I am currently reading a book entitled "Linux device drivers" from O'Reilly.
Thing is that this book imo isn't really a guide on how to write drivers but it instead explains all the apis and their prinicples.
So I tried writing a small driver -which doesn't do anything interesting -with what I read so far.
Thing is:
I don't know which file I can execute cat on or echo to in order to invoke my callback functions
it looks nothing like all the other code snippets I found online
The different pieces of code:
my code (https://paste.ubuntu.com/p/8tVyTJTPBQ/)
creates:
$ls /sys/module/main/
oresize holders initsize initstate notes refcnt sections srcversion taint uevent
no new entry in /dev
code snippet using device_create: https://paste.ubuntu.com/p/cJxjdyXjhX/ source
creates:
$ ls /sys/module/main/
coresize holders initsize initstate notes refcnt sections srcversion taint uevent
$ ls -l /dev/ebbchar
crw------- 1 root root 238, 0 Mai 28 07:52 /dev/ebbchar
code using kobjects: https://paste.ubuntu.com/p/nt3XvZs7vF/ source
creates:
$ls -l /sys/kernel/
drwxr-xr-x 2 root root 0 Dec 17 16:29 etx_sysfs
I can see that my code successfully created a bunch of files under /sys/kernel. Now what is the difference in endgoal between my code and the two other snippets? Should I use device_create/kobjects or maybe none of those? The book I am reading doesn't mention anywhere the functions used by the 2 other pieces of code. So not sure which way I am supposed to follow...
Thanks_xe
device_create() creates a device and registers it with sysfs, and create necessary kobjects.
To create necessary kobjects, kobject-related functions(kobject_init(), kobject_add(), ...) are called in device_create().
If you need to create a device, you should call one of device creation functions like device_create().
Answering your question of how to keep up with latest api- Most api if renamed or updated retain similar name and reside mostly in the same header file so a quick grep on the source or easier is http://elixir.bootlin.com/ and search the source doc for a particular function in the Linux release you are working on. if you cant find the API in that release then go through the header to find the new API as the name will almost be the same for example when you will read the Timer chapter , you will find that setup_timer() has been changed to timer_setup(). and few other changes here and there.
If you feel like you can keep up with the latest discussion by subscribing to the kernel maillist or reading the documentation.
Related
i got the problem that a device isnt booting up into linux.
It just holds on "Starting kernel ...".
To get a better grip on what goes wrong i thought it would be nice to get access to the logs from linux.
I can access the userland from uboot via "ls":
Zynq> ls mmc 0:2
ostree/deploy/poky/deploy/9d325972b955e6584d3fad0a7ff1bf1a8.0/etc
<DIR> 2048 .
<DIR> 1024 ..
<DIR> 1024 modprobe.d
0 motd
<DIR> 1024 xdg
<DIR> 1024 logrotate.d
58 rpcbind.conf
1633 inputrc
828 mke2fs.conf
15 timestamp
10929 login.defs
324 issue
<DIR> 1024 sudoers.d
etc ...
Now im looking for a way to copy files from the userland to another device(remote-pc).
I learned about "tftpput" which is available in uboot.
My problem is that "tftpput" expects a save address and size. But i dont know how to get those information.
tftpput - TFTP put command, for uploading files to a server
Usage:
tftpput Address Size [[hostIPaddr:]filename]
I was not able to find a good documentation on "tftpput". Maybe someone has a link for me or provide me a small "how to" about this?
Thanks in advance
To answer the specific question, you need a tftp server on another machine. Then when you use 'load' to bring a file into memory you will now have that address, $filesize will now be set for you (for the size parameter) and the machine you setup a tftp server on is the final part of the command.
That said, if you only see "Starting kernel" and nothing else, it is quite likely that the linux kernel isn't getting to the point where the rootfs is mounted, userland runs and you're going to see log files. Without more information it's hard to say what you need to do here, but your bootargs are the first place to make sure are correct.
To analyze why the kernel is not booting you could enable the early console.
For ARM 64bit systems the early console is enabled via the kernel command line parameters. U-Boot takes these from the environment variable bootargs.
The arguments for earlycon depend on your board, e.g. for the Odroid C2:
setenv bootargs earlycon=meson,0xc81004c0
For an early console on 32bit ARM system you will have to compile the kernel with appropriate configuration options, e.g. for the Banana Pi:
CONFIG_DEBUG_LL=y
CONFIG_DEBUG_SUNXI_UART0=y
CONFIG_EARLY_PRINTK=y
lets assume that file.txt has 16bytes of size (it is 10 in hex)
First it is necessary load the file into the memory
fatload mmc 1:1 0x40400000 file.txt
Then you can send it to tftp server:
tftpput 0x40400000 10 192.168.7.1:filetxt
Ok so I am having problems with syslog on Raspbian Stretch. I am trying to write to /var/log/blah.log using local0 as my facility. I am using gnu C++ 11 As the application is being written in C++ so I trying to create a logging class.
My /etc/syslog.conf has the following entry
local0.* /var/log/blah.log
... and I have restarted the service and the Pi.
My code to open the log is as follows:
setlogmask(LOG_UPTO(LOG_DEBUG));
openlog(blah, LOG_PERROR | LOG_CONS | LOG_NDELAY, LOG_LOCAL0);
...and my logging code is:
syslog(LOG_INFO | LOG_LOCAL0, fullMessage.c_str());
There is no /var/log/blah.log file created and no log entries written, although the message is written to the console as I am using LOG_CONS.
If I replace LOG_LOCAL0 with LOG_USER I am successfully able write to user.log.
I do want to be able to write to the custom log file because:
a) it is easy to ask a user to look at that file for debugging purposes
b) it should work!!
As I have stated I have looked through the numerous posts on this site and others and still cannot get it top work so posting links to man pages and other articles won't help!
I created a tiny OS for my controller with Linux kernel 2.6.37.6 with the help of BusyBox and tool chain. I am writing a logging module(C program) in it and i want customized logs(customized path for different logs) like in /log/.
I have syslogd in my machine and /etc/syslog.conf supposed to present in my machine but it's not it the place. I created new syslog.conf under /etc but still i can't find my logs in desired place.
But if i run command syslogd -O /log/Controller.log all logs started to redirect to this (specified file). So i want to know where is the configuration file for this syslogd i can't find the configuration file for it.
Is there any way that i can write a module(program) for LOGS without requiring syslog.conf and yes of course traditional printf way. Problem is that for customized paths for log we need to give keyname LOG_LOCAL1 in openlog() as a argument but it's not working
I followed procedure from this examples http://www.codealias.info/technotes/syslog_simple_example
If you are using Busybox's syslogd then there is no support of syslog.conf,all logs are written to /var/log/messages by default.
You can modify code of syslogd in busybox which is located in busybox/sysklogd/syslogd.c for your desire behaviour
You can change code of syslogd like this
static const struct init_globals init_data = {
.logFile = {
.path = "your desire path",
.fd = -1,
},
I have configured a private APT repository (using resources on internet like http://inodes.org/2009/09/14/building-a-private-ppa-on-ubuntu/) and I'm uploading for the first time my package containing the sources of my C++ application.
So reprepro repository is empty.
I use the following command in order to start the build:
sudo reprepro -V -b /srv/reprepro processincoming incoming
Then the build start, a lot of output is genearated and I can see that pbuilder is compiling the project source code and everything is fine. I can even find in the result/ folder debian packages etc...
But the build failed with a POST_BUILD_FAILED because it seems that pbuilder has changed the douane-testing_0.8.1-apt1.debian.tar.gz file and the md5 sum is now different as shown here:
File "pool/main/d/douane-testing/douane-testing_0.8.1-apt1.debian.tar.gz" is already registered with different checksums!
md5 expected: 97257ae2c5790b84ed7bb1b412f1d518, got: df78f88b97cadc10bc0a73bf86442838
sha1 expected: ae93c44593e821696f72bee4d91ce4b6f261e529, got: d6f910ca5707ec92cb71601a4f4c72db0e5f18d9
sha256 expected: c3fac5ed112f89a8ed8d4137b34f173990d8a4b82b6212d1e0ada1cddc869b0e, got: ebdcc9ead44ea0dd99f2dc87decffcc5e3efaee64a8f62f54aec556ac19d579c
size expected: 2334, got: 2344
There have been errors!
I don't understand why it is failing as when I compare the 2 packages (having those md5 sums) the content is strictly the same (I used a diff tool but no differences and no new or removed files).
The only thing I can see is that the archive from pbuild is bigger of 10 Bytes than the orginal one I have uploaded:
On my development machine, the file with the md5 97257ae2c5790b84ed7bb1b412f1d518 :
-rw-r--r-- 1 zedtux zedtux 2334 Feb 3 23:38 douane-testing_0.8.1-apt1.debian.tar.gz
On my server, the file with the md5 df78f88b97cadc10bc0a73bf86442838 :
-rw-r--r-- 1 root root 2344 Feb 5 00:58 douane-testing_0.8.1-apt1.debian.tar.gz
I have pbuild version 0.213 on my server.
What could be the reason of this behavior and how can I fix it ?
Edit
I'm suspecting an issue with the GPG key which looks missing and then files aren't signed so md5sum is different.
During the build process I have the following lines:
I: Extracting source
gpgv: Signature made Wed Feb 5 22:04:37 2014 UTC using RSA key ID 9474CF36
gpgv: Can't check signature: public key not found
dpkg-source: warning: failed to verify signature on ./douane-testing_0.8.1-apt1.dsc
Edit 2
I have tried to find the command to create manually the .debian.tar.gz file.
The best I've found is the following:
tar cv debian | gzip --no-name --rsyncable -9 > douane-testing_0.8.1-apt1.debian.tar.gz
I don't get the same result than dpkg-source but I tried the same command on my server (I should at least have the same size) but it's not matching...
Could it be that Debian and Ubuntu aren't compressing the same way ?
Finally after some evenings of research I found the solution on launchpad.net !
Found the solution. By default pbuilder calls dpkg-buildpackage like so:
DEBBUILDOPTS="$DEBBUILDOPTS -rfakeroot"
dpkg-buildpackage -us -uc $DEBBUILDOPTS
That causes dpkg-buildpackage to rebuild the diff.gz and .dsc files. Add a -b in there, and it won't. It also means the resulting .changes file will only reference the .deb file. Which is what you want, I think.
The easy solution is to add a line to your .pbuilderrc:
DEBBUILDOPTS="-b"
My previous answer is alright but is not complete.
Then I had the issue that reprepro complains about the source tarball (.orig.tar.xz).
But it was normal as I wasn't doing the packages correctly.
I have written a bash script which I'm executing in VM for each Ubuntu series.
This script was always doing everything from scratch, and was using dh_make --createorig argument and here is the issue.
The correct way is to generate once (for example on Ubuntu precise) and then re-use the .orig.tar.xz file and no more use the --createorig argument of dh_make.
I hope this could help someone :-)
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