Re: [PATCH v2 01/16] iscsi-target: add callback to alloc and free PDU

[Varun Prakash <varun@chelsio.com>]

On Sun, Apr 10, 2016 at 08:33:53PM +0300, Sagi Grimberg wrote:
> 
> 
> On 09/04/16 16:11, Varun Prakash wrote:
> >Add two callbacks to struct iscsit_transport -
> >
> >1. void *(*iscsit_alloc_pdu)()
> >    iscsi-target uses this callback for
> >    iSCSI PDU allocation.
> >
> >2. void (*iscsit_free_pdu)
> >    iscsi-target uses this callback
> >    to free an iSCSI PDU which was
> >    allocated by iscsit_alloc_pdu().
> 
> Can you please explain why are you adding two different
> callouts? Who (Chelsio T5) will need it, and why they can't
> use the in-cmd pdu?

I am adding these to avoid per PDU 48 bytes(BHS) memcpy from cmd->pdu to
transport driver tx buffer, iscsi-target can directly form iscsi hdr
in transport driver tx buffer. 

> 
> >
> >Signed-off-by: Varun Prakash <varun@chelsio.com>
> >---
> >  drivers/target/iscsi/iscsi_target.c    | 76 ++++++++++++++++++++++++++++------
> >  include/target/iscsi/iscsi_transport.h |  2 +
> >  2 files changed, 65 insertions(+), 13 deletions(-)
> >
> >diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
> >index 961202f..fdb33ba 100644
> >--- a/drivers/target/iscsi/iscsi_target.c
> >+++ b/drivers/target/iscsi/iscsi_target.c
> >@@ -499,6 +499,11 @@ static void iscsit_aborted_task(struct iscsi_conn *conn, struct iscsi_cmd *cmd)
> >  	__iscsit_free_cmd(cmd, scsi_cmd, true);
> >  }
> >
> >+static void *iscsit_alloc_pdu(struct iscsi_conn *conn, struct iscsi_cmd *cmd)
> >+{
> >+	return cmd->pdu;
> >+}
> >+
> >  static enum target_prot_op iscsit_get_sup_prot_ops(struct iscsi_conn *conn)
> >  {
> >  	return TARGET_PROT_NORMAL;
> >@@ -519,6 +524,7 @@ static struct iscsit_transport iscsi_target_transport = {
> >  	.iscsit_queue_data_in	= iscsit_queue_rsp,
> >  	.iscsit_queue_status	= iscsit_queue_rsp,
> >  	.iscsit_aborted_task	= iscsit_aborted_task,
> >+	.iscsit_alloc_pdu	= iscsit_alloc_pdu,
> >  	.iscsit_get_sup_prot_ops = iscsit_get_sup_prot_ops,
> >  };
> >
> >@@ -2537,7 +2543,10 @@ static int iscsit_send_conn_drop_async_message(
> >  	cmd->tx_size = ISCSI_HDR_LEN;
> >  	cmd->iscsi_opcode = ISCSI_OP_ASYNC_EVENT;
> >
> >-	hdr			= (struct iscsi_async *) cmd->pdu;
> >+	hdr = conn->conn_transport->iscsit_alloc_pdu(conn, cmd);
> >+	if (unlikely(!hdr))
> >+		return -ENOMEM;
> >+
> >  	hdr->opcode		= ISCSI_OP_ASYNC_EVENT;
> >  	hdr->flags		= ISCSI_FLAG_CMD_FINAL;
> >  	cmd->init_task_tag	= RESERVED_ITT;
> >@@ -2630,7 +2639,7 @@ iscsit_build_datain_pdu(struct iscsi_cmd *cmd, struct iscsi_conn *conn,
> >
> >  static int iscsit_send_datain(struct iscsi_cmd *cmd, struct iscsi_conn *conn)
> >  {
> >-	struct iscsi_data_rsp *hdr = (struct iscsi_data_rsp *)&cmd->pdu[0];
> >+	struct iscsi_data_rsp *hdr;
> >  	struct iscsi_datain datain;
> >  	struct iscsi_datain_req *dr;
> >  	struct kvec *iov;
> >@@ -2675,6 +2684,10 @@ static int iscsit_send_datain(struct iscsi_cmd *cmd, struct iscsi_conn *conn)
> >  			set_statsn = true;
> >  	}
> >
> >+	hdr = conn->conn_transport->iscsit_alloc_pdu(conn, cmd);
> >+	if (unlikely(!hdr))
> >+		return -ENOMEM;
> >+
> >  	iscsit_build_datain_pdu(cmd, conn, &datain, hdr, set_statsn);
> >
> >  	iov = &cmd->iov_data[0];
> >@@ -2843,13 +2856,20 @@ EXPORT_SYMBOL(iscsit_build_logout_rsp);
> >  static int
> >  iscsit_send_logout(struct iscsi_cmd *cmd, struct iscsi_conn *conn)
> >  {
> >+	struct iscsi_logout_rsp *hdr;
> >  	struct kvec *iov;
> >  	int niov = 0, tx_size, rc;
> >
> >-	rc = iscsit_build_logout_rsp(cmd, conn,
> >-			(struct iscsi_logout_rsp *)&cmd->pdu[0]);
> >-	if (rc < 0)
> >+	hdr = conn->conn_transport->iscsit_alloc_pdu(conn, cmd);
> >+	if (unlikely(!hdr))
> >+		return -ENOMEM;
> >+
> >+	rc = iscsit_build_logout_rsp(cmd, conn, hdr);
> >+	if (rc < 0) {
> >+		if (conn->conn_transport->iscsit_free_pdu)
> >+			conn->conn_transport->iscsit_free_pdu(conn, cmd);
> 
> This creates a weird asymmetry where alloc is called unconditionally
> while free is conditional, I'd say implement an empty free for iscsit.
> Same for the rest of the code...

Ok, I will add empty pdu free function for iscsi-target.
 
> 
> P.S. I didn't see any non-error path call to free_pdu, is that a
> possible leak (for drivers that actually allocate a PDU)?

In non error path there is a call to xmit_pdu after pdu allocation
so no leak.
  
> 
> On another unrelated note, I'd be very happy if we lose the iscsit_
> prefix from all the callouts, it clear to everyone that it iscsi, no
> need for an explicit reminder...

Ok, I will remove iscsit_ prefix if Nicholas agrees on this.