svn commit: r316938 - head/sbin/savecore

[Rodney W. Grimes]

> On Fri, Apr 14, 2017 at 01:49:51PM -0600, Alan Somers wrote:
> > On Fri, Apr 14, 2017 at 1:41 PM, Ngie Cooper <ngie at freebsd.org> wrote:
> > > Author: ngie
> > > Date: Fri Apr 14 19:41:48 2017
> > > New Revision: 316938
> > > URL: https://svnweb.freebsd.org/changeset/base/316938
> > >
> > > Log:
> > >   savecore: fix space calculation with respect to `minfree` in check_space(..)
> > >
> > >   - Use strtoll(3) instead of atoi(3), because atoi(3) limits the
> > >     representable data to INT_MAX. Check the values received from
> > >     strtoll(3), trimming trailing whitespace off the end to maintain
> > >     POLA.
> > >   - Use `KiB` instead of `kB` when describing free space, total space,
> > >     etc. I am now fully aware of `KiB` being the IEC standard for 1024
> > >     bytes and `kB` being the IEC standard for 1000 bytes.
> > >   - Store available number of KiB in `available` so it can be more
> > >     easily queried and compared to ensure that there are enough KiB to
> > >     store the dump image on disk.
> > >   - Print out the reserved space on disk, per `minfree`, so end-users
> > >     can troubleshoot why check_space(..) is reporting that there isn't
> > >     enough free space.
> > >
> > >   MFC after:    7 weeks
> > >   Reviewed by:  Anton Rang <rang at acm.com> (earlier diff), cem (earlier diff)
> > >   Tested with:  positive/negative cases (see review); make tinderbox
> > >   Sponsored by: Dell EMC Isilon
> > >   Differential Revision:        D10379
> > 
> > The free space calculation is still uselessly conservative, because it
> > doesn't account for the fact that core dumps will always be either
> > spare or compressed.  The result is that savecore will frequently
> > refuse to save corefiles even when there's plenty of space.  I
> > proposed removing the space check altogether in
> > https://reviews.freebsd.org/D2587.  However, I agreed to wait until
> > after the compressed core dump feature was merged, because then mostly
> > accurate space checks will be possible.  AFAIK the compressed core
> > dump feature still hasn't been finished.
> 
> I had held off on it for a while because it was going to conflict with
> the work to add encrypted dump support, which of course has finished.
> 
> The patch to add compression support is here and should largely still
> work:
> https://people.freebsd.org/~markj/patches/core-compression/20141110-kern_dump.diff
> 
> I've been hesitant about pushing it forward:
> - The dump_write* APIs need some simplification after the addition of
>   encrypted dump support and support for dumping to 4Kn drives.
> - I'm not sure how encryption should compose with compression. It seems
>   intuitively obvious that we should compress before encrypting if the
>   compression is to be of any use, but I don't know enough to know
>   whether the compression might somehow compromise the effectiveness of
>   the encryption.
> 
> If anyone has some insight on the second of these two points, I'd
> appreciate hearing it.

I have a large amount of reworking and modulization of the dump code
incuding intergration of your (markj) compressed dumps.  Layer isnt
implemented but is in the plan.  I should not of held off on the net
dump code as it got smashed by encrypted dumps, then again by
the libif'ing for all the Intel drives that had been netdump modified.

Basically now starting over :-(

Minidump is an lkm for me, and main dump is almost an lkm for me too.
-- 
Rod Grimes                                                 rgrimes at freebsd.org