Sentinel

This is the repository for the Sentinel Kernel Module (SKM). Its role is to expose system-level metrics to userspace, by interfacing directly with the kernel

Install

All the commands have to be run as root

• Install the Linux Kernel headers for your system
• Build the module with make
• Install the module with make install
• Enable auto-load with echo "sentinel" >> /etc/modules-load.d/modules.conf

Adding new metrics

There are a few places to edit to insert new metrics in the SKM.

• Create a new file entry in /sys/kernel/sentinel with the sentinel_sysfs.c/init_attr_group() function, by adding a new case to the switch statement. The new entry should look like:

case $X:
    sprintf(buf, "$NEW_METRIC_NAME");
    break;

where $X is the next number after the last case statemement, and $NEW_METRIC_NAME is the name of the file that should be created.

• Set the sentinel_helper.c/NB_FILES_NOT_CPU macro as $X+1.

• Edit the contents of sentinel_helper.h/data_t to add a new field for your metric.

• Edit the sentinel_helper.c/populate_data() or sentinel_helper.c/get_process_data() functions to fill the new fields with the corresponding data.

• Add a new else if statement to sentinel_sysfs.c/sentinel_sysfs_show() that formats and returns the value of your metric. The statement should look like:

else if (strcmp(attr->attr.name, "$NEW_METRIC_NAME") == 0) {
    return sprintf(buf, "$FORMAT_STRING\n", data.$FIELD_NAME);

where $FORMAT_STRING is the formatting to use, and $FIELD_NAME is the identifier of the metric field in the data_t structure.

• (Optional) If your metric should be writeable (to configure the SKM for instance), edit the sentinel_sysfs.c/sentinel_sysfs_store() to add a new else if statement that handles it. The statement should look like:

else if (strcmp(attr->attr.name, "$NEW_METRIC_NAME") == 0) {
    // Store or use the data
    return len;

Possible improvements

• Only collect the value of the metric that was read, instead of gathering everything everytime.
• Make the code more modular to allow for easier metric adding (insetad of relying on the clunky switch-case and else-if statements everywhere)