[PATCH 6/4] [-mm patch] use the existing offsetof().

[Ken'ichi Ohmichi]

Hi Satyam,

Satyam Sharma wrote:
> > BTW I don't think these macros are such a big win in readability or
> > code clarity anyway. And I noticed that there are still some open
> > calls to vmcoreinfo_append_str() in kexec.c (such as for the OS_RELEASE
> > case) which you haven't macro-ized ... we end up having code that looks
> > like:
> > 
> > 	vmcoreinfo_append_str(...);
> > 	...
> > 
> > 	...
> > 	VMCOREINFO_OFFSET(...);
> > 	...
> > 
> > and it's not even obvious (unless you follow on to the definition of the
> > later macro) that the above two are *exactly* the same. So you could also
> > consider just losing the macros altogether.

I want to use these macros for calls to vmcoreinfo_append_str(), because
the strings included in each macro ("SIZE(XXX)=", "OFFSET(XXX)=", etc.)
are very important. makedumpfile command reads these strings and gets the
debugging information (structure sizes, field offsets, etc.). If losing
these macros and there is a typo like "OFESET(page.mapping)=", the command
cannot run. To prevent this mistake, these macros are very useful.

For more readability, I think it is good that all the calls are changed
to macros having a prefix "VMCOREINFO_" like the attached patch.


Thanks
Ken'ichi Ohmichi 

---
Signed-off-by: Ken'ichi Ohmichi <oomichi at mxs.nes.nec.co.jp>

---
diff -rpuN a/include/linux/kexec.h b/include/linux/kexec.h
--- a/include/linux/kexec.h	2007-09-21 09:28:23.000000000 +0900
+++ b/include/linux/kexec.h	2007-09-21 10:26:24.000000000 +0900
@@ -127,6 +127,10 @@ void vmcoreinfo_append_str(const char *f
 	__attribute__ ((format (printf, 1, 2)));
 unsigned long paddr_vmcoreinfo_note(void);
 
+#define VMCOREINFO_OSRELEASE(name) \
+	vmcoreinfo_append_str("OSRELEASE=%s\n", #name)
+#define VMCOREINFO_PAGESIZE(value) \
+	vmcoreinfo_append_str("PAGESIZE=%ld\n", value)
 #define VMCOREINFO_SYMBOL(name) \
 	vmcoreinfo_append_str("SYMBOL(%s)=%lx\n", #name, (unsigned long)&name)
 #define VMCOREINFO_SIZE(name) \
@@ -134,8 +138,8 @@ unsigned long paddr_vmcoreinfo_note(void
 #define VMCOREINFO_STRUCT_SIZE(name) \
 	vmcoreinfo_append_str("SIZE(%s)=%zu\n", #name, sizeof(struct name))
 #define VMCOREINFO_OFFSET(name, field) \
-	vmcoreinfo_append_str("OFFSET(%s.%s)=%lu\n", #name, #field, \
-			      (unsigned long)&(((struct name *)0)->field))
+	vmcoreinfo_append_str("OFFSET(%s.%s)=%zu\n", #name, #field, \
+			      offsetof(struct name, field))
 #define VMCOREINFO_LENGTH(name, value) \
 	vmcoreinfo_append_str("LENGTH(%s)=%lu\n", #name, (unsigned long)value)
 #define VMCOREINFO_NUMBER(name) \
diff -rpuN a/kernel/kexec.c b/kernel/kexec.c
--- a/kernel/kexec.c	2007-09-21 09:28:22.000000000 +0900
+++ b/kernel/kexec.c	2007-09-21 10:17:56.000000000 +0900
@@ -1195,8 +1195,8 @@ unsigned long __attribute__ ((weak)) pad
 
 static int __init crash_save_vmcoreinfo_init(void)
 {
-	vmcoreinfo_append_str("OSRELEASE=%s\n", init_uts_ns.name.release);
-	vmcoreinfo_append_str("PAGESIZE=%ld\n", PAGE_SIZE);
+	VMCOREINFO_OSRELEASE(init_uts_ns.name.release);
+	VMCOREINFO_PAGESIZE(PAGE_SIZE);
 
 	VMCOREINFO_SYMBOL(init_uts_ns);
 	VMCOREINFO_SYMBOL(node_online_map);
_