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create multiple SquashFS partitions

Hello

I'm working on embedded platform (Broadcom's bcm5358u processor with MIPS core), where I need extra partitions for the purpose of further upgrade procedure. The filesystem used is SquashFS, so I modified 'struct mtd_partition' accordingly, which is passed to MTD related code, and I ended up with this (dmesg snippet):

Creating 7 MTD partitions on "sflash":

0x00000000-0x00020000 : "boot" 0x00020000-0x00600000 : "bank1os" 0x00188820-0x00600000 : "bank1fs" 0x00600000-0x00be0000 : "bank2os" 0x00788820-0x00be0000 : "bank2fs" 0x00be0000-0x00ff0000 : "app" 0x00ff0000-0x01000000 : "nvram"

#cat /proc/partitions major minor #blocks name

31 0 128 mtdblock0 31 1 6016 mtdblock1 31 2 4573 mtdblock2 31 3 6016 mtdblock3 31 4 4445 mtdblock4 31 5 4160 mtdblock5 31 6 64 mtdblock6

#cat /proc/mtd dev: size erasesize name mtd0: 00020000 00010000 "boot" mtd1: 005e0000 00010000 "bank1os" mtd2: 004777e0 00010000 "bank1fs" mtd3: 005e0000 00010000 "bank2os" mtd4: 004577e0 00010000 "bank2fs" mtd5: 00410000 00010000 "app" mtd6: 00010000 00010000 "nvram"

Now I want to be able to mount /dev/mtdblock4 as a temporary storage during system upgrade, but I can't do this, because it appears that this partition mtdblock4 doesn't have any FS installed. The kernel image and FS are integrated in one image, which is flashed down the /dev/mtdblock2 (which is supplied as root_fs to kernel).

I see only one solution: create a empty squashFS image, write it on /dev/mtdblock4 and may be it will work as I want (?). Is there a way to, like, format the partition on the fly, whenever the kernel boots, or it violates the MTD concepts?

Thanks.

--
Mark
Reply to
Mark
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Hi Mark.

Note that squashfs is read-only, so you won't be able to write anything to it. I suspect you'll want to use something like jffs. Or if you have lots of RAM to spare, you could use a tmpfs filesystem rather than needing flash at all.

I haven't tried it with squashfs, but with some filesystems you can just initialize the entire flash partition with zeros (mfill followed by fis create if you are using RedBoot). If that works for your chosen fs, you should be able to fill the /dev/mtdblock4 with zeros post-boot, prior to issuing the mount command.

Regards, Steve

Reply to
steve_schefter

Thank you for the response, Steve. I do actually need this partition as a permanent storage, but I though (perhaps mistakenly?) that JFFS is normally used on NAND type flash, which I don't have?

--
Mark
Reply to
Mark

Hi Mark.

JFFS (actually JFFS2 these days) and YAFFS work with NAND and NOR flash. That is, any flash which is under the MTD driver. You just can't use those for flash types which are not directly connected and therefore are not under MTD, such as SD/MMC/USB flash.

Steve

Reply to
steve_schefter

To perhaps clarify this somewhat: The main difference between NAND and NOR flash from a user's viewpoint is that NOR flash can be used just like any other memory area being part of the physical memory map of a system for read accesses while NAND flash chips are actually 'block devices' and not random-access memory. But this difference is virtualized away at the mtd layer and anything which uses that just invokes the read- and write-methods of the virtual MTD device.

Reply to
Rainer Weikusat

Steve, so it is possible to have different FS (for example, squash and jffs) on the same flash device? Is this maintained by the same MTD driver ?

--
Mark
Reply to
Mark

Correct me if I'm wrong: so MTD subsystem knows nothing about filesystems itself, and only deals with logical separation between low-level flash device complexities from the higher-level data organization.

--
Mark
Reply to
Mark

Hi Mark.

on

Yes, you can mix the file system types.

The MTD driver has no involvement in what file system is used. That's under the control of fs/jffs2 and the like. MTD operates at a lower level. In fact, there might not even be a file system in some of the partitions, such as where you kernel image is stored.

Steve

Reply to
steve_schefter

Hi Mark,

Also you can do XIP(of your application) to save some amount of RAM and you can use the saved RAM space as temperory storage for your application

abhayadev s

Reply to
abhayadev s.

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