From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <1522748411.3673.12.camel@mhfsdcap03> Subject: Re: [PATCH] mtd: Add sysfs attribute for mtd OOB available size From: xiaolei li To: Boris Brezillon CC: , , , Date: Tue, 3 Apr 2018 17:40:11 +0800 In-Reply-To: <20180403104354.03895246@bbrezillon> References: <1522657210-56833-1-git-send-email-xiaolei.li@mediatek.com> <1522657210-56833-2-git-send-email-xiaolei.li@mediatek.com> <20180402141505.33051c14@bbrezillon> <1522723618.3504.7.camel@mhfsdcap03> <20180403104354.03895246@bbrezillon> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit MIME-Version: 1.0 List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 2018-04-03 at 10:43 +0200, Boris Brezillon wrote: > On Tue, 3 Apr 2018 10:46:58 +0800 > xiaolei li wrote: > > > Hello Boris, > > > > On Mon, 2018-04-02 at 14:15 +0200, Boris Brezillon wrote: > > > Hi Xiaolei, > > > > > > On Mon, 2 Apr 2018 16:20:10 +0800 > > > Xiaolei Li wrote: > > > > > > > Expose mtd OOB available size by sysfs file. Then users can get available > > > > OOB size by accessing /sys/class/mtd/mtdX/oobavail. > > > > > > May I ask why you need to expose that? I'm not against exposing new > > > things through sysfs, but since this is part of the ABI, I'd like to be > > > sure we actually need it. > > > > > That is user-space can write OOB data through ioctl MEMWRITE now. > > If OOB operation mode is MTD_OPS_AUTO_OOB, user should know how many > > OOB available bytes it can use. But I didn't find a way to get it. (If > > there is already a method, please kindly let me know, thanks.) > > Nope. We have the ECCGETLAYOUT ioctl, but it's not reliable because of > the MTD_MAX_OOBFREE_ENTRIES limitation. > > > > > One problem I know is to do Jffs2 type flash erase using MTD user-space > > tool flash_erase. flash_erase tool will program "cleanmarker" into OOB > > free area, but it can not get OOB available size. > > That's a good reason to expose this property indeed. Do you plan to fix > mtd-utils to use the sysfs value when it's available? Also, do we need > to expose the ECC/free layout as done with the > ECCGETLAYOUT/MEMGETOOBSEL ioctls? > Yes. I plan to fix mtd-utils problem if this change is accepted. struct nand_oobinfo and struct nand_ecclayout_user in mtd-abi.h are obsoleted, and user can not get oob layout by ioctl method now. sysfs seems a method to fetch oob layout. But I don't know which user-space case will use oob layout now. Maybe expose them in the future if they are really needed? Thanks, Xiaolei