On Mon, 8 May 2017 13:06:17 +0200 Richard Weinberger <richard.weinberger@xxxxxxxxx> wrote: > On Mon, May 8, 2017 at 12:49 PM, Pavel Machek <pavel@xxxxxx> wrote: > > Aha, nice, so it looks like ubifs is a step back here. > > > > 'clean marker' is a good idea... empty pages have plenty of space. > > If UBI (not UBIFS) faces an empty block, it also re-erases it. Unfortunately, that's not the case, though UBI can easily be patched to do that (see below). > The EC header is uses as clean marker. That is true. If the EC header has been written to a block, that means this block has been correctly erased. > > > How do you handle the issue during regular write? Always ignore last > > successfully written block? I guess UBIFS can know what was written last, because of the log-based approach + the seqnum stored along with FS nodes, but I'm pretty sure UBIFS does not re-write the last written block in case of an unclean mount. Richard, am I wrong? > > The last page of a block is inspected and allowed to be corrupted. Actually, it's not really about corrupted pages, it's about pages that might become unreadable after a few reads. > > > Do you handle "paired pages" problem on MLC? > > Nope, no MLC support in mainline so far. Richard and I have put a lot of effort to reliably support MLC NANDs in mainline, unfortunately this projects has been paused. You can access the last version of our work here [1] if you're interested (it's clearly not in a shippable state ;-)). [1]https://github.com/bbrezillon/linux-sunxi/commits/bb/4.7/ubi-mlc --->8--- diff --git a/drivers/mtd/ubi/attach.c b/drivers/mtd/ubi/attach.c index 93ceea4f27d5..3d76941c9570 100644 --- a/drivers/mtd/ubi/attach.c +++ b/drivers/mtd/ubi/attach.c @@ -1121,21 +1121,20 @@ static int scan_peb(struct ubi_device *ubi, struct ubi_attach_info *ai, return err; goto adjust_mean_ec; case UBI_IO_FF_BITFLIPS: + case UBI_IO_FF: + /* + * Always erase the block if the EC header is empty, even if + * no bitflips were reported because otherwise we might + * expose ourselves to the 'unstable bits' issue described + * here: + * + * http://www.linux-mtd.infradead.org/doc/ubifs.html#L_unstable_bits + */ err = add_to_list(ai, pnum, UBI_UNKNOWN, UBI_UNKNOWN, ec, 1, &ai->erase); if (err) return err; goto adjust_mean_ec; - case UBI_IO_FF: - if (ec_err || bitflips) - err = add_to_list(ai, pnum, UBI_UNKNOWN, - UBI_UNKNOWN, ec, 1, &ai->erase); - else - err = add_to_list(ai, pnum, UBI_UNKNOWN, - UBI_UNKNOWN, ec, 0, &ai->free); - if (err) - return err; - goto adjust_mean_ec; default: ubi_err(ubi, "'ubi_io_read_vid_hdr()' returned unknown code %d", err);
