From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from top.free-electrons.com ([176.31.233.9] helo=mail.free-electrons.com) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1WAdqZ-0003uP-H7 for linux-mtd@lists.infradead.org; Tue, 04 Feb 2014 11:07:20 +0000 Date: Tue, 4 Feb 2014 08:06:44 -0300 From: Ezequiel Garcia To: Willy Tarreau , Artem Bityutskiy Subject: Re: [PATCH 1/1] ubi: Introduce block devices for UBI volumes Message-ID: <20140204110643.GA2414@localhost> References: <1391027881-8354-1-git-send-email-ezequiel.garcia@free-electrons.com> <1391027881-8354-2-git-send-email-ezequiel.garcia@free-electrons.com> <20140131170636.GJ31190@1wt.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20140131170636.GJ31190@1wt.eu> Cc: Thomas Petazzoni , Mike Frysinger , Michael Opdenacker , linux-mtd@lists.infradead.org, Tim Bird , Piergiorgio Beruto , Brian Norris , David Woodhouse List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, Jan 31, 2014 at 06:06:37PM +0100, Willy Tarreau wrote: > On Wed, Jan 29, 2014 at 05:38:01PM -0300, Ezequiel Garcia wrote: > > Block device emulation on top of ubi volumes with cached read/write support. > > Both the cached access and the write support are selectable at compile time. > > > > Given UBI takes care of wear leveling and bad block management it's possible > > to add a thin layer to enable block device access to UBI volumes. > > This allows to use a block-oriented filesystem on a flash device. > > > > In a similar fashion to mtdblock, a 1-LEB size cache has been > > implemented. However, very memory-constrained systems can choose to > > disable the cache and save the 1-LEB byte allocation. > > > > If write support is enabled, the flash device will be written when the cache > > is flushed. The following events trigger this: > > * block device release (detach) > > * different than cached leb is accessed > > * io-barrier is received through a REQ_FLUSH request > > > > Despite this efforts, it's very important to remember that regular > > block-oriented filesystems have no care at all about wear leveling; > > they will access the block device randomly, only caring for performance. > > Therefore, write support should be selected only for development and > > with extreme caution. > > > > The cache is 1-LEB bytes, vmalloced at open() and freed at release(); > > in addition, each block device has a workqueue associated. > > > > Block devices are created upon user request through new ioctls: > > UBI_IOCVOLATTBLK to attach and UBI_IOCVOLDETBLK to detach. > > Also, a new UBI module parameter is added 'ubi.block'. This parameter is > > needed in order to attach a block device on boot-up time, allowing to > > mount the rootfs on a ubiblock device. > > For instance, you could have these kernel parameters: > > > > ubi.mtd=5 ubi.block=0,0 root=/dev/ubiblock0_0 > > > > Or, if you compile ubi as a module: > > > > $ modprobe ubi mtd=/dev/mtd5 block=/dev/ubi0_0 > > > > Cc: Artem Bityutskiy > > Cc: David Woodhouse > > Cc: Brian Norris > > Cc: Michael Opdenacker > > Cc: Tim Bird > > Cc: Thomas Petazzoni > > Cc: Mike Frysinger > > Cc: Piergiorgio Beruto > > Cc: Willy Tarreau > > Signed-off-by: Ezequiel Garcia > > Works pretty well here on 3.14-git. I've also tested write support > with success. I'm booting from a squashfs installed on top of it. > I find that the combination of squashfs + ubiblock is really good > for a rootfs. It's fast, space-efficient in terms of RAM and NAND, > and made reliable by the ubi layer. > > Concerning the question about the usage of write support, I find it > useful to perform rootfs upgrades from Linux. > > Feel free to add : > > Tested-By: Willy Tarreau > Thanks Willy! Artem: If at all possible, I'd like to avoid stalling, so feel free to comment on anything... -- Ezequiel García, Free Electrons Embedded Linux, Kernel and Android Engineering http://free-electrons.com