From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Petermaier Date: Wed, 12 Mar 2014 18:19:00 +0100 Subject: [U-Boot] [PATCH] Add support for offset of a filesystem within a block-device In-Reply-To: <20140312160823.GS16805@bill-the-cat> References: <1394112635-21016-1-git-send-email-oe5hpm@oevsv.at> <20140312160823.GS16805@bill-the-cat> Message-ID: <53209704.303@petermaier.org> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de On 2014-03-12 17:08, Tom Rini wrote: > On Thu, Mar 06, 2014 at 02:30:35PM +0100, Hannes Petermaier wrote: > >> For clear separation of user's (OS) filesystem to U-Boot and other's >> stuff it is now possible to give the filesystem a specific offset and a >> specific size. >> For full consistency OS storage driver also has to support this and >> has to use same offset and size. >> >> Following new parameters has been added to the block_dev_desc_t >> structure: >> - lba_offset : offset in blocks from which fs is reading/writing >> - lba_fs : size in blocks of fs >> >> This two parameters are filled from the underlaying device-driver. >> As default they are initialized for giving whole size of block-device >> to the filesystem. >> >> In case of mmc-driver a function for modifiying drive geometry is >> called 'board_mmc_geometry', this function is implemented as >> '__weak', so it can be replaced by a board-specific function, which >> can setup suitable offset and size for the filesystem. >> This function is responsible for giving reasonable values, e.g. >> lba_offset+lba_fs must not exceed available blocks of the device. >> >> Only MMC Driver and FATFS are modified to support this. >> >> Signed-off-by: Hannes Petermaier > Sorry if I'm being dense here, but what is the usecase exactly? When we > don't have a partition table of some sort? > Hi Tom, I try to explain the use case with my application as example: I have an eMMC flash with 4GB space. On my target OS vxWorks is running, which has as filesystem a simple DOS-FAT. I would like to give an offset to the filesystem due to two reasons: a) U-Boot with its environment should / can not remain within the DOSFS (it should not be accessible by the user/OS). Also U-Boot must be at least with the MLO "in front" of the flash since i am booting from the eMMC flash. b) i want limit the user-accessible space to the flash to about 512MB. There are, for my unterstanding, two ways to achieve this: a) give no offset for the "blockdevice" at all and have a partition table at the bottom of flash (ROM code searches in my case (am3352) at several places for a bootable code, so this method would be suitable for booting) - i don't know how it is on other processors, the rest would be magic of the following partioning software (OS) - but many os (vxworks for example) cannot have specific start-cylinder for the first partition, we would have to rewrite the partitioner. Making a change within the partitioning section at the OS is therefore a bit critical, not at least because changes there affects all other block devices too. So plan b) looked best for my opinion: Give a specific offset/size to the 'blockdevice' within raw-flash. We have to adapt only the specific blockdevice driver to detect/have a specific offset/size and rest of OS don't need to know about this special situation. We don't use the space laying before the offset within the OS at all (clear separation). Within U-Boot we can use the whole flash in "raw-mode" and use "FAT" with the beginning of specified offset. With the offset i also can control how much space is left for the OS and its filesystem. Is my explanation clear ? please feel free to ask me more. Whats your opinion about this ? best regards, Hannes