[advance-reboot] Support log_analyzer support on small disk devices (s…

…onic-net#5126)

Presently, test_advanced_reboot cases fail on small disk device since preboot logs are not retained and log_analyzer
fails to get start strings from the logs.
Fix this issue so that test_advanced_reboot cases can be executed on small disk devices.
How did you do it?
Steps:
1. Create a back of warm/fast-reboot script.
2. Before reboot - modify script and add step to copy logs from /var/log to /host before kexec.
3. After reboot - collect the backup logs from /host/ and restore the warm/fast-reboot script.
Tested on a physical testbed with small HD. Timing data for reboot analysis can be collected now.

tests/platform_tests/conftest.py

@@ -18,6 +18,11 @@
 TEMPLATES_DIR = os.path.join(os.path.dirname(os.path.realpath(__file__)), "templates")
 FMT = "%b %d %H:%M:%S.%f"
 FMT_SHORT = "%b %d %H:%M:%S"
+SMALL_DISK_SKUS = [
+    "Arista-7060CX-32S-C32",
+    "Arista-7060CX-32S-Q32"
+]
+
 
 def _parse_timestamp(timestamp):
     try:
@@ -330,6 +335,23 @@ def verify_mac_jumping(test_name, timing_data):
             pytest.fail("Mac expiry detected during the window when FDB ageing was disabled")
 
 
+def overwrite_script_to_backup_logs(duthost, reboot_type):
+    # find the fast/warm-reboot script path
+    reboot_script_path = duthost.shell('which {}'.format("{}-reboot".format(reboot_type)))['stdout']
+    # backup original script
+    duthost.shell("cp {} {}".format(reboot_script_path, reboot_script_path + ".orig"))
+    # find the anchor string inside fast/warm-reboot script
+    rebooting_log_line = "debug.*Rebooting with.*to.*"
+    # Create a backup log command to be inserted right after the anchor string defined above
+    backup_log_cmds ="cp /var/log/syslog /host/syslog.99;" +\
+        "cp /var/log/swss/sairedis.rec /host/sairedis.rec.99;" +\
+        "cp /var/log/swss/swss.rec /host/swss.rec.99;" +\
+            "cp /var/log/frr/bgpd.log /host/bgpd.log.99"
+    # Do find-and-replace on fast/warm-reboot script to insert the backup_log_cmds string
+    insert_backup_command = "sed -i '/{}/a {}' {}".format(rebooting_log_line, backup_log_cmds, reboot_script_path)
+    duthost.shell(insert_backup_command)
+
+
 @pytest.fixture()
 def advanceboot_loganalyzer(duthosts, rand_one_dut_hostname, request):
     """
@@ -356,6 +378,14 @@ def advanceboot_loganalyzer(duthosts, rand_one_dut_hostname, request):
         if 'vs' not in device_marks:
             pytest.skip('Testcase not supported for kvm')
 
+    hwsku = duthost.facts["hwsku"]
+    if hwsku in SMALL_DISK_SKUS:
+        # For small disk devices, /var/log in mounted in tmpfs.
+        # Hence, after reboot the preboot logs are lost.
+        # For log_analyzer to work, it needs logs from the shutdown path
+        # Below method inserts a step in reboot script to back up logs to /host/
+        overwrite_script_to_backup_logs(duthost, reboot_type)
+
     loganalyzer = LogAnalyzer(ansible_host=duthost, marker_prefix="test_advanced_reboot_{}".format(test_name),
                     additional_files={'/var/log/swss/sairedis.rec': 'recording on: /var/log/swss/sairedis.rec', '/var/log/frr/bgpd.log': ''})
 
@@ -375,6 +405,17 @@ def pre_reboot_analysis():
         return marker
 
     def post_reboot_analysis(marker, reboot_oper=None, log_dir=None):
+        if hwsku in SMALL_DISK_SKUS:
+            restore_backup = "mv /host/syslog.99 /var/log/; " +\
+                "mv /host/sairedis.rec.99 /var/log/swss/; " +\
+                    "mv /host/swss.rec.99 /var/log/swss/; " +\
+                        "mv /host/bgpd.log.99 /var/log/frr/"
+            # find the fast/warm-reboot script path
+            reboot_script_path = duthost.shell('which {}'.format("{}-reboot".format(reboot_type)))['stdout']
+            # restore original script
+            duthost.shell("mv {} {}".format(reboot_script_path + ".orig", reboot_script_path))
+            duthost.shell(restore_backup, module_ignore_errors=True)
+
         result = loganalyzer.analyze(marker, fail=False)
         analyze_result = {"time_span": dict(), "offset_from_kexec": dict()}
         offset_from_kexec = dict()