compiler errors - "'errno' undeclared" when compile Linux kernel -

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i'm trying compile , keep getting following error: enter image description here

i've included asm-i386/errno.h once , didn't work. i've tried including linux/errno.h , didn't work ether.

what file should include?

there no errno variable in linux kernel: variable lives in user space only.

if kernel function wants report error , specify error code, encapsulates error code returning value. there 3 possibilities of such encapsulation, dependent value type returned on success:

  1. function returns 0 on success, negated error code on fail.

this used convention referenced 0/-err.

  1. function returns valid pointer on success, expression err_ptr(err) on fail.

this expression evaluated pointer, can never points real kernel object. convention may used if null valid result.

  1. function returns positive integer on success, negated error code on fail: +val/-err.

in case when 0 valid result, convention may used too: +val/0/-err.

when user space library needs set errno according kernel's request, checks result of system call (which way perform request kernel). dependent on syscall, either 1 or 3 convention used (return type of system call long).

example of "setting" errno in kernel space user space see here.


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