[PATCH] kdump: Append newline to the last lien of vmcoreinfo note

[PATCH] kdump: Append newline to the last lien of vmcoreinfo note

[Vivek Goyal]

Last line of vmcoreinfo note does not end with \n. Parsing all the lines
in note becomes easier if all lines end with \n instead of trying to special
case the last line.

I know atleast one tool, vmcore-dmesg in kexec-tools tree which made the
assumption that all lines end with \n. I think it is a good idea to
fix it.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
 kernel/kexec.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/kernel/kexec.c
===================================================================
--- linux-2.6.orig/kernel/kexec.c	2012-07-17 19:26:38.844033784 -0400
+++ linux-2.6/kernel/kexec.c	2012-07-17 23:51:33.311701781 -0400
@@ -1424,7 +1424,7 @@ static void update_vmcoreinfo_note(void)
 
 void crash_save_vmcoreinfo(void)
 {
-	vmcoreinfo_append_str("CRASHTIME=%ld", get_seconds());
+	vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
 	update_vmcoreinfo_note();
 }
 

Re: [PATCH] kdump: Append newline to the last lien of vmcoreinfo note

[Andrew Morton]

On Tue, 17 Jul 2012 13:36:55 -0400
Vivek Goyal <vgoyal@redhat.com> wrote:

> Last line of vmcoreinfo note does not end with \n. Parsing all the lines
> in note becomes easier if all lines end with \n instead of trying to special
> case the last line.
> 
> I know atleast one tool, vmcore-dmesg in kexec-tools tree which made the
> assumption that all lines end with \n. I think it is a good idea to
> fix it.
> 
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> ---
>  kernel/kexec.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/kernel/kexec.c
> ===================================================================
> --- linux-2.6.orig/kernel/kexec.c	2012-07-17 19:26:38.844033784 -0400
> +++ linux-2.6/kernel/kexec.c	2012-07-17 23:51:33.311701781 -0400
> @@ -1424,7 +1424,7 @@ static void update_vmcoreinfo_note(void)
>  
>  void crash_save_vmcoreinfo(void)
>  {
> -	vmcoreinfo_append_str("CRASHTIME=%ld", get_seconds());
> +	vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
>  	update_vmcoreinfo_note();
>  }

huh, that was a screwup.  And now we have to make what must be
viewed as a non-back-compatible ABI change.

Ho hum, presumably there isn't a lot of code out there which is
dependent upon a non-newline-terminated CRASHTIME record.

Why did this work at all, anyway?  Is CRASHTIME always the last-emitted
record?

Re: [PATCH] kdump: Append newline to the last lien of vmcoreinfo note

[Vivek Goyal]

On Wed, Jul 18, 2012 at 03:04:39PM -0700, Andrew Morton wrote:
> On Tue, 17 Jul 2012 13:36:55 -0400
> Vivek Goyal <vgoyal@redhat.com> wrote:
> 
> > Last line of vmcoreinfo note does not end with \n. Parsing all the lines
> > in note becomes easier if all lines end with \n instead of trying to special
> > case the last line.
> > 
> > I know atleast one tool, vmcore-dmesg in kexec-tools tree which made the
> > assumption that all lines end with \n. I think it is a good idea to
> > fix it.
> > 
> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > ---
> >  kernel/kexec.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > Index: linux-2.6/kernel/kexec.c
> > ===================================================================
> > --- linux-2.6.orig/kernel/kexec.c	2012-07-17 19:26:38.844033784 -0400
> > +++ linux-2.6/kernel/kexec.c	2012-07-17 23:51:33.311701781 -0400
> > @@ -1424,7 +1424,7 @@ static void update_vmcoreinfo_note(void)
> >  
> >  void crash_save_vmcoreinfo(void)
> >  {
> > -	vmcoreinfo_append_str("CRASHTIME=%ld", get_seconds());
> > +	vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
> >  	update_vmcoreinfo_note();
> >  }
> 
> huh, that was a screwup.  And now we have to make what must be
> viewed as a non-back-compatible ABI change.
> 
> Ho hum, presumably there isn't a lot of code out there which is
> dependent upon a non-newline-terminated CRASHTIME record.

I think so. AFAIK, makedumpfile (vmcore filtering utility) is only
user of CRASHTIME=.

> 
> Why did this work at all, anyway?  Is CRASHTIME always the last-emitted
> record?

Yes, CRASHTIME= is always the last emitted line in vmcoreinfo note.

I had a quick look at makedumpfile code and looks like they read the whole
note, dump it to a file and then do fgets() on the file in a loop. As it is
last line in the file, fgets encounters EOF and reads the CRASHTIME= line
successfully. So even after this change makedumpfile should remain
unaffected. 

CCing makedumpfile maintainer, Atsushi Kumagai.

Thanks
Vivek

Re: [PATCH] kdump: Append newline to the last lien of vmcoreinfo note

[Atsushi Kumagai]

Hello Vivek,

On Thu, 19 Jul 2012 09:49:21 -0400
Vivek Goyal <vgoyal@redhat.com> wrote:

> On Wed, Jul 18, 2012 at 03:04:39PM -0700, Andrew Morton wrote:
> > On Tue, 17 Jul 2012 13:36:55 -0400
> > Vivek Goyal <vgoyal@redhat.com> wrote:
> > 
> > > Last line of vmcoreinfo note does not end with \n. Parsing all the lines
> > > in note becomes easier if all lines end with \n instead of trying to special
> > > case the last line.
> > > 
> > > I know atleast one tool, vmcore-dmesg in kexec-tools tree which made the
> > > assumption that all lines end with \n. I think it is a good idea to
> > > fix it.
> > > 
> > > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > > ---
> > >  kernel/kexec.c |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > Index: linux-2.6/kernel/kexec.c
> > > ===================================================================
> > > --- linux-2.6.orig/kernel/kexec.c	2012-07-17 19:26:38.844033784 -0400
> > > +++ linux-2.6/kernel/kexec.c	2012-07-17 23:51:33.311701781 -0400
> > > @@ -1424,7 +1424,7 @@ static void update_vmcoreinfo_note(void)
> > >  
> > >  void crash_save_vmcoreinfo(void)
> > >  {
> > > -	vmcoreinfo_append_str("CRASHTIME=%ld", get_seconds());
> > > +	vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
> > >  	update_vmcoreinfo_note();
> > >  }
> > 
> > huh, that was a screwup.  And now we have to make what must be
> > viewed as a non-back-compatible ABI change.
> > 
> > Ho hum, presumably there isn't a lot of code out there which is
> > dependent upon a non-newline-terminated CRASHTIME record.
> 
> I think so. AFAIK, makedumpfile (vmcore filtering utility) is only
> user of CRASHTIME=.
> 
> > 
> > Why did this work at all, anyway?  Is CRASHTIME always the last-emitted
> > record?
> 
> Yes, CRASHTIME= is always the last emitted line in vmcoreinfo note.
> 
> I had a quick look at makedumpfile code and looks like they read the whole
> note, dump it to a file and then do fgets() on the file in a loop. As it is
> last line in the file, fgets encounters EOF and reads the CRASHTIME= line
> successfully. So even after this change makedumpfile should remain
> unaffected. 
> 
> CCing makedumpfile maintainer, Atsushi Kumagai.

As you said, makedumpfile reads VMCOREINFO line by line with fgets().
So, it's OK that the end of the last line is whether \n or EOF.

Therefore, this change doesn't affect makedumpfile. 


Thanks
Atsushi Kumagai