From: Kienan Stewart <kstewart@efficios.com>
Date: Wed, 22 Nov 2023 16:18:23 +0000 (-0500)
Subject: sessiond: log error message when libkmod operations fail
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=7d46777ba0eaba7916ae822a7133f39740cdf9e5;p=lttng-tools.git

sessiond: log error message when libkmod operations fail

Issue observed
--------------

When loading or unloading modules and libkmod is being used, there are
no details available in the `lttng-sessiond` error ouput.

For example,

```
$ sudo -E lttng-sessiond
Error: Unable to load required module lttng-ring-buffer-client-discard
Warning: No kernel tracer available
```

When libkmod is not available or disabled in the configuration
options, `lttng-sessiond` falls back to invoking `modprobe` via a
`system` call. The command's error output will be visible and provide
the necessary details, eg.

```
$ sudo -E lttng-sessiond
modprobe: FATAL: Module lttng-ring-buffer-client-discard not found in directory /usr/lib/modules/6.2.0-36-generic
Error: Unable to load required module lttng-ring-buffer-client-discard
Warning: No kernel tracer available
```

Solution
--------

Include the error message from `strerror` in the message that is
logged via the `DBG` or `ERR` macros.

The error is no clearer for users, eg.

```
$ sudo -E lttng-sessiond
PERROR - 12:00:05.004593045 [Main]: Unable to load required module
lttng-ring-buffer-client-discard: No such file or directory (in
modprobe_lttng() at modprobe.cpp:396)
Warning: No kernel tracer available
```

Known drawbacks
---------------

The debug message emitted when a non-obligatory kernel module fails to
load is now printed with `PERROR`.

Change-Id: Ibd25614a6c5b5dd3b801063eafc272a4017058cd
Signed-off-by: Kienan Stewart <kstewart@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/src/bin/lttng-sessiond/modprobe.cpp b/src/bin/lttng-sessiond/modprobe.cpp
index ac9f14257..547756de9 100644
--- a/src/bin/lttng-sessiond/modprobe.cpp
+++ b/src/bin/lttng-sessiond/modprobe.cpp
@@ -393,11 +393,11 @@ static int modprobe_lttng(struct kern_modules_param *modules, int entries)
 			ret = 0;
 		} else if (ret < 0) {
 			if (modules[i].load_policy == KERNEL_MODULE_PROPERTY_LOAD_POLICY_REQUIRED) {
-				ERR("Unable to load required module %s", modules[i].name);
+				PERROR("Unable to load required module `%s`", modules[i].name)
 				goto error;
 			} else {
-				DBG("Unable to load optional module %s; continuing",
-				    modules[i].name);
+				PERROR("Unable to load optional module `%s`; continuing",
+				       modules[i].name);
 				ret = 0;
 			}
 		} else {
@@ -491,7 +491,7 @@ static void modprobe_remove_lttng(const struct kern_modules_param *modules, int
 			DBG("Module %s is not in kernel.", modules[i].name);
 		} else if (modules[i].load_policy == KERNEL_MODULE_PROPERTY_LOAD_POLICY_REQUIRED &&
 			   ret < 0) {
-			ERR("Unable to remove module %s", modules[i].name);
+			PERROR("Unable to remove module `%s`", modules[i].name);
 		} else {
 			DBG("Modprobe removal successful %s", modules[i].name);
 		}