I'm trying to understand where uboot stores the environment variables in emmc. I have the following set in the uboot config file -
CONFIG_ENV_IS_NOWHERE=y
CONFIG_ENV_IS_IN_MMC=y
CONFIG_SYS_MMC_ENV_DEV=2
CONFIG_SYS_MMC_ENV_PART=0
CONFIG_ENV_SIZE=0x4000
CONFIG_ENV_OFFSET=0x400000
CONFIG_ENV_SECT_SIZE=0x10000
uboot is able to save the env variables in emmc and I can read them from Linux. Variables set from Linux are also readable in uboot. I fail to understand which partition has the environment variables?
Output lsblk from Linux -
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
mtdblock0 31:0 0 16M 0 disk
mmcblk2 179:0 0 7.3G 0 disk
|-mmcblk2p1 179:1 0 83.2M 0 part /run/media/mmcblk2p1
|-mmcblk2p2 179:2 0 1.7G 0 part /
|-mmcblk2p3 179:3 0 83.2M 0 part /run/media/mmcblk2p3
|-mmcblk2p4 179:4 0 1K 0 part
|-mmcblk2p5 179:5 0 1.7G 0 part /run/media/mmcblk2p5
`-mmcblk2p6 179:6 0 1G 0 part /run/media/mmcblk2p6
mmcblk2boot0 179:32 0 4M 1 disk
mmcblk2boot1 179:64 0 4M 1 disk
mmcblk2boot0 is where uboot is located which is 4MB in size, considering the environment is saved at an offset of 0x400000 in mmcblk2 device, it should be located just after mmcblk2boot0 which points to the parition mmcblk2boot1, but if I dump the strings "strings /dev/mmcblk2boot1", I get nothing.
I have provided a file /etc/fw_config which is used by fw_printenv and fw_saveenv, this file contains "/dev/mmcblk2 0x400000 0x10000". All the settings point to the fact that uboot environment is located at an offset of 0x400000 in mmcblk2 device. Any pointers on which partition listed in output of lsblk holds the uboot environment variables..?
Thanks,
Vinay
The confusing thing here is that CONFIG_SYS_MMC_ENV_PART does not refer to sofware partitions, such as /dev/mmcblk2p1 that you see under Linux, but rather hardware partitions such as /dev/mmcblk2 (partition 0) or /dev/mmcblk2boot0 (partition 1).
As the title says I have a problem with my custom kernel module. My goal is to retrieve the root mount point of a given path. Just like using df:
df "/tmp/some_dir/some_file"
vvvvvvvv out vvvvvvvv
Filesystem 1K-blocks Used Available Use% Mounted on <---
tmpfs 8125932 120 8125812 1% /tmp <----
I was trying to achieve it with path struct by using both mnt and dentry fields but when I printed mnt_root or superblock root it always returned '/' so not associated mounting point.
Maybe I'm just digging in the wrong place. I don't know if path/dentry/etc... are suitable structures for these operations (I'm beginning my adventure with kernel modules and probably I'm overkilling it :D)
Kernel version: 5.6.2
Thanks in advice!
I have managed to reach my goal!
It turns out that there is follow_up function in namei.c which does exactly what I needed.
i am working on BF548 EZKIT LITE, i had done tftp booting in it. Kernel and jffs2 file system loaded successfully and got the root prompt.
But now i need to use SD card for booting, I had made ext2 partition into sd card and copy u-boot.ldr(boot loader) in it, but when try to load this file after inserting SD card into board i had got an error like
tranfering data failed
** ext4fs_devread read error - block
Failed to mount ext2 filesystem...
** Unrecognized filesystem type **
search on net but could not find anything , add log for detail which shows SD card is detected.
bfin> mmcinfo
Device: Blackfin SDH
Manufacturer ID: 3
OEM: 5344
Name: SD02G
Tran Speed: 25000000
Rd Block Len: 512
SD version 2.0
High Capacity: No
Capacity: 1.8 GiB
Bus Width: 4-bit
bfin>
bfin> ext2load mmc 0 0x1000000 u-boot.ldr
tranfering data failed
** ext4fs_devread read error - block
Failed to mount ext2 filesystem...
** Unrecognized filesystem type **
bfin>
I had tried different sd card also but still got the same problem, Any one have clue about this? Please share.
U-boot version= 2014.07.
Linux kernel = 4.5.4
I am using Buildroot for making board support package.
Thank in advance....
Ah, so your problem is:
bfin> ext2load mmc 0 0x1000000 u-boot.ldr
and this should be:
bfin> ext4load mmc 0:1 0x1000000 u-boot.ldr
as you need to specify both the MMC device (0) and the partition on the device (1 as you made 1 partition on the SD card and formatted that). Just saying 0 causes it to try and read the whole device as where the filesystem is which fails when it runs into the partition table. And you need to use 'ext4load' (or just load, if you have the generic commands enabled) as well since you've got ext3/ext4 most likely and not just ext2.
Fatfs is a small library written in C ansi that lets us manage a file system on a storage device. I am planning on using it in an embedded project in order to store several files on an SD Card.
Therefore I try to make some tests on a USB flash drive, having downloaded the provided examples. I can mount my usb flash drive.
After having compiled the sources without the option FS_READONLY, I have initialized my drive and mounted it as well. But I cannot create a directory!
Here is the commands I entered within the prompt example provided here: http://elm-chan.org/fsw/ff/ffsample.zip
>fi 2 (force initialisation)
rc=0 FR_OK
>di 2 (mount the drive)
rc=0
Sector size = 512
Number of sectors = 30282525
>fj (switch the current drive to '2', which is actually my usb stick)
rc=0 FR_OK
>fk foo (Attempt to create a dir called 'foo')
rc=1 FR_DISK_ERR
Taking a look at the documentation, we're informed that FR_DISK_ERR refers to an hardware error.
Is my flash drive badly formated? Did I miss something else during the initialisation?
I would like to know which entry under /dev a file is in. For example, if /dev/sdc1 is mounted under /media/disk, and I ask for /media/disk/foo.txt, I would like to get /dev/sdc as response.
Using stat system call on that file I will get its partition major and minor numbers (8 and 33, for sdc1). Now I need to get the "root" device (sdc) or its major/minor from that. Is there any syscall or library function I could use to link a partition to its main device? Or even better, to get that device directly from the file?
brw-rw---- 1 root floppy 8, 32 2011-04-01 20:00 /dev/sdc
brw-rw---- 1 root floppy 8, 33 2011-04-01 20:00 /dev/sdc1
Thanks in advance!
The quick and dirty version: df $file | awk 'NR == 2 {print $1}'.
Programmatically... well, there's a reason I started with the quick and dirty version. There's no portable way to programmatically get the list of mounted filesystems. (getmntent() gets fstab entries, which is not the same thing.) Moreover, you can't even parse the output of mount(8) reliably; on different Unixes, the mountpoint may be the first or the last item. The most portable way to do this ends up being... parsing df output (And even that is iffy, as you noticed with the partition number.). So you're right back to the quick and dirty shell solution anyway, unless you want to traverse /dev and look for block devices with matching major(st_rdev) (major() being from sys/types.h).
If you restrict this to Linux, you can use /proc/mounts to get the list of mounted filesystems. Other specific Unixes can similarly be optimized: for example, on OS X and I think FreeBSD, you can use sysctl() on the vfs tree to get mountpoints. At worst you can find and use the appropriate header file to decipher whatever the mount table file is (and yes, even that varies: on Solaris it's /etc/mnttab, on many other systems it's /etc/mtab, some systems put it in /var/run instead of /etc, and on many Linuxes it's either nonexistent or a symlink to /proc/mounts). And its format is different on pretty much every Unix-like OS.
The information you want exists in sysfs which exposes the linux device tree. This models the relationships between the devices on the system and since you are trying to determine a parent disk device from a partition, this is the place to look. I don't know if there are any hard and fast rules you can rely on to stop your code breaking with future versions of the kernel, but the kernel developers do try to maintain sysfs as a stable interface.
If you look at /sys/dev/block/<major>:<minor>, you'll see it is a symlink with the tail components being block/<disk-device-name>/<partition-device-name>. If you were to perform a readlink(2) system call on that, you could parse the link destination to get the disk device name. In shell (since it's easier to express this way, but doing it in C will be pretty easy):
$ echo $(basename $(dirname $(readlink /sys/dev/block/8:33)))
sdc
Alternatively, you could take advantage of the nesting of partition directories in the disk directories (again in shell, but from C, its an open(2), read(2), and close(2)):
$ cat /sys/dev/block/8:33/../dev
8:32
That assumes your starting major:minor is actually for a partition, not some other sort of non-nested device.
What you looking for is impossible - there is no 1:1 connection between a block device file and the partition it is describing.
Consider:
You can create multiple block device files with different names (but the same major and minor numbers) and they are indistinguishable (N:1)
You can use a block device file as an argument to mount to mount a partition and then delete the block device file leaving the partition mounted. (0:1)
So there is no way to do what you want except in a few specific and narrow cases.
Major number will tell you which device it is: 3 - IDE on 1st controller, 22 - IDE on 2nd controller and 8 for SCSI.
Minor number will tell you partition number and - for IDE devices - if it's primary or secondary drive. This calculation is different for IDE and SCSI.
For IDE it is: x*64 + p, x is drive number on the controller (0 or 1) and p is partition
For SCSI it is: y*16 + p, where y is drive number and p is partition
Not a syscall, but:
df -h /path/to/my/file
From https://unix.stackexchange.com/questions/128471/determine-what-device-a-directory-is-located-on
So you could look at df's source code and see what it does.
I realize this post is old, but this question was the 2nd result in my search and no one has mentioned df -h