From 1fd0c9b0e1f27098f9bf86e86285335e640317a5 Mon Sep 17 00:00:00 2001
From: Stefano Brivio <sbrivio@redhat.com>
Date: Fri, 15 Oct 2021 22:39:17 +0200
Subject: util, pasta: Don't read() and lseek() every single line in
 read_line()

...periodically checking bound ports becomes quite expensive
otherwise.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 conf.c |  2 +-
 util.c | 27 +++++++++++++++++++++++----
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/conf.c b/conf.c
index b92a7d9..b91d09b 100644
--- a/conf.c
+++ b/conf.c
@@ -293,7 +293,7 @@ static void get_dns(struct ctx *c)
 	if ((fd = open("/etc/resolv.conf", O_RDONLY)) < 0)
 		goto out;
 
-	while (line_read(buf, BUFSIZ, fd)) {
+	while (!(*buf = 0) && line_read(buf, BUFSIZ, fd)) {
 		if (!dns_set && strstr(buf, "nameserver ") == buf) {
 			p = strrchr(buf, ' ');
 			if (!p)
diff --git a/util.c b/util.c
index 0a05ffb..016749c 100644
--- a/util.c
+++ b/util.c
@@ -368,8 +368,8 @@ int bitmap_isset(uint8_t *map, int bit)
 }
 
 /**
- * line_read() - Same as fgets(), without using heap, a file instead of a stream
- * @buf:	Read buffer
+ * line_read() - Similar to fgets(), no heap usage, a file instead of a stream
+ * @buf:	Read buffer: on non-empty string, use that instead of reading
  * @len:	Maximum line length
  * @fd:		File descriptor for reading
  *
@@ -377,14 +377,31 @@ int bitmap_isset(uint8_t *map, int bit)
  */
 char *line_read(char *buf, size_t len, int fd)
 {
+	int n, do_read = !*buf;
 	char *p;
-	int n;
+
+	if (!do_read) {
+		char *nl;
+
+		buf[len - 1] = 0;
+		if (!strlen(buf))
+			return NULL;
+
+		p = buf + strlen(buf) + 1;
+
+		if (!(nl = strchr(p, '\n')))
+			return NULL;
+		*nl = 0;
+
+		return memmove(buf, p, len - (p - buf));
+	}
 
 	n = read(fd, buf, --len);
 	if (n <= 0)
 		return NULL;
 
 	buf[len] = 0;
+
 	if (!(p = strchr(buf, '\n')))
 		return buf;
 
@@ -393,6 +410,7 @@ char *line_read(char *buf, size_t len, int fd)
 		return buf;
 
 	lseek(fd, (p - buf) - n + 1, SEEK_CUR);
+
 	return buf;
 }
 
@@ -404,7 +422,7 @@ char *line_read(char *buf, size_t len, int fd)
  */
 void procfs_scan_listen(char *name, uint8_t *map, uint8_t *exclude)
 {
-	char line[200], path[PATH_MAX];
+	char line[BUFSIZ], path[PATH_MAX];
 	unsigned long port;
 	unsigned int state;
 	int fd;
@@ -413,6 +431,7 @@ void procfs_scan_listen(char *name, uint8_t *map, uint8_t *exclude)
 	if ((fd = open(path, O_RDONLY)) < 0)
 		return;
 
+	*line = 0;
 	line_read(line, sizeof(line), fd);
 	while (line_read(line, sizeof(line), fd)) {
 		if (sscanf(line, "%*u: %*x:%lx %*x:%*x %x", &port, &state) != 2)
-- 
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