Messages in this thread | | | Date | Fri, 19 Oct 2018 15:02:10 +0300 | From | Vitaly Chikunov <> | Subject | Re: dm: add secdel target |
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On Thu, Oct 18, 2018 at 04:01:25PM -0400, Mike Snitzer wrote: > On Sun, Oct 14 2018 at 7:24am -0400, > Vitaly Chikunov <vt@altlinux.org> wrote: > > > Report to the upper level ability to discard, and translate arriving > > discards to the writes of random or zero data to the underlying level. > > > > Signed-off-by: Vitaly Chikunov <vt@altlinux.org> > > --- > > This target is the same as the linear target except that is reports ability to > > discard to the upper level and translates arriving discards into sector > > overwrites with random (or zero) data. > > There is a fair amount of code duplication between dm-linear.c and this > new target. > > Something needs to give, ideally you'd factor out methods that are > shared by both targets, but those methods must _not_ introduce overhead > to dm-linear.
I see three possible solutions: - integrate 'secdel' into dm-linear; - export functions like linear_dax_copy_to_iter and fill them into secdel's `struct target_type`; - call methods of linear's `struct target_type` from secdel's one.
> Could be that dm-linear methods just get called by the wrapper > dm-sec-erase target (more on the "dm-sec-erase" name below).
> > diff --git a/drivers/md/dm-secdel.c b/drivers/md/dm-secdel.c > > new file mode 100644 > > index 000000000000..9aeaf3f243c0 > > --- /dev/null > > +++ b/drivers/md/dm-secdel.c > ... > > + if (mode == SECDEL_MODE_RAND) { > > + page = alloc_page(gfp_mask); > > + if (!page) { > > + DMERR("%s %lu[%lu]: no memory to allocate page for random data", > > + __func__, sector, nr_sects); > > + /* will fallback to zero filling */ > > In general, performing memory allocations to service IO is something all > DM core and DM targets must work to avoid. This smells bad. > > ...
Yes, but we need to create and write random data, so I don't see other solution. In zero overwriting mode page is not allocated. And it's fall back to zero overwriting if page allocation fails for random data.
> Mike
I will address these and other your concerns in v2.
Thanks!
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