From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lunge.queued.net ([173.255.254.236]) by canuck.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1REiX6-0005jM-Ss for linux-mtd@lists.infradead.org; Fri, 14 Oct 2011 14:14:45 +0000 Date: Fri, 14 Oct 2011 07:14:16 -0700 From: Andres Salomon To: dedekind1@gmail.com Subject: Re: [PATCH] jffs2: allow disabling of compression schemes at runtime Message-ID: <20111014071416.5278051d@debxo> In-Reply-To: <1318582244.12351.73.camel@sauron> References: <20111003191624.7efd3dce@queued.net> <1318582244.12351.73.camel@sauron> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: linux-mtd@lists.infradead.org, David Woodhouse , linux-kernel@vger.kernel.org List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, 14 Oct 2011 11:50:37 +0300 Artem Bityutskiy wrote: > On Mon, 2011-10-03 at 19:16 -0700, Andres Salomon wrote: > > Currently jffs2 has compile-time constants (and .config options) > > regarding whether or not the various compression/decompression > > drivers are built in and enabled. This is fine for embedded > > systems, but it clashes with distribution kernels. Distro kernels > > tend to turn on everything; this causes OpenFirmware to fall > > over, as it only supports ZLIB decompression. Booting a kernel > > that has LZO compression enabled, writing to the boot partition, > > and then rebooting causes OFW to fail to read the kernel from > > the filesystem. This is because LZO compression has priority > > when writing new data to jffs2, if LZO is enabled. > > > > To get around that, this patch adds jffs2 module params for each > > compressor type that isn't decompression-only. That means I can run > > a kernel that has support for LZO and ZLIB decompression (allowing > > me to read LZO data off of the root partition), while disabling > > LZO compression writes (jffs2.disable_lzo=1) so that the boot > > partition stays compatible with OFW. > > > > Signed-off-by: Andres Salomon > > You should use mount options instead. Invent nice mount options to > configure compression strategy of JFFS2. I thought about it, but currently jffs2 doesn't support parsing mount options. It seemed like a lot of extra code for such an obscure feature, on a filesystem that's merely in maintenance mode (I don't know if anyone else has run into the same issue that I have). However, I can do that if desired. > > Or you can simply implement the same option as UBIFS has: compr=xxx. > Yep. > See Documentation/filesystems/ubifs.txt > > With this option you set the default compressor which is use when > writing, and on reading all decompression are supported, seems like > exactly what you want. You can also look how it is implemented in > UBIFS for reference. >