From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.nokia.com ([192.100.122.233] helo=mgw-mx06.nokia.com) by bombadil.infradead.org with esmtps (Exim 4.69 #1 (Red Hat Linux)) id 1NIJb8-0003O1-BN for linux-mtd@lists.infradead.org; Wed, 09 Dec 2009 10:16:46 +0000 Subject: Re: UBIFS read-only rootfs needs 1 or more eraseblocks to mount From: Artem Bityutskiy To: Darwin Rambo In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Date: Wed, 09 Dec 2009 12:16:28 +0200 Message-Id: <1260353788.19669.1265.camel@localhost> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Cc: "linux-mtd@lists.infradead.org" Reply-To: dedekind1@gmail.com List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 2009-12-08 at 16:09 -0800, Darwin Rambo wrote: > On a read-only UBIFS rootfs, why do you need at least 1 eraseblock? > There is nothing to replace since nothing is ever written to this > partition on the fly and a block that goes bad cannot be recovered > anyways? > > UBI error: ubi_eba_init_scan: no enough physical eraseblocks (0, need > 1) > UBI error: ubi_init: cannot attach mtd6 > UBI error: ubi_init: UBI error: cannot initialize UBI, error -28 This is UBI error, not UBIFS. UBI does not really have a notion of read-only UBI device, so it always reserves some amount of eraseblocks. There is a compile-time option about amount of eraseblocks to reserve, in percent. You can make it 0%, then UBI will not reserve anything. Probably it will not work out of the box (I never tried that), and you'll need to do some small investigation / fixing. > Note that adding room for a single bad block PEB allows the mount to > work, and you get a warning like this: > "UBI warning: ubi_eba_init_scan: cannot reserve enough PEBs for bad > PEB handling, reserved 0, need 19" This is again UBI warning, not UBIFS. > It looks like the normal read/write code is reserving/requiring blocks > that the read-only mode doesn't actually use? R/O stuff is on UBIFS level, you get warning at UBI level, and UBI does assumes everything is R/W. > All this is probably just a future suggestion to support read-only > mode a little bit better with less block wastage. Ok, you might as well just come up with a patch or patches! -- Best Regards, Artem Bityutskiy (Артём Битюцкий)