contrib/dmesg: add script to dump kernel log

This script dumps the kernel log.

Signed-off-by: Kuan-Ying Lee <[email protected]>

contrib/dmesg.py

@@ -0,0 +1,62 @@
+#!/usr/bin/env drgn
+# Copyright (c) Canonical Ltd.
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+""" Script to dump kernel log using drgn """
+
+desc_ring = prog["prb"].desc_ring
+text_data_ring = prog["prb"].text_data_ring
+
+descs_count = 1 << desc_ring.count_bits
+descs = desc_ring.descs
+infos = desc_ring.infos
+
+data_size = 1 << text_data_ring.size_bits
+data = text_data_ring.data
+
+desc_committed = prog.type("enum desc_state").enumerators[2].value
+desc_finalized = prog.type("enum desc_state").enumerators[3].value
+
+tail_id = desc_ring.tail_id.counter
+head_id = desc_ring.head_id.counter
+
+DESC_SV_BITS = prog.type("unsigned long").size * 8
+DESC_FLAGS_SHIFT = DESC_SV_BITS - 2
+DESC_FLAGS_MASK = 3 << DESC_FLAGS_SHIFT
+DESC_ID_MASK = ~DESC_FLAGS_MASK
+
+
+def DESC_STATE(sv):
+    return 3 & (sv >> DESC_FLAGS_SHIFT)
+
+
+cur_id = tail_id
+while True:
+    i = cur_id % descs_count
+    state = DESC_STATE(descs[i].state_var.counter)
+    if state != desc_committed and state != desc_finalized:
+        if cur_id == head_id:
+            break
+        cur_id = (cur_id + 1) & DESC_ID_MASK
+        continue
+    begin = descs[i].text_blk_lpos.begin % data_size
+    end = descs[i].text_blk_lpos.next % data_size
+
+    if begin & 1 == 1:
+        text = ""
+    else:
+        if begin > end:
+            begin = 0
+        text_start = begin + prog.type("unsigned long").size
+        text_len = infos[i].text_len
+
+        if end - text_start < text_len:
+            text_len = end - text_start
+        text = data[text_start].address_of_().string_()[0:text_len].decode("utf8")
+    time_stamp = infos[i].ts_nsec
+    for line in text.splitlines():
+        time = (time_stamp / 1000000000.0).value_()
+        print(f"[{time:12.6f}] {line}")
+    if cur_id == head_id:
+        break
+    cur_id = (cur_id + 1) & DESC_ID_MASK