kexec-tools: i386 sys interface changes compatibility

On Wed, Dec 14, 2005 at 02:50:52PM -0600, Milton Miller wrote:

[..]
> >>(2) why do you stat the files instead of just trying to open them and
> >>check for ENOENT?
> >>
> >>milton
> >>
> >
> >I wanted to differentiate between two cases. One being sysfs not
> >mounted
> >and other being file not being present (Due to kernel bug or cpu not
> >present), hence used stat(). In case of sysfs not being mounted, we
> >simply exit after giving an error message. In other case we continue
> >to loop through other cpus and ignore cpu, which is not present.
> >
>
> Ok, but try to open the file first.  IF you want to do this diagnostic
> after the open fails, that is ok.  But don't do this check n times (n =
> number of cpus) when the file exists.
>

I have moved the sysfs mounted check in failure condition.

>
> >
> >On Tue, Dec 13, 2005 at 09:36:26AM -0800, Haren Myneni wrote:
> >>Vivek, I believe, we should push this func into arch independent code.
> >>Otherwise, we have to copy it for every platform.
> >>
> >
> >We have reworked the patch and moved this code to architecture
> >independent
> >portion.
> >
>
>
> Only the x86 code has the fallback the old name, not the genric code.
>

Only i386 port of kdump was available when crash_notes was exported
through /sys/kernel/crash_notes. Rest of the architectures see new arch-
independent percpu crash_notes sysfs interface only. Hence thought no
point copying backward compatibility code in generic code.

>
> Also, there are error paths that do not set the address, others that
> zero it.
>

The error paths which do not set address to zero are non return path. They
call die() which inturn calls exit(1) after printing appropriate error
messasge.

> What happens if the base kernel is too old for kexec-panic, where
> neiter file will exist?
>

In that case kexec will fail much earlier. There will be  no reserved
memory area for loading second kernel (crashkernel=X&Y) hence attempt to
load the second kernel will fail and control will not reach this place at
all.

Modifed patch appended.

Thanks
Vivek

o This patch moves per cpu interface to retrieve crash_notes address to
  architecture independent section. (As suggested by Haren)

o For i386, kernels older than 2.6.15-rc1-mm2 used to export crash_notes
  through /sys/kernel/crash_notes. This patch also provides backward
  compatibility with older kernel versions.

o Definition of MAX_NOTE_BYTES moved to architecture independent header
  file as everybody is using same definition.

o Definition of MAX_LINE moved to architecture independent header file.
  Seems to be a better option than defining it in many C files.

Signed-off-by: Maneesh Soni <maneesh@in.ibm.com>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Maneesh Soni <maneesh@in.ibm.com>

1 files changed, 65 insertions, 0 deletions

diff --git a/kexec/crashdump.c b/kexec/crashdump.c
new file mode 100644
index 0000000..9e5bf15
--- /dev/null
+++ b/kexec/crashdump.c
@@ -0,0 +1,65 @@
+/*
+ * crashdump.c: Architecture independent code for crashdump support.
+ *
+ * Created by: Vivek Goyal (vgoyal@in.ibm.com)
+ * Copyright (C) IBM Corporation, 2005. All rights reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation (version 2 of the License).
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <limits.h>
+#include <elf.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include "kexec.h"
+#include "crashdump.h"
+
+/* Returns the physical address of start of crash notes buffer for a cpu. */
+int get_crash_notes_per_cpu(int cpu, uint64_t *addr)
+{
+	char crash_notes[PATH_MAX];
+	char line[MAX_LINE];
+	FILE *fp;
+	struct stat cpu_stat;
+	int count;
+	unsigned long long temp;
+
+	sprintf(crash_notes, "/sys/devices/system/cpu/cpu%d/crash_notes", cpu);
+	fp = fopen(crash_notes, "r");
+	if (!fp) {
+		/* Either sysfs is not mounted or CPU is not present*/
+		if (stat("/sys/devices", &cpu_stat))
+			die("Sysfs is not mounted. Try mounting sysfs\n");
+
+		/* CPU is not physically present.*/
+		*addr = 0;
+		return errno;
+	}
+	if (fgets(line, sizeof(line), fp) != 0) {
+		count = sscanf(line, "%Lx", &temp);
+		if (count != 1)
+			die("Cannot parse %s: %s\n", crash_notes,
+						strerror(errno));
+		*addr = (uint64_t) temp;
+	}
+#if 0
+	printf("crash_notes addr = %Lx\n", *addr);
+#endif
+	return 0;
+}