- With CMake
ggm@gAN515-52:~/Documents/tsmotter/lkd (master)$ rm -rf build && cmake -S . -B build -D m_target=character-hello
...
ggm@gAN515-52:~/Documents/tsmotter/lkd (master)$ cmake --build build --parallel `nproc`
...- Without CMake
ggm@gAN515-52:~/Documents/tsmotter/lkd (master)$ make
...
ggm@gAN515-52:~/Documents/tsmotter/lkd (master)$ make clean- During building, I had the following problem:
ggm@gAN515-52:~/Documents/tsmotter/lkd $ make
make -C /lib/modules/6.5.0-28-generic/build M=/home/ggm/Documents/tsmotter/lkd modules
make[1]: Entering directory '/usr/src/linux-headers-6.5.0-28-generic'
warning: the compiler differs from the one used to build the kernel
The kernel was built by: x86_64-linux-gnu-gcc-12 (Ubuntu 12.3.0-1ubuntu1~22.04) 12.3.0
You are using:
CC [M] /home/ggm/Documents/tsmotter/lkd/hello.o
/bin/sh: 1: gcc-12: not found
make[3]: *** [scripts/Makefile.build:251: /home/ggm/Documents/tsmotter/lkd/hello.o] Error 127
make[2]: *** [/usr/src/linux-headers-6.5.0-28-generic/Makefile:2039: /home/ggm/Documents/tsmotter/lkd] Error 2
make[1]: *** [Makefile:234: __sub-make] Error 2
make[1]: Leaving directory '/usr/src/linux-headers-6.5.0-28-generic'
make: *** [Makefile:4: all] Error 2ggm@gAN515-52:~/Documents/tsmotter/lkd $ which gcc
/usr/bin/gcc
ggm@gAN515-52:~/Documents/tsmotter/lkd $ ls -al /usr/bin/gcc
lrwxrwxrwx 1 root root 6 ago 5 2021 /usr/bin/gcc -> gcc-11
ggm@gAN515-52:~/Documents/tsmotter/lkd $ sudo apt install --reinstall gcc-12
...
ggm@gAN515-52:~/Documents/tsmotter/lkd $ sudo ln -s -f /usr/bin/gcc-12 /usr/bin/gcc
ggm@gAN515-52:~/Documents/tsmotter/lkd $ ls -al /usr/bin/gcc
lrwxrwxrwx 1 root root 15 abr 28 10:55 /usr/bin/gcc -> /usr/bin/gcc-12- Build works now...
ggm@gAN515-52:~/Documents/tsmotter/lkd $ make
CC is equal to: cc
make -C /lib/modules/6.5.0-28-generic/build M=/home/ggm/Documents/tsmotter/lkd modules
make[1]: Entering directory '/usr/src/linux-headers-6.5.0-28-generic'
warning: the compiler differs from the one used to build the kernel
The kernel was built by: x86_64-linux-gnu-gcc-12 (Ubuntu 12.3.0-1ubuntu1~22.04) 12.3.0
You are using: gcc-12 (Ubuntu 12.3.0-1ubuntu1~22.04) 12.3.0
CC is equal to: gcc-12
CC [M] /home/ggm/Documents/tsmotter/lkd/hello.o
CC is equal to: gcc-12
MODPOST /home/ggm/Documents/tsmotter/lkd/Module.symvers
CC [M] /home/ggm/Documents/tsmotter/lkd/hello.mod.o
LD [M] /home/ggm/Documents/tsmotter/lkd/hello.ko
BTF [M] /home/ggm/Documents/tsmotter/lkd/hello.ko
Skipping BTF generation for /home/ggm/Documents/tsmotter/lkd/hello.ko due to unavailability of vmlinux
make[1]: Leaving directory '/usr/src/linux-headers-6.5.0-28-generic'-
The
.kofile created is in fact the kernel object file that can be loaded into the kernel -
Load the module and see it's output in the kernel dmesg:
ggm@gAN515-52:~/Documents/tsmotter/lkd $ sudo insmod hello.ko
ggm@gAN515-52:~/Documents/tsmotter/lkd $ sudo dmesg | grep world
[52854.539596] Hello world!- List the current modules and see the hello module:
ggm@gAN515-52:~/Documents/tsmotter/lkd $ lsmod | grep hello
Module Size Used by
hello 12288 0- Remove the module and see it's output in the kernel dmesg:
ggm@gAN515-52:~/Documents/tsmotter/lkd $ sudo rmmod hello
ggm@gAN515-52:~/Documents/tsmotter/lkd $ sudo dmesg | grep world
[52854.539596] Hello world!
[53017.225366] Goodbye world!- References to commands:
ggm@gAN515-52:~/Documents/tsmotter/lkd $ tldr insmod
insmod
Dynamically load modules into the Linux Kernel.
More information: https://manned.org/insmod.
- Insert a kernel module into the Linux kernel:
insmod path/to/module.ko
ggm@gAN515-52:~/Documents/tsmotter/lkd $ tldr rmmod
rmmod
Remove modules from the Linux kernel.
More information: https://manned.org/rmmod.
- Remove a module from the kernel:
sudo rmmod module_name
- Remove a module from the kernel and display verbose information:
sudo rmmod --verbose module_name
- Remove a module from the kernel and send errors to syslog instead of `stderr`:
sudo rmmod --syslog module_name
ggm@gAN515-52:~/Documents/tsmotter/lkd $ tldr lsmod
lsmod
Shows the status of Linux kernel modules.
See also `modprobe`, which loads kernel modules.
More information: https://manned.org/lsmod.
- List all currently loaded kernel modules:
lsmod-
Created the file
character-hello.c -
Edited the Makefile to
obj-m += character-hello.o
ggm@gAN515-52:~/Documents/tsmotter/lkd $ make
...
ggm@gAN515-52:~/Documents/tsmotter/lkd $ sudo insmod character-hello.ko
ggm@gAN515-52:~/Documents/tsmotter/lkd $ lsmod | grep hello
character_hello 12288 0
ggm@gAN515-52:~/Documents/tsmotter/lkd $ sudo mknod /dev/mydev 98 0
ggm@gAN515-52:~/Documents/tsmotter/lkd $ ls -al /dev | grep 98
crw-r--r-- 1 root root 98, 0 abr 28 11:56 mydev
ggm@gAN515-52:~/Documents/tsmotter/lkd $ sudo su
root@gAN515-52:/home/ggm/Documents/tsmotter/lkd# echo "foo" > /dev/mydev
root@gAN515-52:/home/ggm/Documents/tsmotter/lkd# cat /dev/mydev
foo
foo
foo
foo
^C
root@gAN515-52:/home/ggm/Documents/tsmotter/lkd#
exit
ggm@gAN515-52:~/Documents/tsmotter/lkd $ sudo rmmod character_hello- In another terminal:
ggm@gAN515-52:~/Documents/tsmotter $ sudo dmesg -w
[56748.437235] [Hello.ko] init OK
[56788.334621] [Hello.ko] open OK
[56788.334704] [Hello.ko] write OK
[56788.334733] [Hello.ko] release OK
[56813.806724] [Hello.ko] open OK
[56813.806786] [Hello.ko] read OK
[56813.806811] [Hello.ko] read OK
[56813.806826] [Hello.ko] read OK
[56813.929183] [Hello.ko] release OK
[56890.458021] [Hello.ko] exit OK-
struct filerepresents an open file instance (a handle) -
struct inodeare more related to paths and attributes-
Short for "index node"
-
The exact structure and content of an inode can vary depending on the specific file system implementation, but it typically contains metadata about the file or directory, such as its size, ownership, permissions, timestamps, and pointers to the data blocks where the file's actual content is stored on disk.
-
-
If more than one instance to
fopenis called on the same file, it'll happen to exist multiple instances ofstruct filecoexisting but only one instance ofstruct inode -
There are
struct inode_operationslike get_link, permission, create, link, unlink, symlink, mkdir, rmdir, mknod, rename, setattr, getattr, etc -
It is much more related to filesystems operations other than simple character devices
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