ceph: send client metadata to MDS

Implement version 2 of CEPH_MSG_CLIENT_SESSION syntax,
which includes additional client metadata to allow
the MDS to report on clients by user-sensible names
like hostname.

Signed-off-by: John Spray <[e-mail]>
Reviewed-by: Yan, Zheng <[e-mail]>

fs/ceph/mds_client.c

···
 #include <linux/sched.h>
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
+#include <linux/utsname.h>
 
 #include "super.h"
 #include "mds_client.h"
···
 	h = msg->front.iov_base;
 	h->op = cpu_to_le32(op);
 	h->seq = cpu_to_le64(seq);
+
+	return msg;
+}
+
+/*
+ * session message, specialization for CEPH_SESSION_REQUEST_OPEN
+ * to include additional client metadata fields.
+ */
+static struct ceph_msg *create_session_open_msg(struct ceph_mds_client *mdsc, u64 seq)
+{
+	struct ceph_msg *msg;
+	struct ceph_mds_session_head *h;
+	int i = -1;
+	int metadata_bytes = 0;
+	int metadata_key_count = 0;
+	struct ceph_options *opt = mdsc->fsc->client->options;
+	void *p;
+
+	const char* metadata[3][2] = {
+		{"hostname", utsname()->nodename},
+		{"entity_id", opt->name ? opt->name : ""},
+		{NULL, NULL}
+	};
+
+	/* Calculate serialized length of metadata */
+	metadata_bytes = 4;  /* map length */
+	for (i = 0; metadata[i][0] != NULL; ++i) {
+		metadata_bytes += 8 + strlen(metadata[i][0]) +
+			strlen(metadata[i][1]);
+		metadata_key_count++;
+	}
+
+	/* Allocate the message */
+	msg = ceph_msg_new(CEPH_MSG_CLIENT_SESSION, sizeof(*h) + metadata_bytes,
+			   GFP_NOFS, false);
+	if (!msg) {
+		pr_err("create_session_msg ENOMEM creating msg\n");
+		return NULL;
+	}
+	h = msg->front.iov_base;
+	h->op = cpu_to_le32(CEPH_SESSION_REQUEST_OPEN);
+	h->seq = cpu_to_le64(seq);
+
+	/*
+	 * Serialize client metadata into waiting buffer space, using
+	 * the format that userspace expects for map<string, string>
+	 */
+	msg->hdr.version = 2;  /* ClientSession messages with metadata are v2 */
+
+	/* The write pointer, following the session_head structure */
+	p = msg->front.iov_base + sizeof(*h);
+
+	/* Number of entries in the map */
+	ceph_encode_32(&p, metadata_key_count);
+
+	/* Two length-prefixed strings for each entry in the map */
+	for (i = 0; metadata[i][0] != NULL; ++i) {
+		size_t const key_len = strlen(metadata[i][0]);
+		size_t const val_len = strlen(metadata[i][1]);
+
+		ceph_encode_32(&p, key_len);
+		memcpy(p, metadata[i][0], key_len);
+		p += key_len;
+		ceph_encode_32(&p, val_len);
+		memcpy(p, metadata[i][1], val_len);
+		p += val_len;
+	}
+
 	return msg;
 }
 
···
 	session->s_renew_requested = jiffies;
 
 	/* send connect message */
-	msg = create_session_msg(CEPH_SESSION_REQUEST_OPEN, session->s_seq);
+	msg = create_session_open_msg(mdsc, session->s_seq);
 	if (!msg)
 		return -ENOMEM;
 	ceph_con_send(&session->s_con, msg);