I bought mini 2440 2-3 years back. In that purchase CD the kernel image and root filesystem are provided separately and instructed to port separately. Why it is so? Doesn't the root filesystem(yaffs2 type) contain the kernel image in its filesystem hierarchy before building yaffs2 filesystem image? Please reply for my doubt!
The sequence of start-up events are: bootloader, kernel and in the final stages of the kernel start-up is the mounting of the root file system. " The Linux kernel itself doesn't dictate any filesystem structure, but user space programs do expect to find files ..... " Building Embedded Linux Systems: Yaghmour,Masters,Ben-Yossef and Gerum.
Yes that sequence was while mounting when the board is ready to boot contained with all files. But my doubt is while flashing the files in the board why we have to flash kernel and then rootfs image. according to filesystem hierarchy standard the / directory or /boot directory contains kernel image. Then we can flash the rootfs image itself which contains kernel image in it right? why we are flashing kernel image at one time and rootfs image at another time for mini2440 with the bootloader provided?
Where do you find the kernel image in the mini2440 distro? It has been years since I used that image. I know about vmlinux in Ubuntu etc http://en.wikipedia.org/wiki/Vmlinux but not any mini2440 distro, that I know of
Hi davef, If you look at the download manual document for Linux dowloaded from this page http://www.friendlyarm.net/downloads it says that through DNW tool we have to use option 'k' for downloading kernel image and 'y' for downloading yaffs2 root filesystem image. U can check with that..
Sorry, I see I didn't ask the question correctly. Where do you find the kernel image inside the root filesystem image?
according to filesystem hierarchy standard the / directory or /boot directory contains kernel image. Re-reading carefully I now understand the point you are trying to make. I was not aware of this "standard".
Can anybody please clarify my above doubt correctly?
A guess: possibly the non bootable static linked kernel, vmlinux, for debugging/symbol table that is stored in the rootfs???
> Why it is so? Just simple: if the kernel is part of the root filesystem the bootloader must support the filesystem to be able to extract and run the kernel from it. How many filesystems should a bootloader support? And what about new filesystems (UBIFS versus JFFS2) or filesystem improvements and bug fixes? If you handle both components separately you can use whatever filesystem you like and your kernel supports. And the bootloader and its capability doesn't matter.
Hi Juergen, Then my questions are 1:doesnot the kernel image reside in / directory in mini2440 board ? 2: or if it resides in / directory how the offset is calculated to exactly flash the kernel image in the / directory because we are giving physical address as arguments in bootloader and not the directory information? Please reply!
Ayyappan, what do you mean with "/ directory"? In our world the '/' is the root of the currently mounted and used file system in a running system. This is only a "view" into a filesystem, independent from the media this filesystem is stored (can be a RAM disk, a JFFS2 on a flash, an EXT4 on an SD card and so on). To "2:" I believe you are talking about a partitioned flash device, don't you? The offset into the NAND can't be calculated. Its defined and you must know the offsets.
So with your reply my understanding is "any directory in filesystem is not fixed to a physical address they are only a relative location with respect to the root of the currently mounted and used filesystem in a running system". Am I right? Please correct if not. And I am talking about partitioned flash device only and as you said offset into the NAND can't be calculated and its defined and I must know the offsets, where can I fix that address for any new board? Is there any logic behind that? And one more question if my bootloader has the capability for extracting the kernel from my filesystem type, is it ok to place kernel image in / directory or / boot directory and then build rootfs image and flash the rootfs image containing the kernel image within itself at the same time? Please reply!
Your first question: hard to answer. In a Linux system you can mount filesystems on your needs and elsewhere. Lets think about two partitions in your NAND: one for the root filesystem and one for the home directories. Each of these independent filesystems has its own '/'. It depends on the way you mount them at runtime which '/' is the root from the Linux point of view. root filesystem data filesystem /. /. |-bin/ |-user_a |-etc/ |-user_b |-home/ |-user_c . . . . . . At runtime: /. <- root filesystem's root and system's root |-bin/ |-etc/ |-home// <--- data filesystem's root . |-user_a . |-user_b . |-user_c So: about what '/' you are talking about? > [...9 I must know the offsets, where can I fix that address Don't know, because I don't know what you are doing. > Is there any logic behind that? A NAND memory has a special internal data layout. You must ensure your partitions honor this layout. Otherwise it will not work. So the restrictions where the offsets of the partitions are located depend on the NAND type you are using (and must also honor bad blocks and so on). Your last question: no idea, because I don't know what you are doing.
1) first question was about root filesystem's root and system's root. 2) "I must know the offsets, where can I fix that address" What I come to ask is how to decide physical address of kernel image and rootfs image to be resided while flashing? A generic answer or the point of reference to study will be good for me ,atleast how it was decided in mini2440 is needed. 3) Is there any logic behind that? 2nd question answer will be useful for this question. 4) last question is about the following. I have built uboot bootloader image for mini2440 and I am trying to build rootfs image of jffs2 type for learning purpose. So if uboot.bin supports jffs2 type can I have kernel image within rootfs image and flash kernel image along with rootfs image at the same time(if memory is also available for both )as you said "the bootloader must support the filesystem to be able to extract and run the kernel from it." Please reply!
for --> 4) last question is about the following. I planned to place kernel image in / directory in root filesystem hierarchy and then build rootfs image in jffs2 type.