[RFC PATCH net-2.6.26 (Plan A)] [TCP]: Lower stack usage in tcp4_seq_show().

[RFC PATCH net-2.6.26 (Plan A)] [TCP]: Lower stack usage in tcp4_seq_show().

[YOSHIFUJI Hideaki / 吉藤英明]

tcp4_seq_show() eats about 250 bytes.  By using buffer in seq_file
directly, it will be reduced under 100 bytes.

One drawback is slight change of the format - the format was fixed
size and now its size is variable.
However, size of the line was 128 bytes in 2.2, and 150 bytes in 2.6,
so the change may not matter, probably.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>

--- 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 7766151..e3a6832 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2254,14 +2254,15 @@ void tcp_proc_unregister(struct net *net, struct tcp_seq_afinfo *afinfo)
 	proc_net_remove(net, afinfo->name);
 }
 
-static void get_openreq4(struct sock *sk, struct request_sock *req,
-			 char *tmpbuf, int i, int uid)
+static void get_openreq4(struct seq_file *seq, struct sock *sk,
+			 struct request_sock *req,
+			 int i, int uid)
 {
 	const struct inet_request_sock *ireq = inet_rsk(req);
 	int ttd = req->expires - jiffies;
 
-	sprintf(tmpbuf, "%4d: %08X:%04X %08X:%04X"
-		" %02X %08X:%08X %02X:%08lX %08X %5d %8d %u %d %p",
+	seq_printf(seq, "%4d: %08X:%04X %08X:%04X"
+		" %02X %08X:%08X %02X:%08lX %08X %5d %8d %u %d %p\n",
 		i,
 		ireq->loc_addr,
 		ntohs(inet_sk(sk)->sport),
@@ -2279,7 +2280,7 @@ static void get_openreq4(struct sock *sk, struct request_sock *req,
 		req);
 }
 
-static void get_tcp4_sock(struct sock *sk, char *tmpbuf, int i)
+static void get_tcp4_sock(struct seq_file *seq, struct sock *sk, int i)
 {
 	int timer_active;
 	unsigned long timer_expires;
@@ -2305,8 +2306,8 @@ static void get_tcp4_sock(struct sock *sk, char *tmpbuf, int i)
 		timer_expires = jiffies;
 	}
 
-	sprintf(tmpbuf, "%4d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX "
-			"%08X %5d %8d %lu %d %p %u %u %u %u %d",
+	seq_printf(seq, "%4d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX "
+			"%08X %5d %8d %lu %d %p %u %u %u %u %d\n",
 		i, src, srcp, dest, destp, sk->sk_state,
 		tp->write_seq - tp->snd_una,
 		sk->sk_state == TCP_LISTEN ? sk->sk_ack_backlog :
@@ -2325,8 +2326,8 @@ static void get_tcp4_sock(struct sock *sk, char *tmpbuf, int i)
 		tp->snd_ssthresh >= 0xFFFF ? -1 : tp->snd_ssthresh);
 }
 
-static void get_timewait4_sock(struct inet_timewait_sock *tw,
-			       char *tmpbuf, int i)
+static void get_timewait4_sock(struct seq_file *seq, struct inet_timewait_sock *tw,
+			       int i)
 {
 	__be32 dest, src;
 	__u16 destp, srcp;
@@ -2340,25 +2341,22 @@ static void get_timewait4_sock(struct inet_timewait_sock *tw,
 	destp = ntohs(tw->tw_dport);
 	srcp  = ntohs(tw->tw_sport);
 
-	sprintf(tmpbuf, "%4d: %08X:%04X %08X:%04X"
-		" %02X %08X:%08X %02X:%08lX %08X %5d %8d %d %d %p",
+	seq_printf(seq, "%4d: %08X:%04X %08X:%04X"
+		" %02X %08X:%08X %02X:%08lX %08X %5d %8d %d %d %p\n",
 		i, src, srcp, dest, destp, tw->tw_substate, 0, 0,
 		3, jiffies_to_clock_t(ttd), 0, 0, 0, 0,
 		atomic_read(&tw->tw_refcnt), tw);
 }
 
-#define TMPSZ 150
-
 static int tcp4_seq_show(struct seq_file *seq, void *v)
 {
 	struct tcp_iter_state* st;
-	char tmpbuf[TMPSZ + 1];
 
 	if (v == SEQ_START_TOKEN) {
-		seq_printf(seq, "%-*s\n", TMPSZ - 1,
-			   "  sl  local_address rem_address   st tx_queue "
-			   "rx_queue tr tm->when retrnsmt   uid  timeout "
-			   "inode");
+		seq_puts(seq,
+			 "  sl  local_address rem_address   st tx_queue "
+			 "rx_queue tr tm->when retrnsmt   uid  timeout "
+			 "inode\n");
 		goto out;
 	}
 	st = seq->private;
@@ -2366,16 +2364,15 @@ static int tcp4_seq_show(struct seq_file *seq, void *v)
 	switch (st->state) {
 	case TCP_SEQ_STATE_LISTENING:
 	case TCP_SEQ_STATE_ESTABLISHED:
-		get_tcp4_sock(v, tmpbuf, st->num);
+		get_tcp4_sock(seq, v, st->num);
 		break;
 	case TCP_SEQ_STATE_OPENREQ:
-		get_openreq4(st->syn_wait_sk, v, tmpbuf, st->num, st->uid);
+		get_openreq4(seq, st->syn_wait_sk, v, st->num, st->uid);
 		break;
 	case TCP_SEQ_STATE_TIME_WAIT:
-		get_timewait4_sock(v, tmpbuf, st->num);
+		get_timewait4_sock(seq, v, st->num);
 		break;
 	}
-	seq_printf(seq, "%-*s\n", TMPSZ - 1, tmpbuf);
 out:
 	return 0;
 }

-- 
YOSHIFUJI Hideaki @ USAGI Project  <yoshfuji@linux-ipv6.org>
GPG-FP  : 9022 65EB 1ECF 3AD1 0BDF  80D8 4807 F894 E062 0EEA

Re: [RFC PATCH net-2.6.26 (Plan A)] [TCP]: Lower stack usage in tcp4_seq_show().

[Al Viro]

On Tue, Apr 15, 2008 at 07:24:34PM +0900, YOSHIFUJI Hideaki / ?$B5HF#1QL@ wrote:
> tcp4_seq_show() eats about 250 bytes.  By using buffer in seq_file
> directly, it will be reduced under 100 bytes.
> 
> One drawback is slight change of the format - the format was fixed
> size and now its size is variable.
> However, size of the line was 128 bytes in 2.2, and 150 bytes in 2.6,
> so the change may not matter, probably.

> -	sprintf(tmpbuf, "%4d: %08X:%04X %08X:%04X"
> -		" %02X %08X:%08X %02X:%08lX %08X %5d %8d %u %d %p",
> +	seq_printf(seq, "%4d: %08X:%04X %08X:%04X"
> +		" %02X %08X:%08X %02X:%08lX %08X %5d %8d %u %d %p\n",

Or you can just do
	int len;
	...
	seq_printf(seq, "%4d: %08X:%04X %08X:%04X"
		" %02X %08X:%08X %02X:%08lX %08X %5d %8d %u %d %p%n",
>  		i,
>  		ireq->loc_addr,
>  		ntohs(inet_sk(sk)->sport),
		...,
		&len);
	seq_printf("%*s\n", TMPSZ - 1 - len, "");

and be done with that, keeping the output unchanged.  That's exactly what
%n is for - it allows to get the width of output so far, precisely for
such situations.