Re: [Crash-utility] [PATCH v2 5/5] diskdump: Warn on incomplete dumps

-----Original Message----- > On Fri, Jul 09, 2021 at 06:39:44AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote: > > -----Original Message----- > > > On Mon, Jun 21, 2021 at 06:02:51AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote: > > > > -----Original Message----- > > > > > + > > > > > + if (read_pd(dd->dfd, offset, &pd)) { > > > > > + /* > > > > > + * Truncated page descriptor at most > > > > > + * references full page. > > > > > + */ > > > > > + expected_size += block_size; > > > > > + goto next; > > > > > + } > > > > > + > > > > > + if (pd.offset == 0) { > > > > > + if (!first_empty_pd) > > > > > + first_empty_pd = page_idx; > > > > > + /* > > > > > + * Incomplete pages at most use the > > > > > + * whole page. > > > > > + */ > > > > > + expected_size += block_size; > > > > > + } else if (!pd.flags) { > > > > > + /* > > > > > + * Zero page has no compression flags. > > > > > + */ > > > > > > > > Non-compressed page also has no compression flags. > > > > > > > > So something like (pd.offset == dd->data_offset) is needed to determine > > > > whether the page is zero page? although it's not exact without excluding > > > > zero pages. > > > > > > > > > > Hi Kazu, > > > > > > Yes, you're right. Thanks for spotting it. > > > > > > I've added a code path for a case when zero pages are not it's excluded. > > > It's a no brainer. However, I've got some issues figuring out whether a > > > page descriptor references zero page when we start to differentiate > > > zero/non-zero uncompressed pages and calculate expected size accordingly. > > > > > > dd->data_offset points to the beginning of page descriptors and it > > > doesn't help to find zero page: > > > > > > data_offset -> pd for pfn 0 > > > pd for pfn 1 > > > ... > > > pd for pfn N > > > ... <-some gap ??? > > > zero page > > > pfn 0 > > > > Oh, you're right, I misread something. > > > > There should be no gap between pd for pfn N and zero page, but anyway > > we cannot get the number of pds in advance without counting the bitmap.. > > > > I don't know may be some parts of bitmap weren't flushed either. I'll > investigate that further why "valid_pages * descriptor size" is not > equal to offset from data_offset to zero page on an incomplete dump. ugh, sorry, bitmap also can be incomplete in cyclic mode. In that case, page_is_dumpable() cannot be used to estimate the size in the first place, maybe all we can do is to get total_valid_pages..

Thanks, Kazu