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Is there a macro definition to check the Linux kernel version?

Posted by: admin November 30, 2017 Leave a comment

Questions:

I’m wondering if there is a gcc macro that will tell me the Linux kernel version so I can set variable types appropriately. If not, how would I go about defining my own macro that does this?

Answers:

The linux/version.h file has a macro called KERNEL_VERSION which will let you check the version you want against the current linux headers version (LINUX_VERSION_CODE) installed. For example to check if the current Linux headers are for kernel v2.6.16 or earlier:

#include <linux/version.h>

#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,16)
...
#else
...
#endif

A better way to get the version information at run-time is to use the utsname function in include/linux/utsname.h.

char *my_kernel_version = utsname()->release;

This is essentially how /proc/version gets the current kernel verison.

See also

Getting kernel version from linux kernel module at runtime

Questions:
Answers:

gcc won’t know this information. As an alternative, you can determine a lot of kernel information at runtime easily.

You can define your runtime type like

struct unified_foo {
     unsigned int kernel_version;
     union {
         kernel_x_foo_type k_x;
         kernel_y_foo_type k_y;
         kernel_z_foo_type k_z;
     } u;
};

and have code at runtime look at /proc/version (or whatever you need from the kernel runtime environment) and set kernel_version approriately. The kernel_x_foo_type et al. is your type that you want to be conditional on the kernel version. The calling code needs to look at kernel_version and access the appropriate u.k_x, u.k_y, or u.k_z data.