logd: Limit ustream write buffer with configurable value

[Gocool..]

If the "logread" process is blocked in write call or stopped by
pressing "CTRL+Z", the logd starts to buffer all the messages
in the write buffer. Since there is no limit in w.max_buffers,
the logd consumes all the system memory at a point of time which
triggers Out Of Memory.
The ustream write max_buffer is limited with a configurable value
parsed through logd with option "-W" and unlimited if value is '0'.

Similar ticket has been reported in,
https://github.com/openwrt/packages/issues/5604

Signed-off-by: gokulnathan <gokulmrt at gmail.com>

diff --git a/log/logd.c b/log/logd.c
index 5d6c458..7e52820 100644
--- a/log/logd.c
+++ b/log/logd.c
@@ -33,6 +33,8 @@ static struct blob_buf b;
 static struct ubus_auto_conn conn;
 static LIST_HEAD(clients);

+static unsigned int log_ustream_max_buffers = 0;
+
 enum {
        READ_LINES,
        READ_STREAM,
@@ -130,6 +132,11 @@ read_log(struct ubus_context *ctx, struct ubus_object *obj,
                cl->s.stream.notify_state = client_notify_state;
                cl->fd = fds[1];
                ustream_fd_init(&cl->s, cl->fd);
+               /* Limit the ustream write max_buffers to avoid
infinite memory consumption when no logread happens */
+               if (0 != log_ustream_max_buffers)
+               {
+                       cl->s.stream.w.max_buffers = log_ustream_max_buffers;
+               }
                list_add(&cl->list, &clients);
                while ((!tb[READ_LINES] || count) && l) {
                        blob_buf_init(&b, 0);
@@ -243,13 +250,18 @@ main(int argc, char **argv)
        struct passwd *p = NULL;

        signal(SIGPIPE, SIG_IGN);
-       while ((ch = getopt(argc, argv, "S:")) != -1) {
+       while ((ch = getopt(argc, argv, "S:W:")) != -1) {
                switch (ch) {
                case 'S':
                        log_size = atoi(optarg);
                        if (log_size < 1)
                                log_size = 16;
                        break;
+               case 'W':
+                       log_ustream_max_buffers = atoi(optarg);
+                       if (log_ustream_max_buffers < 1)
+                               log_ustream_max_buffers = 0;
+                       break;
                }
        }
        log_size *= 1024;