X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=blobdiff_plain;f=src%2Fbin%2Flttng-sessiond%2Fust-registry.h;h=2940ab7accea9534b3fe63696f4b5ea6a60a55e6;hp=414975cafc4b1f3b209e49ce5900c7373e18f2dd;hb=9c9d917cfe2e6a9f35ef82cb64e442451210716f;hpb=e9404c27e7cc9d841785e6c4292c1add19fbc1cc

diff --git a/src/bin/lttng-sessiond/ust-registry.h b/src/bin/lttng-sessiond/ust-registry.h
index 414975caf..2940ab7ac 100644
--- a/src/bin/lttng-sessiond/ust-registry.h
+++ b/src/bin/lttng-sessiond/ust-registry.h
@@ -71,6 +71,32 @@ struct ust_registry_session {
 	/* Current version of the metadata. */
 	uint64_t metadata_version;
 
+	/*
+	 * Those fields are only used when a session is created with
+	 * the --shm-path option. In this case, the metadata is output
+	 * twice: once to the consumer, as ususal, but a second time
+	 * also in the shm path directly. This is done so that a copy
+	 * of the metadata that is as fresh as possible is available
+	 * on the event of a crash.
+	 *
+	 * root_shm_path contains the shm-path provided by the user, along with
+	 * the session's name and timestamp:
+	 *   e.g. /tmp/my_shm/my_session-20180612-135822
+	 *
+	 * shm_path contains the full path of the memory buffers:
+	 *   e.g. /tmp/my_shm/my_session-20180612-135822/ust/uid/1000/64-bit
+	 *
+	 * metadata_path contains the full path to the metadata file that
+	 * is kept for the "crash buffer" extraction:
+	 *  e.g. /tmp/my_shm/my_session-20180612-135822/ust/uid/1000/64-bit/metadata
+	 *
+	 * Note that this is not the trace's final metadata file. It is
+	 * only meant to be used to read the contents of the ring buffers
+	 * in the event of a crash.
+	 *
+	 * metadata_fd is a file descriptor that points to the file at
+	 * 'metadata_path'.
+	 */
 	char root_shm_path[PATH_MAX];
 	char shm_path[PATH_MAX];
 	char metadata_path[PATH_MAX];