libceph: new sparse_read op, support sparse reads on msgr2 crc codepath

Add support for a new sparse_read ceph_connection operation. The idea is
that the client driver can define this operation use it to do special
handling for incoming reads.

The alloc_msg routine will look at the request and determine whether the
reply is expected to be sparse. If it is, then we'll dispatch to a
different set of state machine states that will repeatedly call the
driver's sparse_read op to get length and placement info for reading the
extent map, and the extents themselves.

This necessitates adding some new field to some other structs:

- The msg gets a new bool to track whether it's a sparse_read request.

- A new field is added to the cursor to track the amount remaining in the
current extent. This is used to cap the read from the socket into the
msg_data

- Handing a revoke with all of this is particularly difficult, so I've
added a new data_len_remain field to the v2 connection info, and then
use that to skip that much on a revoke. We may want to expand the use of
that to the normal read path as well, just for consistency's sake.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Reviewed-and-tested-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Milind Changire <mchangir@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

include/linux/ceph/messenger.h

@@ -17,6 +17,7 @@
 
 struct ceph_msg;
 struct ceph_connection;
+struct ceph_msg_data_cursor;
 
 /*
  * Ceph defines these callbacks for handling connection events.
@@ -70,6 +71,30 @@ struct ceph_connection_operations {
 				      int used_proto, int result,
 				      const int *allowed_protos, int proto_cnt,
 				      const int *allowed_modes, int mode_cnt);
+
+	/**
+	 * sparse_read: read sparse data
+	 * @con: connection we're reading from
+	 * @cursor: data cursor for reading extents
+	 * @buf: optional buffer to read into
+	 *
+	 * This should be called more than once, each time setting up to
+	 * receive an extent into the current cursor position, and zeroing
+	 * the holes between them.
+	 *
+	 * Returns amount of data to be read (in bytes), 0 if reading is
+	 * complete, or -errno if there was an error.
+	 *
+	 * If @buf is set on a >0 return, then the data should be read into
+	 * the provided buffer. Otherwise, it should be read into the cursor.
+	 *
+	 * The sparse read operation is expected to initialize the cursor
+	 * with a length covering up to the end of the last extent.
+	 */
+	int (*sparse_read)(struct ceph_connection *con,
+			   struct ceph_msg_data_cursor *cursor,
+			   char **buf);
+
 };
 
 /* use format string %s%lld */
@@ -207,6 +232,7 @@ struct ceph_msg_data_cursor {
 
 	struct ceph_msg_data	*data;		/* current data item */
 	size_t			resid;		/* bytes not yet consumed */
+	int			sr_resid;	/* residual sparse_read len */
 	bool			need_crc;	/* crc update needed */
 	union {
 #ifdef CONFIG_BLOCK
@@ -251,6 +277,7 @@ struct ceph_msg {
 	struct kref kref;
 	bool more_to_follow;
 	bool needs_out_seq;
+	bool sparse_read;
 	int front_alloc_len;
 
 	struct ceph_msgpool *pool;
@@ -395,6 +422,7 @@ struct ceph_connection_v2_info {
 
 	void *conn_bufs[16];
 	int conn_buf_cnt;
+	int data_len_remain;
 
 	struct kvec in_sign_kvecs[8];
 	struct kvec out_sign_kvecs[8];

net/ceph/messenger.c

@@ -1013,6 +1013,7 @@ void ceph_msg_data_cursor_init(struct ceph_msg_data_cursor *cursor,
 
 	cursor->total_resid = length;
 	cursor->data = msg->data;
+	cursor->sr_resid = 0;
 
 	__ceph_msg_data_cursor_init(cursor);
 }

net/ceph/messenger_v2.c

@@ -52,14 +52,16 @@
 #define FRAME_LATE_STATUS_COMPLETE	0xe
 #define FRAME_LATE_STATUS_ABORTED_MASK	0xf
 
-#define IN_S_HANDLE_PREAMBLE		1
-#define IN_S_HANDLE_CONTROL		2
-#define IN_S_HANDLE_CONTROL_REMAINDER	3
-#define IN_S_PREPARE_READ_DATA		4
-#define IN_S_PREPARE_READ_DATA_CONT	5
-#define IN_S_PREPARE_READ_ENC_PAGE	6
-#define IN_S_HANDLE_EPILOGUE		7
-#define IN_S_FINISH_SKIP		8
+#define IN_S_HANDLE_PREAMBLE			1
+#define IN_S_HANDLE_CONTROL			2
+#define IN_S_HANDLE_CONTROL_REMAINDER		3
+#define IN_S_PREPARE_READ_DATA			4
+#define IN_S_PREPARE_READ_DATA_CONT		5
+#define IN_S_PREPARE_READ_ENC_PAGE		6
+#define IN_S_PREPARE_SPARSE_DATA		7
+#define IN_S_PREPARE_SPARSE_DATA_CONT		8
+#define IN_S_HANDLE_EPILOGUE			9
+#define IN_S_FINISH_SKIP			10
 
 #define OUT_S_QUEUE_DATA		1
 #define OUT_S_QUEUE_DATA_CONT		2
@@ -1825,6 +1827,123 @@ static void prepare_read_data_cont(struct ceph_connection *con)
 	con->v2.in_state = IN_S_HANDLE_EPILOGUE;
 }
 
+static int prepare_sparse_read_cont(struct ceph_connection *con)
+{
+	int ret;
+	struct bio_vec bv;
+	char *buf = NULL;
+	struct ceph_msg_data_cursor *cursor = &con->v2.in_cursor;
+
+	WARN_ON(con->v2.in_state != IN_S_PREPARE_SPARSE_DATA_CONT);
+
+	if (iov_iter_is_bvec(&con->v2.in_iter)) {
+		if (ceph_test_opt(from_msgr(con->msgr), RXBOUNCE)) {
+			con->in_data_crc = crc32c(con->in_data_crc,
+						  page_address(con->bounce_page),
+						  con->v2.in_bvec.bv_len);
+			get_bvec_at(cursor, &bv);
+			memcpy_to_page(bv.bv_page, bv.bv_offset,
+				       page_address(con->bounce_page),
+				       con->v2.in_bvec.bv_len);
+		} else {
+			con->in_data_crc = ceph_crc32c_page(con->in_data_crc,
+							    con->v2.in_bvec.bv_page,
+							    con->v2.in_bvec.bv_offset,
+							    con->v2.in_bvec.bv_len);
+		}
+
+		ceph_msg_data_advance(cursor, con->v2.in_bvec.bv_len);
+		cursor->sr_resid -= con->v2.in_bvec.bv_len;
+		dout("%s: advance by 0x%x sr_resid 0x%x\n", __func__,
+		     con->v2.in_bvec.bv_len, cursor->sr_resid);
+		WARN_ON_ONCE(cursor->sr_resid > cursor->total_resid);
+		if (cursor->sr_resid) {
+			get_bvec_at(cursor, &bv);
+			if (bv.bv_len > cursor->sr_resid)
+				bv.bv_len = cursor->sr_resid;
+			if (ceph_test_opt(from_msgr(con->msgr), RXBOUNCE)) {
+				bv.bv_page = con->bounce_page;
+				bv.bv_offset = 0;
+			}
+			set_in_bvec(con, &bv);
+			con->v2.data_len_remain -= bv.bv_len;
+			return 0;
+		}
+	} else if (iov_iter_is_kvec(&con->v2.in_iter)) {
+		/* On first call, we have no kvec so don't compute crc */
+		if (con->v2.in_kvec_cnt) {
+			WARN_ON_ONCE(con->v2.in_kvec_cnt > 1);
+			con->in_data_crc = crc32c(con->in_data_crc,
+						  con->v2.in_kvecs[0].iov_base,
+						  con->v2.in_kvecs[0].iov_len);
+		}
+	} else {
+		return -EIO;
+	}
+
+	/* get next extent */
+	ret = con->ops->sparse_read(con, cursor, &buf);
+	if (ret <= 0) {
+		if (ret < 0)
+			return ret;
+
+		reset_in_kvecs(con);
+		add_in_kvec(con, con->v2.in_buf, CEPH_EPILOGUE_PLAIN_LEN);
+		con->v2.in_state = IN_S_HANDLE_EPILOGUE;
+		return 0;
+	}
+
+	if (buf) {
+		/* receive into buffer */
+		reset_in_kvecs(con);
+		add_in_kvec(con, buf, ret);
+		con->v2.data_len_remain -= ret;
+		return 0;
+	}
+
+	if (ret > cursor->total_resid) {
+		pr_warn("%s: ret 0x%x total_resid 0x%zx resid 0x%zx\n",
+			__func__, ret, cursor->total_resid, cursor->resid);
+		return -EIO;
+	}
+	get_bvec_at(cursor, &bv);
+	if (bv.bv_len > cursor->sr_resid)
+		bv.bv_len = cursor->sr_resid;
+	if (ceph_test_opt(from_msgr(con->msgr), RXBOUNCE)) {
+		if (unlikely(!con->bounce_page)) {
+			con->bounce_page = alloc_page(GFP_NOIO);
+			if (!con->bounce_page) {
+				pr_err("failed to allocate bounce page\n");
+				return -ENOMEM;
+			}
+		}
+
+		bv.bv_page = con->bounce_page;
+		bv.bv_offset = 0;
+	}
+	set_in_bvec(con, &bv);
+	con->v2.data_len_remain -= ret;
+	return ret;
+}
+
+static int prepare_sparse_read_data(struct ceph_connection *con)
+{
+	struct ceph_msg *msg = con->in_msg;
+
+	dout("%s: starting sparse read\n", __func__);
+
+	if (WARN_ON_ONCE(!con->ops->sparse_read))
+		return -EOPNOTSUPP;
+
+	if (!con_secure(con))
+		con->in_data_crc = -1;
+
+	reset_in_kvecs(con);
+	con->v2.in_state = IN_S_PREPARE_SPARSE_DATA_CONT;
+	con->v2.data_len_remain = data_len(msg);
+	return prepare_sparse_read_cont(con);
+}
+
 static int prepare_read_tail_plain(struct ceph_connection *con)
 {
 	struct ceph_msg *msg = con->in_msg;
@@ -1845,7 +1964,10 @@ static int prepare_read_tail_plain(struct ceph_connection *con)
 	}
 
 	if (data_len(msg)) {
-		con->v2.in_state = IN_S_PREPARE_READ_DATA;
+		if (msg->sparse_read)
+			con->v2.in_state = IN_S_PREPARE_SPARSE_DATA;
+		else
+			con->v2.in_state = IN_S_PREPARE_READ_DATA;
 	} else {
 		add_in_kvec(con, con->v2.in_buf, CEPH_EPILOGUE_PLAIN_LEN);
 		con->v2.in_state = IN_S_HANDLE_EPILOGUE;
@@ -2898,6 +3020,12 @@ static int populate_in_iter(struct ceph_connection *con)
 			prepare_read_enc_page(con);
 			ret = 0;
 			break;
+		case IN_S_PREPARE_SPARSE_DATA:
+			ret = prepare_sparse_read_data(con);
+			break;
+		case IN_S_PREPARE_SPARSE_DATA_CONT:
+			ret = prepare_sparse_read_cont(con);
+			break;
 		case IN_S_HANDLE_EPILOGUE:
 			ret = handle_epilogue(con);
 			break;
@@ -3489,6 +3617,23 @@ static void revoke_at_prepare_read_enc_page(struct ceph_connection *con)
 	con->v2.in_state = IN_S_FINISH_SKIP;
 }
 
+static void revoke_at_prepare_sparse_data(struct ceph_connection *con)
+{
+	int resid;  /* current piece of data */
+	int remaining;
+
+	WARN_ON(con_secure(con));
+	WARN_ON(!data_len(con->in_msg));
+	WARN_ON(!iov_iter_is_bvec(&con->v2.in_iter));
+	resid = iov_iter_count(&con->v2.in_iter);
+	dout("%s con %p resid %d\n", __func__, con, resid);
+
+	remaining = CEPH_EPILOGUE_PLAIN_LEN + con->v2.data_len_remain;
+	con->v2.in_iter.count -= resid;
+	set_in_skip(con, resid + remaining);
+	con->v2.in_state = IN_S_FINISH_SKIP;
+}
+
 static void revoke_at_handle_epilogue(struct ceph_connection *con)
 {
 	int resid;
@@ -3505,6 +3650,7 @@ static void revoke_at_handle_epilogue(struct ceph_connection *con)
 void ceph_con_v2_revoke_incoming(struct ceph_connection *con)
 {
 	switch (con->v2.in_state) {
+	case IN_S_PREPARE_SPARSE_DATA:
 	case IN_S_PREPARE_READ_DATA:
 		revoke_at_prepare_read_data(con);
 		break;
@@ -3514,6 +3660,9 @@ void ceph_con_v2_revoke_incoming(struct ceph_connection *con)
 	case IN_S_PREPARE_READ_ENC_PAGE:
 		revoke_at_prepare_read_enc_page(con);
 		break;
+	case IN_S_PREPARE_SPARSE_DATA_CONT:
+		revoke_at_prepare_sparse_data(con);
+		break;
 	case IN_S_HANDLE_EPILOGUE:
 		revoke_at_handle_epilogue(con);
 		break;