192 lines
6.2 KiB
Diff
192 lines
6.2 KiB
Diff
commit feae3d1754d2b0788ce1f18b0cd4b40098ff52ff
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Author: Philipp Rudo <prudo@redhat.com>
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Date: Mon Mar 14 17:04:29 2022 +0100
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[PATCH v2 1/3] add generic cycle detection
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In order to work makedumpfile needs to interpret data read from the
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dump. This can cause problems as the data from the dump cannot be
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trusted (otherwise the kernel wouldn't have panicked in the first
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place). This also means that every loop which stop condition depend on
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data read from the dump has a chance to loop forever. Thus add a generic
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cycle detection mechanism that allows to detect and handle such
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situations appropriately.
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For cycle detection use Brent's algorithm [1] as it has constant memory
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usage. With this it can also be used in the kdump kernel without the
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danger that it runs oom when iterating large data structures.
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Furthermore it only depends on some pointer arithmetic. Thus the
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performance impact (as long as no cycle was detected) should be
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comparatively small.
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[1] https://en.wikipedia.org/wiki/Cycle_detection#Brent's_algorithm
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Suggested-by: Dave Wysochanski <dwysocha@redhat.com>
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Signed-off-by: Philipp Rudo <prudo@redhat.com>
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Reviewed-and-tested-by: Dave Wysochanski <dwysocha@redhat.com>
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diff --git a/makedumpfile-1.7.0/Makefile b/makedumpfile-1.7.0/Makefile
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index f118b31e45989d9590ae075fb9b8ed2f27353a92..3441364cb6c7103a20072bd50ec58f1eed01ab69 100644
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--- a/makedumpfile-1.7.0/Makefile
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+++ b/makedumpfile-1.7.0/Makefile
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@@ -45,7 +45,7 @@ CFLAGS_ARCH += -m32
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endif
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SRC_BASE = makedumpfile.c makedumpfile.h diskdump_mod.h sadump_mod.h sadump_info.h
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-SRC_PART = print_info.c dwarf_info.c elf_info.c erase_info.c sadump_info.c cache.c tools.c printk.c
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+SRC_PART = print_info.c dwarf_info.c elf_info.c erase_info.c sadump_info.c cache.c tools.c printk.c detect_cycle.c
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OBJ_PART=$(patsubst %.c,%.o,$(SRC_PART))
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SRC_ARCH = arch/arm.c arch/arm64.c arch/x86.c arch/x86_64.c arch/ia64.c arch/ppc64.c arch/s390x.c arch/ppc.c arch/sparc64.c arch/mips64.c
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OBJ_ARCH=$(patsubst %.c,%.o,$(SRC_ARCH))
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diff --git a/makedumpfile-1.7.0/detect_cycle.c b/makedumpfile-1.7.0/detect_cycle.c
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new file mode 100644
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index 0000000000000000000000000000000000000000..6b551a75d1c83d64fba2c078be8133efbc791fbe
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--- /dev/null
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+++ b/makedumpfile-1.7.0/detect_cycle.c
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@@ -0,0 +1,99 @@
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+/*
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+ * detect_cycle.c -- Generic cycle detection using Brent's algorithm
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+ *
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+ * Created by: Philipp Rudo <prudo@redhat.com>
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+ *
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+ * Copyright (c) 2022 Red Hat, Inc. All rights reserved.
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+ *
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+ * This program is free software; you can redistribute it and/or modify
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+ * it under the terms of the GNU General Public License as published by
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+ * the Free Software Foundation; either version 2 of the License, or
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+ * (at your option) any later version.
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+ *
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+ * This program is distributed in the hope that it will be useful,
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+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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+ * GNU General Public License for more details.
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+ */
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+
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+#include <stdlib.h>
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+
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+#include "detect_cycle.h"
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+
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+struct detect_cycle {
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+ /* First entry of the list */
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+ void *head;
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+
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+ /* Variables required by Brent's algorithm */
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+ void *fast_p;
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+ void *slow_p;
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+ unsigned long length;
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+ unsigned long power;
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+
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+ /* Function to get the next entry in the list */
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+ dc_next_t next;
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+
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+ /* Private data passed to next */
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+ void *data;
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+};
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+
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+struct detect_cycle *dc_init(void *head, void *data, dc_next_t next)
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+{
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+ struct detect_cycle *new;
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+
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+ new = malloc(sizeof(*new));
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+ if (!new)
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+ return NULL;
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+
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+ new->next = next;
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+ new->data = data;
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+
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+ new->head = head;
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+ new->slow_p = head;
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+ new->fast_p = head;
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+ new->length = 0;
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+ new->power = 2;
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+
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+ return new;
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+}
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+
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+int dc_next(struct detect_cycle *dc, void **next)
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+{
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+
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+ if (dc->length == dc->power) {
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+ dc->length = 0;
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+ dc->power *= 2;
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+ dc->slow_p = dc->fast_p;
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+ }
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+
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+ dc->fast_p = dc->next(dc->fast_p, dc->data);
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+ dc->length++;
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+
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+ if (dc->slow_p == dc->fast_p)
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+ return 1;
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+
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+ *next = dc->fast_p;
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+ return 0;
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+}
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+
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+void dc_find_start(struct detect_cycle *dc, void **first, unsigned long *len)
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+{
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+ void *slow_p, *fast_p;
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+ unsigned long tmp;
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+
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+ slow_p = fast_p = dc->head;
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+ tmp = dc->length;
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+
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+ while (tmp) {
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+ fast_p = dc->next(fast_p, dc->data);
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+ tmp--;
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+ }
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+
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+ while (slow_p != fast_p) {
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+ slow_p = dc->next(slow_p, dc->data);
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+ fast_p = dc->next(fast_p, dc->data);
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+ }
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+
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+ *first = slow_p;
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+ *len = dc->length;
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+}
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diff --git a/makedumpfile-1.7.0/detect_cycle.h b/makedumpfile-1.7.0/detect_cycle.h
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new file mode 100644
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index 0000000000000000000000000000000000000000..2ca75c78b59a98274fc5a98666b1be74f7bbfc2c
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--- /dev/null
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+++ b/makedumpfile-1.7.0/detect_cycle.h
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@@ -0,0 +1,40 @@
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+/*
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+ * detect_cycle.h -- Generic cycle detection using Brent's algorithm
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+ *
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+ * Created by: Philipp Rudo <prudo@redhat.com>
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+ *
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+ * Copyright (c) 2022 Red Hat, Inc. All rights reserved.
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+ *
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+ * This program is free software; you can redistribute it and/or modify
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+ * it under the terms of the GNU General Public License as published by
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+ * the Free Software Foundation; either version 2 of the License, or
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+ * (at your option) any later version.
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+ *
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+ * This program is distributed in the hope that it will be useful,
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+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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+ * GNU General Public License for more details.
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+ */
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+
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+struct detect_cycle;
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+
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+typedef void *(*dc_next_t)(void *prev, void *data);
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+
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+/*
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+ * Initialize cycle detection.
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+ * Returns a pointer to allocated struct detect_cycle. The caller is
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+ * responsible to free the memory after use.
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+ */
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+struct detect_cycle *dc_init(void *head, void *data, dc_next_t next);
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+
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+/*
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+ * Get next entry in the list using dc->next.
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+ * Returns 1 when cycle was detected, 0 otherwise.
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+ */
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+int dc_next(struct detect_cycle *dc, void **next);
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+
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+/*
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+ * Get the start and length of the cycle. Must only be called after cycle was
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+ * detected by dc_next.
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+ */
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+void dc_find_start(struct detect_cycle *dc, void **first, unsigned long *len);
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