X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=blobdiff_plain;f=src%2Fbin%2Flttng-sessiond%2Fchannel.c;h=88480c4b4e7b78fd63a2edc744618eadba0c36bc;hp=8ceb4e8930321ed947ea1216c782558811f0b753;hb=8d5841ea483139d3ab2f2b4dd39263dad63832b1;hpb=b63d638bfff6105d7de7fe88792b79148990bc39

diff --git a/src/bin/lttng-sessiond/channel.c b/src/bin/lttng-sessiond/channel.c
index 8ceb4e893..88480c4b4 100644
--- a/src/bin/lttng-sessiond/channel.c
+++ b/src/bin/lttng-sessiond/channel.c
@@ -179,6 +179,19 @@ error:
 	return ret;
 }
 
+static int channel_validate(struct lttng_channel *attr)
+{
+	/*
+	 * The ringbuffer (both in user space and kernel) behaves badly
+	 * in overwrite mode and with less than 2 subbuffers so block it
+	 * right away and send back an invalid attribute error.
+	 */
+	if (attr->attr.overwrite && attr->attr.num_subbuf < 2) {
+		return -1;
+	}
+	return 0;
+}
+
 /*
  * Create kernel channel of the kernel session and notify kernel thread.
  */
@@ -201,12 +214,25 @@ int channel_kernel_create(struct ltt_kernel_session *ksession,
 		attr = defattr;
 	}
 
+	/*
+	 * Set the overwrite mode for this channel based on the session
+	 * type unless the client explicitly overrides the channel mode.
+	 */
+	if (attr->attr.overwrite == DEFAULT_CHANNEL_OVERWRITE) {
+		attr->attr.overwrite = !!ksession->snapshot_mode;
+	}
+
+	/* Enforce mmap output for snapshot sessions. */
 	if (ksession->snapshot_mode) {
-		/* Force channel attribute for snapshot mode. */
-		attr->attr.overwrite = 1;
 		attr->attr.output = LTTNG_EVENT_MMAP;
 	}
 
+	/* Validate common channel properties. */
+	if (channel_validate(attr) < 0) {
+		ret = LTTNG_ERR_INVALID;
+		goto error;
+	}
+
 	/* Channel not found, creating it */
 	ret = kernel_create_channel(ksession, attr);
 	if (ret < 0) {
@@ -299,12 +325,25 @@ int channel_ust_create(struct ltt_ust_session *usess,
 		}
 	}
 
+	/*
+	 * Set the overwrite mode for this channel based on the session
+	 * type unless the client explicitly overrides the channel mode.
+	 */
+	if (attr->attr.overwrite == DEFAULT_CHANNEL_OVERWRITE) {
+		attr->attr.overwrite = !!usess->snapshot_mode;
+	}
+
+	/* Enforce mmap output for snapshot sessions. */
 	if (usess->snapshot_mode) {
-		/* Force channel attribute for snapshot mode. */
-		attr->attr.overwrite = 1;
 		attr->attr.output = LTTNG_EVENT_MMAP;
 	}
 
+	/* Validate common channel properties. */
+	if (channel_validate(attr) < 0) {
+		ret = LTTNG_ERR_INVALID;
+		goto error;
+	}
+
 	/*
 	 * Validate UST buffer size and number of buffers: must both be power of 2
 	 * and nonzero. We validate right here for UST, because applications will