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aCOSwt
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 Posted: Thu Jan 31, 2013 11:39 am Post subject: Using kernel headers |
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Considering a userspace application with source files including <linux/whatever.h>
What is best practice regarding the makefile ?
1/ Nothing special ! => The application *must* be built against installed linux-headers and responsibility for getting appropriate linux-headers *must* be left to who builds the application.
2/ Provide a glibc-like --with-headers configuration switch enabling who builds to set it to whatever kernel-headers path ?
In case of 2/ :
What is best practice regarding a gentoo ebuild for such a package ?
3/ hardcode --with-headers=/usr/src/linux/include ?
4/ Make the use of the kernel-headers vs linux-headers depend on some use flag setting ?
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Last edited by aCOSwt on Fri Feb 15, 2013 9:18 am; edited 3 times in total |
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Genone
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| Posted: Thu Jan 31, 2013 11:46 am Post subject: |
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Option 1), unless the application really needs headers that match the running kernel (because it interfaces with specific kernel modules or whatever).
Experts can always override/fool the build system to pickup different kernel headers. |
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aCOSwt
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| Posted: Thu Jan 31, 2013 12:03 pm Post subject: |
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| Genone wrote: | Option 1), unless the application really needs headers that match the running kernel (because it interfaces with specific kernel modules or whatever).
Experts can always override/fool the build system to pickup different kernel headers. |
The application does not really need headers that match the running kernel.
However,
Considering that there are an appreciable number of kernel patches that actually patch kernel-headers (vg : /usr/src/linux/include/*) in one way or another (including many I cannot even imagine...), the difference (and degree of incompatibility) with the linux-headers (vg : /usr/include/linux/*) can be so important that I was wondering if it is not systematically safer to build against actual kernel-headers.
(BTW, I thought it was what glibc advised, but I cannot any longer find this recommendation. Could be I am getting too old.)
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Genone
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| Posted: Thu Jan 31, 2013 1:55 pm Post subject: |
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| Userspace applications should always use the distro supplied, sanitized kernel headers in /usr/include/linux, as that is what glibc and others use. Building against the running kernel headers would therefore cause the compability issues you mention. See http://linuxmafia.com/faq/Kernel/usr-src-linux-symlink.html why using "live" headers is bad. |
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aCOSwt
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| Posted: Fri Feb 01, 2013 6:35 am Post subject: |
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| http://linuxmafia.com/faq/Kernel/usr-src-linux-symlink.html wrote: | | Boom! Do you see the disconnect? |
 Bham ! Yes I do !
Thank you Genone.
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Don't try to understand my posts. Immanuel Kant never did, he thinks that only music and laughter do not have to mean anything. |
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aCOSwt
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| Posted: Fri Feb 15, 2013 9:27 am Post subject: |
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| Genone wrote: | | Userspace applications should always use the distro supplied, sanitized kernel headers in /usr/include/linux, as that is what glibc and others use. |
Hmmm... not that much solved and I am getting even more confused :
As a matter of fact, the glibc comes with its own headers that slightly differ from the kernel headers.
As an example is /usr/include/sched.h (glibc's) differing from /usr/include/linux/sched.h (kernel-headers')
If, for example, I want to use the libc's subroutine sched_setscheduler, should I include <sched.h> or <linux/sched.h> ?
BTW, man says <sched.h> ! 
Man's solution not being very convenient, I admit, because I am forced to read the header to understand that, in reality, I should :
#define __USE_GNU
#include <sched.h>
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Genone
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| Posted: Fri Feb 15, 2013 12:50 pm Post subject: |
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| aCOSwt wrote: | | Genone wrote: | | Userspace applications should always use the distro supplied, sanitized kernel headers in /usr/include/linux, as that is what glibc and others use. |
Hmmm... not that much solved and I am getting even more confused :
As a matter of fact, the glibc comes with its own headers that slightly differ from the kernel headers.
As an example is /usr/include/sched.h (glibc's) differing from /usr/include/linux/sched.h (kernel-headers') |
If glibc installs its own header then of course userspace applications should use that one. My statement was only referring to /usr/include/linux vs. /usr/src/linux/include/linux |
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