[PATCH 2/4] erofs-utils: lib: nbd: add support for the netlink reconnection

[Gao Xiang]

In order to support NBD failover.

Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
 lib/backends/nbd.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++
 lib/liberofs_nbd.h |  4 ++
 2 files changed, 97 insertions(+)

diff --git a/lib/backends/nbd.c b/lib/backends/nbd.c
index 7058a81..9b56a56 100644
--- a/lib/backends/nbd.c
+++ b/lib/backends/nbd.c
@@ -174,6 +174,26 @@ err_out:
 	return err;
 }
 
+char *erofs_nbd_get_identifier(int nbdnum)
+{
+	char s[32], *line = NULL;
+	size_t n;
+	FILE *f;
+	int err;
+
+	(void)snprintf(s, sizeof(s), "/sys/block/nbd%d/backend", nbdnum);
+	f = fopen(s, "r");
+	if (!f)
+		return ERR_PTR(-errno);
+
+	if (getline(&line, &n, f) < 0)
+		err = -errno;
+	else
+		err = 0;
+	fclose(f);
+	return err ? ERR_PTR(err) : line;
+}
+
 #if defined(HAVE_NETLINK_GENL_GENL_H) && defined(HAVE_LIBNL_GENL_3)
 enum {
 	NBD_ATTR_UNSPEC,
@@ -209,6 +229,7 @@ enum {
 	NBD_CMD_UNSPEC,
 	NBD_CMD_CONNECT,
 	NBD_CMD_DISCONNECT,
+	NBD_CMD_RECONFIGURE,
 	__NBD_CMD_MAX,
 };
 
@@ -312,6 +333,7 @@ int erofs_nbd_nl_connect(int *index, int blkbits, u64 blocks,
 	NLA_PUT_U64(msg, NBD_ATTR_SIZE_BYTES, blocks << blkbits);
 	NLA_PUT_U64(msg, NBD_ATTR_SERVER_FLAGS, NBD_FLAG_READ_ONLY);
 	NLA_PUT_U64(msg, NBD_ATTR_TIMEOUT, 0);
+	NLA_PUT_U64(msg, NBD_ATTR_DEAD_CONN_TIMEOUT, EROFS_NBD_DEAD_CONN_TIMEOUT);
 	if (identifier)
 		NLA_PUT_STRING(msg, NBD_ATTR_BACKEND_IDENTIFIER, identifier);
 
@@ -339,6 +361,72 @@ int erofs_nbd_nl_connect(int *index, int blkbits, u64 blocks,
 		return cbctx.errcode;
 	return sv[0];
 
+nla_put_failure:
+	nla_nest_cancel(msg, sock_opt);
+	nla_nest_cancel(msg, sock_attr);
+err_nlm_free:
+	nlmsg_free(msg);
+err_nls_free:
+	nl_socket_free(socket);
+err_out:
+	close(sv[0]);
+	close(sv[1]);
+	return err;
+}
+
+int erofs_nbd_nl_reconnect(int index, const char *identifier)
+{
+	struct nlattr *sock_attr, *sock_opt;
+	struct nl_sock *socket;
+	struct nl_msg *msg;
+	int sv[2], err;
+	int driver_id;
+
+	err = socketpair(AF_UNIX, SOCK_STREAM, 0, sv);
+	if (err < 0)
+		return -errno;
+
+	socket = erofs_nbd_get_nl_sock(&driver_id);
+	if (IS_ERR(socket)) {
+		err = PTR_ERR(socket);
+		goto err_out;
+	}
+
+	msg = nlmsg_alloc();
+	if (!msg) {
+		erofs_err("Couldn't allocate netlink message");
+		err = -ENOMEM;
+		goto err_nls_free;
+	}
+
+	genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, driver_id, 0, 0,
+		    NBD_CMD_RECONFIGURE, 0);
+	NLA_PUT_U32(msg, NBD_ATTR_INDEX, index);
+	if (identifier)
+		NLA_PUT_STRING(msg, NBD_ATTR_BACKEND_IDENTIFIER, identifier);
+
+	err = -EINVAL;
+	sock_attr = nla_nest_start(msg, NBD_ATTR_SOCKETS);
+	if (!sock_attr) {
+		erofs_err("Couldn't nest the sockets for our connection");
+		goto err_nlm_free;
+	}
+
+	sock_opt = nla_nest_start(msg, NBD_SOCK_ITEM);
+	if (!sock_attr) {
+		nla_nest_cancel(msg, sock_attr);
+		goto err_nlm_free;
+	}
+	NLA_PUT_U32(msg, NBD_SOCK_FD, sv[1]);
+	nla_nest_end(msg, sock_opt);
+	nla_nest_end(msg, sock_attr);
+
+	err = nl_send_sync(socket, msg);
+	if (err)
+		goto err_out;
+	nl_socket_free(socket);
+	return sv[0];
+
 nla_put_failure:
 	nla_nest_cancel(msg, sock_opt);
 	nla_nest_cancel(msg, sock_attr);
@@ -357,6 +445,11 @@ int erofs_nbd_nl_connect(int *index, int blkbits, u64 blocks,
 {
 	return -EOPNOTSUPP;
 }
+
+int erofs_nbd_nl_reconnect(int index, const char *identifier)
+{
+	return -EOPNOTSUPP;
+}
 #endif
 
 int erofs_nbd_do_it(int nbdfd)
diff --git a/lib/liberofs_nbd.h b/lib/liberofs_nbd.h
index 89c4cf2..03886de 100644
--- a/lib/liberofs_nbd.h
+++ b/lib/liberofs_nbd.h
@@ -31,6 +31,9 @@ struct erofs_nbd_request {
         u32 len;
 } __packed;
 
+/* 30-day timeout for NBD recovery */
+#define EROFS_NBD_DEAD_CONN_TIMEOUT	(3600 * 24 * 30)
+
 long erofs_nbd_in_service(int nbdnum);
 int erofs_nbd_devscan(void);
 int erofs_nbd_connect(int nbdfd, int blkbits, u64 blocks);
@@ -41,4 +44,5 @@ int erofs_nbd_disconnect(int nbdfd);
 
 int erofs_nbd_nl_connect(int *index, int blkbits, u64 blocks,
 			 const char *identifier);
+int erofs_nbd_nl_reconnect(int index, const char *identifier);
 #endif
-- 
2.43.5