Exercises for NTB walk through "Einstieg in die Linux Treiberentwicklung".
| Command | Description |
|---|---|
pwd |
Returns the current path |
uname -r |
Returns the version of the Kernel headers |
insmod <module>.ko |
Attach module to Kernel |
rmmod <module>.ko |
Remove module from Kernel |
dmesg |
Prints the Kernel log |
tail |
Returns the last 10 lines of a file (usage i.e. ```dmesg |
cat |
Calls sequential 'open', 'read' and 'close' |
scp <file> <user>@<target>:<desitnation> |
Copy a file over ssh to the target |
- Driver can be interrupted at any time. Make sure, the usage of shared resources doesn't lead to any troubles.
- The Kernel owns just a small Stack, use it with care. Don't use recursive methods.
- Floating point operations are not possible.
- Use double underlined "__" function calls with care. They are low level calls.
- No access to the common used C libraries. However, the Kernel provides its own library containing the most important functions.
#include <linux/fs.h> is needed by register_chrdev_region, alloc_chrdev_region and unregister_chrdev_region.
#include <linux/kdev_t.h> is needed by MKDEV(...,...), MINOR(...) and MAJOR(...).
Formated Kernel print message:
printk(KERN_INFO "Assigned major and minor numbers are: %u, %u\n", MAJOR(mDevice), MINOR(mDevice));
Close the message string using \n otherwise, the message is throw until a \n was committed.
| Loglevel | Description |
|---|---|
| KERN_EMERG | An emergency condition; the system is probably dead |
| KERN_ALERT | A problem that requires immediate attention |
| KERN_CRIT | A critical condition |
| KERN_ERR | An error |
| KERN_WARNING | A warning |
| KERN_NOTICE | A normal, but perhaps noteworthy, condition |
| KERN_INFO | An informational message |
| KERN_DEBUG | A debug message typically superfluous |
C error codes: /usr/include/asm-generic/errno-base.h
Formats:
| Data type | Format specifier |
|---|---|
| int | %d or %x |
| int | %u or %x |
| long | %ld or %lx |
| unsigned long | %lu or %lx |
| long long | %lld or %llx |
| unsigned long long | %llu or %llx |
| size_t | %zu or %zx |
| ssize_t | %zd or %zx |
| s32 | %d or %x |
| u32 | %u or %x |
| s64 | %lld or %llx |
| u64 | %llu or %llx |
Pointers:
%pF versatile_init+0x0/0x110
%pf versatile_init
%pS versatile_init+0x0/0x110
%pSR versatile_init+0x9/0x110 (with __builtin_extract_return_addr() translation)
%ps versatile_init
%pB prev_fn_of_versatile_init+0x88/0x88
Source: http://www.makelinux.net/books/lkd2/ch18lev1sec3
An udev created device-file belongs to root. To make it accessible by user, the device-file rights can be changed manually using chmod.
Alternatively and more elegant is to define a rule in /etc/udev/rules.d/. The rule filename has two parts: Order-Number and Description text, separated by dash.
The content of the file looks like this:
KERNEL=="testDevice", OWNDER="root", GROUP"root", "MODE="0666"
Make will make files from other files. This can make troubles if you have a file named i.e. <> and in your makefile also used the label <>. In this case, make will use the file instead of handle <> as a label. Using the .PHONY command will tell make the name isn't associated with a file: .PHONY clean.
https://www.kernel.org/doc/htmldocs/
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