From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from e35.co.us.ibm.com ([32.97.110.153]) by bombadil.infradead.org with esmtps (Exim 4.68 #1 (Red Hat Linux)) id 1JAPY1-0002Ub-Cj for linux-mtd@lists.infradead.org; Thu, 03 Jan 2008 12:51:52 +0000 Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com [9.17.195.106]) by e35.co.us.ibm.com (8.13.8/8.13.8) with ESMTP id m03CphtQ025562 for ; Thu, 3 Jan 2008 07:51:43 -0500 Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d03relay04.boulder.ibm.com (8.13.8/8.13.8/NCO v8.7) with ESMTP id m03Cphbh111608 for ; Thu, 3 Jan 2008 05:51:43 -0700 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m03CpPko005094 for ; Thu, 3 Jan 2008 05:51:26 -0700 Subject: Re: [PATCH 4/5] UBI: introduce attach ioctls From: Frank Haverkamp To: dedekind@infradead.org In-Reply-To: <1198075329.18962.70.camel@sauron> References: <20071219154137.23264.28116.sendpatchset@golum> <20071219154158.23264.95037.sendpatchset@golum> <200712191517.18166.arnd@arndb.de> <1198075329.18962.70.camel@sauron> Content-Type: multipart/signed; micalg=sha1; protocol="application/x-pkcs7-signature"; boundary="=-M0bF9VGbh0J/hxtXi+uJ" Date: Thu, 03 Jan 2008 13:51:39 +0100 Message-Id: <1199364699.7726.34.camel@august> Mime-Version: 1.0 Cc: Arnd Bergmann , Andreas Arnez , Alexander Schmidt , linux-mtd@lists.infradead.org, Thomas Gleixner , haver@vnet.ibm.com Reply-To: haver@vnet.ibm.com List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --=-M0bF9VGbh0J/hxtXi+uJ Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable Hi Arnd and Artem, On Wed, 2007-12-19 at 16:42 +0200, Artem Bityutskiy wrote: > On Wed, 2007-12-19 at 15:17 +0100, Arnd Bergmann wrote: > > > +struct ubi_attach_req { > > > + int32_t vid_hdr_offset; > > > + int32_t data_offset; > > > }; > >=20 > > Can you explain why you need to pass vid_hdr_offset /and/ data_offset h= ere? > > What is the difference between the two? Data in flash: EC-hdr | VID-hdr | Data -------> VID-hdr-offs -----------------> Data-offset > Can't you autoprobe them if you > > have the device? >=20 > vid_hdr_offset is the offset of the VID header withing an eraseblock. > data_offs is where the data starts. We want to be able to let users > select the VID header offset. > Vs data offset - indeed it is redundant > and might be dropped because UBI may just assume data starts at the next > min. I/O unit after the VID header. Traditionally NAND could only be written only in page-chunks e.g. 2KiB. Thomas Gleixner introduced that subpages could be written too e.g. 512B. In our usage example we decided, that we wanted to have the EC-hdr at offset 0, and the VID-hdr at the end of the last subpage of page 0 in the NAND-erase block. We wanted the data to start at a page boundary so that e.g. JFFS2 can use the pagesize as minimum write size and not the sub-pagesize. Our layout: page 0 | page 1 | ... subpage | ... | subpage | subpage | ... | subpage | ... EC-hdr | ... | VID-hdr | Data Default layout (Artem, correct me if I am wrong): page 0 | page 1 | ... subpage | ... | subpage ... | subpage | ... | subpage | ... EC-hdr | VID-hdr | Data > We can autoprobe the VID header offset, unless the MTD device is empty, > in which case UBI automatically formats it. I do not like auto-probing the VID hdr offset. In my eyes the user should have the flexibility to define where his VID-hdr and data start e.g. like in our case to have influence on if data is starting on subpage- or page-boundaries. I also think that the autoprobe feature would add more complexity to the code. > > The reason I'm asking is that I'd really like to make this a simple > > attribute in sysfs, in the mtd object. The question there is what a > > user would need to store into that attribute. The device is identified > > implicitly already, but this looks like you still need two distint > > integers in order to create an UBI device. I think with our current usage calculating the data offset as next free min-io-offset would work, although the fact that we want to store our data at a page-offset would be done implicitly than. I wonder which layout Thomas Gleixner and Josh Boyer are using? Would it work to calculate the data offset in your case? 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