);
+		written = len;
+	}
+
+	p9_debug(P9_DEBUG_9P, "<<< RWRITE count %d\n", len);
+
+	p9_req_put(clnt, req);
+	netfs_write_subrequest_terminated(subreq, written, false);
+}
+EXPORT_SYMBOL(p9_client_write_subreq);
+
 struct p9_wstat *p9_client_stat(struct p9_fid *fid)
 {
 	int err;