On 11/25/13 at 08:09am, Atsushi Kumagai wrote:
> Hello WANG,
>
> On 2013/11/21 16:15:22, kexec <kexec-boun...@lists.infradead.org> wrote:
> > > How about this fail back structure instead of such an extra option ?
> > >
> > > Thanks
> > > Atsushi Kumagai
> > >
> > > From: Atsushi Kumagai <kumagai-atsu...@mxc.nes.nec.co.jp>
> > > Date: Wed, 20 Nov 2013 14:10:19 +0900
> > > Subject: [PATCH] Fall back to read() when mmap() fails.
> > >
> > > Signed-off-by: Atsushi Kumagai <kumagai-atsu...@mxc.nes.nec.co.jp>
> > > ---
> > > 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.
>
> Thanks for your testing !
>
> > However, I have a question:
> > Why not switch to mmap() back after read()?
>
> I made this patch as a general safety net, not only for the partial page
> issue.
> When facing unknown issues related mmap(), the kernel may have some bugs
> and mmap() can fail for every pages. In the worst case, most all mmap()
> will fail and try read() with error messages after every fail, but this
> patch will prevent the chattering of the switch and so many error messages.
Thanks for you explanation. I agree with you. Since mmap() is error
prone after first mmap failure, use read() instead as a fail safe makes
much sense to me.
WANG Chao
>
>
> Thanks
> Atsushi Kumagai
>
> > Thanks
> > WANG Chao
> >
> > > }
> > > } else {
> > > if (lseek(info->fd_memory, offset, SEEK_SET) == failed) {
> > > --
> > > 1.8.0.2
> >
> > _______________________________________________
> > kexec mailing list
> > ke...@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> >
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