Mount ubi file system

An example of a video on Debian Jessie of mounting an empty ubi volume on an mtd device. Important note: Sometimes it is impossible to mount device to the folder, because its size is too small. As shown in the example, you need to allocate a partition with a large amount of memory. The first obvious reason is that ubiformat preserves erase counters, so you do not lose your wear-leveling information when flashing new images.

Consider an example. In fewer words, ubiformat makes sure that every NAND page is written once and only once after the erasure. The mkfs. Then you can use it to mount your root. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Learn more. Using squashfs on top of ubi as root file system Ask Question. Asked 3 years, 6 months ago. Active 3 years ago. Viewed 5k times. I flashed the ubi image to mtd19 system and modified my kernel parameters to contain this: ubi. How can I force the kernel to mount it with squashfs instead of ubifs? Improve this question. Well, this does not sound as a big issue. However, compression becomes an issue for free space reporting when compression is combined with write-back.

Namely, UBIFS cannot know how well the cached dirty data would compress, and the only way to find this out is to actually compress it. See below. Suppose there are X bytes of dirty file data in the page cache. They will be flushed to the flash media later, but they are in RAM so far. For example, this may lead to the following situations. But once the data has reached the flash media, they took considerably less flash space.

Consider the following numbers:. But real-life data are often compressible, so data node sizes vary, and the amount of wasted space at the ends of eraseblocks varies from 0 to UBIFS is doing some job to put small nodes like directory entries to the ends of LEBs to lessen the amount of wasted space, but it is not ideal and UBIFS still may waste unnecessarily large chunks of flash space at the ends of eraseblocks.

When reporting free space, UBIFS does not know which kind of data are going to be written to the flash media, and in which sequence. Thus, it assumes the maximum possible wastage of bytes per LEB.

This calculation is too pessimistic for most real-life situations and the average real-life wastage is considerably less than bytes per LEB. However, UBIFS reports the absolute minimum amount of free space user-space applications may count on. Dirty space is the flash space occupied by UBIFS nodes which were invalidated because they were changed or removed.

For example, if the contents of a file is re-written, than corresponding data nodes are invalidated and new data nodes are written to the flash media.

The invalidated nodes comprise dirty space. There are other mechanisms how dirty space appears as well. Please, refer the JFFS2 design document for more information. This produces some amount of free space at the end of the reserved LEB. The process continues until a full empty LEB is produced. Consider a situation when GC picks eraseblocks with less than min. The reason why the last min. Indeed, otherwise an unclean reboot would result in lost data. Anyway, what matters is that UBIFS cannot always reclaim dirty space if the amount of it is less than min.

When UBIFS reports free space to the users, it treats dirty space as available for new data, because after garbage-collection dirty space becomes free space. So it again uses pessimistic calculations. In practice this means that a file system which is close to be full has less accurate free space reporting comparing to a less full file system, because this file system presumably has more dirty space.

Note, to fix this issue, UBIFS would need to run GC in statfs , which would turn as much dirty space as possible into free space, which would result in more precise free space reporting. However, this would make statfs very slow. The index takes some flash space. The FS data in the journal is not indexed, which means that on-flash index does not refer it.

The journal becomes indexed as the result of the commit operation. UBIFS maintains precise accounting of the index size. This means, it does not know whether how much will the index size change after the journal data references will be included into the on-flash index.

This means that file system synchronization the makes free space prediction mistake lower. It is worth noting that this is not a fundamental thing. And the effect of the index size uncertainty should be low. Read the JFFS2 design document.

Remember, the document in general is old and out-of-date. However, the superblock location idea may be used to create new scalable UBI2 layer. The slides were prepared in OpenOffice. The slides contain animation, so you have to watch them in "slide show" mode use F5 key. And if you do not have any possibility to get OpenOffice, here is a pdf version , but it is very ugly because it does not store the animation and draws all animation steps at once.

However, it might be rather difficult for newbies, so we recommend to start with the JFFS3 design document. The code has a great deal of comments, so we recommend to look there if you need all the details. FTL stands for "Flash Translation Layer" and it is software which emulates a block device on top of flash hardware.

At early days FTL ran on the host computer. However, nowadays FTL is usually firmware, and it is run by the controller which is built into the storage device. Well, the interfaces are different and they are defined by different specifications, e. But all of them provide block-based access to the device. By block-based access we mean that whole device is represented as an linear array of usually byte blocks. Each block may be read or written. Linux has an abstraction of a block device.

For example hard drives are block devices. So the idea is that the same software may be used with FTL devices. Although most flashes on the commodity hardware have FTL, there are systems which have bare flashes and do not use FTL. Those are mostly various handheld devices and embedded systems. Raw flash devices are very different to block devices. They have different work model, they have tighter constraints and more issues than block devices. In case of FTL devices these constraints and issues are hidden, but in case of raw flash the software has to deal with them.

Please refer to this table for some more details about the difference between block devices and raw flashes. UBIFS file system has been designed for raw flash. It doesn't work with block devices and it assumes the raw flash device model. In other words, it assumes the device has eraseblocks, which may be written to, read from, or erased.

UBIFS takes care of writing all data out-of-place, doing garbage-collection and so on. All these things are not normally needed for block devices. Very often people ask questions like "why would one need to use raw flash and why not just use eMMC, or something like this? Create a free Team What is Teams? Learn more. Asked 3 years, 10 months ago. Active 3 years, 10 months ago. Viewed 7k times. How can I change a single file from that ubi image?

Improve this question. It seems no difference between ubifs images and images of other fs: unpack image or mount-loop exists image, make some changes and rebuild finally image. I found this link and hope this will be helpful for you - slatedroid.