makedumpfile: a feature question about filtering

[HAGIO KAZUHITO(萩尾 一仁)]

-----Original Message-----
> On 09/14/2020 04:15 PM, HAGIO KAZUHITO(萩尾　一仁) wrote:
> > -----Original Message-----
> >> On 09/11/2020 04:53 PM, HAGIO KAZUHITO(萩尾　一仁) wrote:
> >>> Hi Pingfan,
> >>>
> >>> -----Original Message-----
> >>>> Hello,
> >>>>
> >>>> There is an appeal which only wants to save some user page including env
> >>>> and args pages, and discards the other user space pages.
> >>>
> >>> I understand that it's helpful to get them even with -d 31 for crash's
> >>> "ps -a" option..
> >>>
> >>>>
> >>>> To achieve this feature, mm_struct's members "arg_start, arg_end,
> >>>> env_start, env_end;" should be accessed. So we need to export mm_struct
> >>>> and init_mm through vmcore.
> >>>
> >>> How many offsets/sizes will be required to walk all tasks?
> >> At present, I think only the info "arg_start, arg_end, env_start,
> >> env_end" in mm_struct are required.
> >
> > ah what I wanted to ask mainly was the number of the offsets/sizes used to
> > walk through all (user) tasks in a system, because makedumpfile cannot get
> > to a task's arg_start only with OFFSET(mm_struct.arg_start).  Is it easy
> > enough to do it only with several vmcoreinfo entries?
> Yes, it is. Iterating over tasks requires to expose
> OFFSET(mm_struct.mmlist, and &init_mm. Then for each mm_struct, we need
> an access to "arg_start, arg_end, env_start,env_end"

Hmm, but a Fedora 32 machine has an empty init_mm.mmlist.
(because of no used swap?)

crash> p init_mm.mmlist
$1 = {
  next = 0xffffffff826ee200 <init_mm+160>, 
  prev = 0xffffffff826ee200 <init_mm+160>
}
crash> swap
SWAP_INFO_STRUCT    TYPE       SIZE       USED     PCT  PRI  FILENAME
ffff8badb5385a00  PARTITION  4153340k      0k       0%   -2  /dev/dm-1

I might be still missing something.

Thanks,
Kazu