Introduce ustctl_write_one_packet_to_channel

[lttng-ust.git] / liblttng-ust-ctl / ustctl.c

diff --git a/liblttng-ust-ctl/ustctl.c b/liblttng-ust-ctl/ustctl.c
index 0361f184e342619031ec51d837c509743c7bab77..28dee5e9cdf80118113f53522dc296460f66b1af 100644 (file)
--- a/liblttng-ust-ctl/ustctl.c
+++ b/liblttng-ust-ctl/ustctl.c
@@ -1054,6 +1054,40 @@ end:
        return ret;
 }
 
+/*
+ * Write at most one packet in the channel.
+ * Returns the number of bytes written on success, < 0 on error.
+ */
+ssize_t ustctl_write_one_packet_to_channel(
+               struct ustctl_consumer_channel *channel,
+               const char *metadata_str,       /* NOT null-terminated */
+               size_t len)                     /* metadata length */
+{
+       struct lttng_ust_lib_ring_buffer_ctx ctx;
+       struct lttng_channel *chan = channel->chan;
+       const char *str = metadata_str;
+       ssize_t reserve_len;
+       int ret;
+
+       reserve_len = min_t(ssize_t,
+                       chan->ops->packet_avail_size(chan->chan, chan->handle),
+                       len);
+       lib_ring_buffer_ctx_init(&ctx, chan->chan, NULL, reserve_len,
+                       sizeof(char), -1, chan->handle);
+       ret = chan->ops->event_reserve(&ctx, 0);
+       if (ret != 0) {
+               DBG("LTTng: event reservation failed");
+               assert(ret < 0);
+               reserve_len = ret;
+               goto end;
+       }
+       chan->ops->event_write(&ctx, str, reserve_len);
+       chan->ops->event_commit(&ctx);
+
+end:
+       return reserve_len;
+}
+
 int ustctl_channel_close_wait_fd(struct ustctl_consumer_channel *consumer_chan)
 {
        struct channel *chan;