On 01/27/2010 02:41 AM, Jack Z wrote:
Hi group,
I'm looking at the following code and come up with some questions....
In this function,
static void iscsi_sw_tcp_write_space(struct sock *sk)
{
struct iscsi_conn *conn = (struct iscsi_conn*)sk->sk_user_data;
struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
tcp_sw_conn->old_write_space(sk);
ISCSI_SW_TCP_DBG(conn, "iscsi_write_space\n");
iscsi_conn_queue_work(conn);
}
tcp_sw_conn->old_write_space() is called. And in the following
function, tcp_sw_conn->old_write_space() seems to be assigned to the
original value of "sk->sk_write_space"...
Could anyone show me which function does "sk->sk_write_space" point to
before it is assigned to "iscsi_sw_tcp_write_space;" later in the same
function?
I believe it is sk_stream_write_space. For tcp v4 sockets see
tcp_v4_init_sock.
static void iscsi_sw_tcp_conn_set_callbacks(struct iscsi_conn *conn)
{
struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
struct sock *sk = tcp_sw_conn->sock->sk;
/* assign new callbacks */
......
tcp_sw_conn->old_write_space = sk->sk_write_space;
// assignment of "sk->sk_write_space" but after its value was assigned
to "tcp_sw_conn->old_write_space"...
sk->sk_write_space = iscsi_sw_tcp_write_space;
write_unlock_bh(&sk->sk_callback_lock);
}
Another question is: Now that we have "sk->sk_write_space =
iscsi_sw_tcp_write_space" why do we have to call "tcp_sw_conn-
old_write_space(sk);" in "iscsi_sw_tcp_write_space()"? Which function
We override it so the iscsi layer can start up its send code if needed,
and we call the old tcp function so it can do its processing (possibly
wake up threads waiting for space to open up).
is actually called when we do "tcp_sw_conn->old_write_space(sk);"?
And also in fuction "static void iscsi_sw_tcp_write_space(struct sock
*sk)", the last instruction is "iscsi_conn_queue_work(conn);". When I
trace down I found
inline void iscsi_conn_queue_work(struct iscsi_conn *conn)
{
struct Scsi_Host *shost = conn->session->host;
struct iscsi_host *ihost = shost_priv(shost);
if (ihost->workq)
queue_work(ihost->workq,&conn->xmitwork);
}
But I couldn't find more details about "queue_work(ihost->workq,&conn-
xmitwork);" in the source code (ver 2.0.871). Could anyone maybe
point me to the code of "queu_work"?
It is in the kernel source. Get the kernel and look at
kernel/workqueue.c. It basically wakes up a thread and has it process
some work. For iscsi it wakes up our xmit thread in case it had slept
due to there not being any write space.
--
You received this message because you are subscribed to the Google Groups
"open-iscsi" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/open-iscsi?hl=en.
