On 11/20/13 at 05:27am, Atsushi Kumagai wrote:
> On 2013/11/19 18:56:21, kexec wrote:
> > (2013/11/18 9:51), Atsushi Kumagai wrote:
> > > (2013/11/15 23:26), Vivek Goyal wrote:
> > >> On Fri, Nov 15, 2013 at 06:41:52PM +0900, HATAYAMA Daisuke wrote:
> > >>
> > >> [..]
> > Given the fact that hpa does not like fixing it in kernel. We are
> > left with option of fixing it in following places.
> >
> > - Drop partial pages in kexec-tools
> > - Drop partial pages in makeudmpfile.
> > - Read partial pages using read() interface in makedumpfile
> > - Modify /proc/vmcore to copy partial pages in second kernel's memory.
> >
> > It is not clear to me that partial pages are really useful. So I
> > want to avoid modifying /proc/vmcore to deal with partial pages and
> > increase complexity.
> >
> > So fixing makedumpfile (either option2 or option 3) seems least
> > risky to me. In fact I would say let us keep it simple and truncate
> > partial pages in makedumpfile to keep it simple. And look at option
> > 3 once we have a strong use case for partial pages.
> >
> > What do you think?
> >
> > >>>
> > >>> As you say, it's not clear that partial pages are really useful, but
> > >>> on the other hand, it seems to me not clear that they are really
> > >>> useless.
> > >>> I think we should get them as long as we have access to them.
> > >>>
> > >>> It seems best to me the option 3). Switching between read and mmap
> > >>> would be not so complex and also it's by far flexible in
> > >>> makedumpfile than in kernel.
> > >>
> > >> Ok, I am fine with option 3. It is more complicated option but safe
> > >> option.
> > >
> > > It sounds reasonable also to me.
> > >
> > >> Is there any chance that you could look into fixing this. I have no
> > >> experience writing code for makedumpfile.
> > >
> > > I'll send a patch to fix this soon.
> > >
> >
> > Thanks.
> >
> > BTW, now the following patch has been applied on top of makedumpfile in
> > kexec-tools package on fedora in order to avoid the issue.
> >
> > https://lists.fedoraproject.org/pipermail/kexec/2013-November/000254.html
> >
> > I remember prototype version of mmap patch implemented a kind of --no-mmap
> > option and we could use it to disable mmap() use and use read() instead, I
> > think which is useful when we face this kind of issue.
>
> How about this fail back structure instead of such an extra option ?
>
> Thanks
> Atsushi Kumagai
>
> From: Atsushi Kumagai
> Date: Wed, 20 Nov 2013 14:10:19 +0900
> Subject: [PATCH] Fall back to read() when mmap() fails.
>
> Signed-off-by: Atsushi Kumagai
> ---
> makedumpfile.c | 10 +-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/makedumpfile.c b/makedumpfile.c
> index ca03440..f583602 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -324,7 +324,15 @@ read_from_vmcore(off_t offset, void *bufptr, unsigned
> long size)
> if (!read_with_mmap(offset, bufptr, size)) {
> ERRMSG("Can't read the dump memory(%s) with mmap().\n",
> info->name_memory);
> - return FALSE;
> +
> + ERRMSG("This kernel might have some problems about
> mmap().\n");
> + ERRMSG("read() will be used instead of mmap() from
> now.\n");
> +
> + /*
> + * Fall back to read().
> + */
> + info->flag_usemmap = FALSE;
> + read_from_vmcore(offset, bufptr, size);
Hi, Atsushi
I've got such a workstation too. And I confirm this patch works for me.
However, I have a question:
Why not switch to mmap() back after read()?
Thanks
WANG Chao
> }
> } else {
> if (lseek(info->fd_memory, offset, SEEK_SET) == failed) {
> --
> 1.8.0.2
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