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SubjectRe: [PATCH 0/4] coredump: core dump masking support v4
On Wed, 28 Mar 2007 21:37:07 +0900 "Kawai, Hidehiro" <hidehiro.kawai.ez@hitachi.com> wrote:

> > Because other people might (reasonably) wish to omit anonymous memory,
> > or private mappings, or file-backed VMAs, or whatever.
> >
> > So maybe /proc/pid/coredump_omit_anon_shared should become
> > /proc/pid/core_dumpfilter, which is a carefully documented bitmask.
>
> There are people who wish to dump VMAs which are not dumped by default.
> Taking this into account, some bits of core_dumpfilter will be set by
> default. This means users have to be aware of the default bitmask
> when they change the bitmask. Perhaps changing the bitmask requires
> 3 steps:
>
> 1. read the default bitmask
> 2. change bits of the mask
> 3. write it to the proc entry
>
> So I think it is better if we provide /proc/pid/core_flags (default:
> all bits are 0) instead of core_dumpfilter. With this interface,
> users who use only one bit of the bitmask (this will be a common case)
> just have to write 2^n to the proc entry. It takes only one step:
>
> 1. write a value to the proc entry
>
> If we can implement at the same cost, core_flags will be better
> because it is useful for users. What would you think about that?
>

It sounds unnecessarily complex, and unnecessarily different from our
normal expectations of /proc files. And the value we read differs from the
value we wrote... I think having a non-zero default will be fine.

>
> By the way, Robin Holt wrote as follows:
>
> > Can you make this a little more transparent? Having a magic bitmask does
> > not seem like the best way to do stuff. Could you maybe make a core_flags
> > directory with a seperate file for each flag. It could still map to a
> > single field in the mm, but be broken out for the proc filesystem.
>
> Do you think Robin's suggestion is acceptable?

Marginal, I think. This is not likely to be a field which a lot of people
modify a lot of times. Those few people who need to work with this can
afford to look the values up in the documentation while writing their
script.

And it requires a distressingly large amount of code to implement a /proc
file. Perhaps in this situation the code can be shared.

otoh, why is it a /proc thing at all?

unsigned long sys_set_corefile_filter(unsigned long enable_mask);
unsigned long sys_clear_corefile_filter(unsigned long enable_mask);

would be better?
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