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

From: Pavel Emelyanov <[email-masked]>
Date: Tue, 22 Apr 2008 18:35:42 +0400

YOSHIFUJI Hideaki wrote:
> tcp4_seq_show() eats about 250 bytes.  By using buffer in seq_file
> directly, it will be reduced around 100 bytes.
> 
> One drawback is higher usage of slab for IPv6 but the format
> will not change with this patch.
> 
> Signed-off-by: YOSHIFUJI Hideaki <[email-masked]>

Plan C: we can follow the Al Viro's proposal about %n like in this patch.
The same applies to udp, fib (the /proc/net/route file), rt_cache and 
sctp debug. This is minus ~150-200 bytes for each.

How do you think?

Signed-off-by: Pavel Emelyanov <[email-masked]>

diff --git a/net/ipv4/fib_hash.c b/net/ipv4/fib_hash.c
index 02088de..2e2fc33 100644
--- a/net/ipv4/fib_hash.c
+++ b/net/ipv4/fib_hash.c
@@ -1003,7 +1003,7 @@ static unsigned fib_flag_trans(int type, __be32 mask, struct fib_info *fi)
 static int fib_seq_show(struct seq_file *seq, void *v)
 {
 	struct fib_iter_state *iter;
-	char bf[128];
+	int len;
 	__be32 prefix, mask;
 	unsigned flags;
 	struct fib_node *f;
@@ -1025,18 +1025,19 @@ static int fib_seq_show(struct seq_file *seq, void *v)
 	mask	= FZ_MASK(iter->zone);
 	flags	= fib_flag_trans(fa->fa_type, mask, fi);
 	if (fi)
-		snprintf(bf, sizeof(bf),
-			 "%s\t%08X\t%08X\t%04X\t%d\t%u\t%d\t%08X\t%d\t%u\t%u",
+		seq_printf(seq,
+			 "%s\t%08X\t%08X\t%04X\t%d\t%u\t%d\t%08X\t%d\t%u\t%u%n",
 			 fi->fib_dev ? fi->fib_dev->name : "*", prefix,
 			 fi->fib_nh->nh_gw, flags, 0, 0, fi->fib_priority,
 			 mask, (fi->fib_advmss ? fi->fib_advmss + 40 : 0),
 			 fi->fib_window,
-			 fi->fib_rtt >> 3);
+			 fi->fib_rtt >> 3, &len);
 	else
-		snprintf(bf, sizeof(bf),
-			 "*\t%08X\t%08X\t%04X\t%d\t%u\t%d\t%08X\t%d\t%u\t%u",
-			 prefix, 0, flags, 0, 0, 0, mask, 0, 0, 0);
-	seq_printf(seq, "%-127s\n", bf);
+		seq_printf(seq,
+			 "*\t%08X\t%08X\t%04X\t%d\t%u\t%d\t%08X\t%d\t%u\t%u%n",
+			 prefix, 0, flags, 0, 0, 0, mask, 0, 0, 0, &len);
+
+	seq_printf(seq, "%*s\n", 127 - len, "");
 out:
 	return 0;
 }
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index ea294ff..4b02d14 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -2602,15 +2602,16 @@ static int fib_route_seq_show(struct seq_file *seq, void *v)
 		list_for_each_entry_rcu(fa, &li->falh, fa_list) {
 			const struct fib_info *fi = fa->fa_info;
 			unsigned flags = fib_flag_trans(fa->fa_type, mask, fi);
-			char bf[128];
+			int len;
 
 			if (fa->fa_type == RTN_BROADCAST
 			    || fa->fa_type == RTN_MULTICAST)
 				continue;
 
 			if (fi)
-				snprintf(bf, sizeof(bf),
-					 "%s\t%08X\t%08X\t%04X\t%d\t%u\t%d\t%08X\t%d\t%u\t%u",
+				seq_printf(seq,
+					 "%s\t%08X\t%08X\t%04X\t%d\t%u\t"
+					 "%d\t%08X\t%d\t%u\t%u%n",
 					 fi->fib_dev ? fi->fib_dev->name : "*",
 					 prefix,
 					 fi->fib_nh->nh_gw, flags, 0, 0,
@@ -2619,14 +2620,15 @@ static int fib_route_seq_show(struct seq_file *seq, void *v)
 					 (fi->fib_advmss ?
 					  fi->fib_advmss + 40 : 0),
 					 fi->fib_window,
-					 fi->fib_rtt >> 3);
+					 fi->fib_rtt >> 3, &len);
 			else
-				snprintf(bf, sizeof(bf),
-					 "*\t%08X\t%08X\t%04X\t%d\t%u\t%d\t%08X\t%d\t%u\t%u",
+				seq_printf(seq,
+					 "*\t%08X\t%08X\t%04X\t%d\t%u\t"
+					 "%d\t%08X\t%d\t%u\t%u%n",
 					 prefix, 0, flags, 0, 0, 0,
-					 mask, 0, 0, 0);
+					 mask, 0, 0, 0, &len);
 
-			seq_printf(seq, "%-127s\n", bf);
+			seq_printf(seq, "%*s\n", 127 - len, "");
 		}
 	}
 
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 780e948..ce25a13 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -367,10 +367,10 @@ static int rt_cache_seq_show(struct seq_file *seq, void *v)
 			   "HHUptod\tSpecDst");
 	else {
 		struct rtable *r = v;
-		char temp[256];
+		int len;
 
-		sprintf(temp, "%s\t%08lX\t%08lX\t%8X\t%d\t%u\t%d\t"
-			      "%08lX\t%d\t%u\t%u\t%02X\t%d\t%1d\t%08X",
+		seq_printf(seq, "%s\t%08lX\t%08lX\t%8X\t%d\t%u\t%d\t"
+			      "%08lX\t%d\t%u\t%u\t%02X\t%d\t%1d\t%08X%n",
 			r->u.dst.dev ? r->u.dst.dev->name : "*",
 			(unsigned long)r->rt_dst, (unsigned long)r->rt_gateway,
 			r->rt_flags, atomic_read(&r->u.dst.__refcnt),
@@ -384,8 +384,9 @@ static int rt_cache_seq_show(struct seq_file *seq, void *v)
 			r->u.dst.hh ? atomic_read(&r->u.dst.hh->hh_refcnt) : -1,
 			r->u.dst.hh ? (r->u.dst.hh->hh_output ==
 				       dev_queue_xmit) : 0,
-			r->rt_spec_dst);
-		seq_printf(seq, "%-127s\n", temp);
+			r->rt_spec_dst, &len);
+
+		seq_printf(seq, "%*s\n", 127 - len, "");
 	}
 	return 0;
 }
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 7766151..0e9bc12 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2255,13 +2255,13 @@ void tcp_proc_unregister(struct net *net, struct tcp_seq_afinfo *afinfo)
 }
 
 static void get_openreq4(struct sock *sk, struct request_sock *req,
-			 char *tmpbuf, int i, int uid)
+			 struct seq_file *f, int i, int uid, int *len)
 {
 	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(f, "%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),
@@ -2276,10 +2276,11 @@ static void get_openreq4(struct sock *sk, struct request_sock *req,
 		0,  /* non standard timer */
 		0, /* open_requests have no inode */
 		atomic_read(&sk->sk_refcnt),
-		req);
+		req,
+		len);
 }
 
-static void get_tcp4_sock(struct sock *sk, char *tmpbuf, int i)
+static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i, int *len)
 {
 	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(f, "%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 :
@@ -2322,11 +2323,12 @@ static void get_tcp4_sock(struct sock *sk, char *tmpbuf, int i)
 		icsk->icsk_ack.ato,
 		(icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong,
 		tp->snd_cwnd,
-		tp->snd_ssthresh >= 0xFFFF ? -1 : tp->snd_ssthresh);
+		tp->snd_ssthresh >= 0xFFFF ? -1 : tp->snd_ssthresh,
+		len);
 }
 
 static void get_timewait4_sock(struct inet_timewait_sock *tw,
-			       char *tmpbuf, int i)
+			       struct seq_file *f, int i, int *len)
 {
 	__be32 dest, src;
 	__u16 destp, srcp;
@@ -2340,11 +2342,11 @@ 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(f, "%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);
+		atomic_read(&tw->tw_refcnt), tw, len);
 }
 
 #define TMPSZ 150
@@ -2352,7 +2354,7 @@ static void get_timewait4_sock(struct inet_timewait_sock *tw,
 static int tcp4_seq_show(struct seq_file *seq, void *v)
 {
 	struct tcp_iter_state* st;
-	char tmpbuf[TMPSZ + 1];
+	int len;
 
 	if (v == SEQ_START_TOKEN) {
 		seq_printf(seq, "%-*s\n", TMPSZ - 1,
@@ -2366,16 +2368,16 @@ 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(v, seq, st->num, &len);
 		break;
 	case TCP_SEQ_STATE_OPENREQ:
-		get_openreq4(st->syn_wait_sk, v, tmpbuf, st->num, st->uid);
+		get_openreq4(st->syn_wait_sk, v, seq, st->num, st->uid, &len);
 		break;
 	case TCP_SEQ_STATE_TIME_WAIT:
-		get_timewait4_sock(v, tmpbuf, st->num);
+		get_timewait4_sock(v, seq, st->num, &len);
 		break;
 	}
-	seq_printf(seq, "%-*s\n", TMPSZ - 1, tmpbuf);
+	seq_printf(seq, "%*s\n", TMPSZ - 1 - len, "");
 out:
 	return 0;
 }
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index b053ac7..1f535e3 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1619,7 +1619,8 @@ void udp_proc_unregister(struct net *net, struct udp_seq_afinfo *afinfo)
 }
 
 /* ------------------------------------------------------------------------ */
-static void udp4_format_sock(struct sock *sp, char *tmpbuf, int bucket)
+static void udp4_format_sock(struct sock *sp, struct seq_file *f,
+		int bucket, int *len)
 {
 	struct inet_sock *inet = inet_sk(sp);
 	__be32 dest = inet->daddr;
@@ -1627,13 +1628,13 @@ static void udp4_format_sock(struct sock *sp, char *tmpbuf, int bucket)
 	__u16 destp	  = ntohs(inet->dport);
 	__u16 srcp	  = ntohs(inet->sport);
 
-	sprintf(tmpbuf, "%4d: %08X:%04X %08X:%04X"
-		" %02X %08X:%08X %02X:%08lX %08X %5d %8d %lu %d %p",
+	seq_printf(f, "%4d: %08X:%04X %08X:%04X"
+		" %02X %08X:%08X %02X:%08lX %08X %5d %8d %lu %d %p%n",
 		bucket, src, srcp, dest, destp, sp->sk_state,
 		atomic_read(&sp->sk_wmem_alloc),
 		atomic_read(&sp->sk_rmem_alloc),
 		0, 0L, 0, sock_i_uid(sp), 0, sock_i_ino(sp),
-		atomic_read(&sp->sk_refcnt), sp);
+		atomic_read(&sp->sk_refcnt), sp, len);
 }
 
 int udp4_seq_show(struct seq_file *seq, void *v)
@@ -1644,11 +1645,11 @@ int udp4_seq_show(struct seq_file *seq, void *v)
 			   "rx_queue tr tm->when retrnsmt   uid  timeout "
 			   "inode");
 	else {
-		char tmpbuf[129];
 		struct udp_iter_state *state = seq->private;
+		int len;
 
-		udp4_format_sock(v, tmpbuf, state->bucket);
-		seq_printf(seq, "%-127s\n", tmpbuf);
+		udp4_format_sock(v, seq, state->bucket, &len);
+		seq_printf(seq, "%*s\n", 127 - len ,"");
 	}
 	return 0;
 }
diff --git a/net/sctp/objcnt.c b/net/sctp/objcnt.c
index cfeb07e..f73ec0e 100644
--- a/net/sctp/objcnt.c
+++ b/net/sctp/objcnt.c
@@ -83,13 +83,12 @@ static sctp_dbg_objcnt_entry_t sctp_dbg_objcnt[] = {
  */
 static int sctp_objcnt_seq_show(struct seq_file *seq, void *v)
 {
-	int i;
-	char temp[128];
+	int i, len;
 
 	i = (int)*(loff_t *)v;
-	sprintf(temp, "%s: %d", sctp_dbg_objcnt[i].label,
-				atomic_read(sctp_dbg_objcnt[i].counter));
-	seq_printf(seq, "%-127s\n", temp);
+	seq_printf(seq, "%s: %d%n", sctp_dbg_objcnt[i].label,
+				atomic_read(sctp_dbg_objcnt[i].counter), &len);
+	seq_printf(seq, "%*s\n", 127 - len, "");
 	return 0;
 }