On 2013/11/19 18:56:21, kexec <kexec-bounces at lists.infradead.org> 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 <kumagai-atsushi@xxxxxxxxxxxxxxxxx> Date: Wed, 20 Nov 2013 14:10:19 +0900 Subject: [PATCH] Fall back to read() when mmap() fails. Signed-off-by: Atsushi Kumagai <kumagai-atsushi at 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); } } else { if (lseek(info->fd_memory, offset, SEEK_SET) == failed) { -- 1.8.0.2
