Re: Checking sysctl values from within the kernel.
John Baldwin writes: | On Friday 05 August 2005 10:50 am, Dan Nelson wrote: | > In the last episode (Aug 05), Thordur I. Bjornsson said: | > > If I want to check a sysctl value from within the kernel (e.g. an | > > KLD), should I use the system calls described in sysctl(3) ? | > > | > > If not, what is the propper way to do so ? | > | > Since most sysctls are direct mappings onto integer variables in the | > kernel, just check the variable directly. | | There's also a kernel_sysctl() function available in the kernel for in-kernel | access to sysctls. You might have to lookup the OID for a given name | yourself though. Actually, there's a kernel_sysctlbyname() as well. This could be a fragile interface though. I used this scheme to do "soft-linking" between modules that could be kldloaded into the kernel or static. We called it several times every few seconds. Over time the system would wedge on a setjmp or something like that. We changed it to a function call since in a static kernel then the problem went away. Doug A. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Checking sysctl values from within the kernel.
Hi Thordur,
> PS: If you don't mind, what is a "real accessor function" ?
This is a function acting as a wrapper for accessing an integer
declared as static. This function must of course live in the same
file. This may be something like this, there may exist neater
interfaces though :
static int age;
int
age_accessor(int *get, int set)
{
if (get != NULL)
*get = age;
else if (set < 0 || set > 125)
return -1;
else
age = set;
return 0;
}
If `get' is not NULL, this means the caller wants to retrieve the
current age value. Else, this means the caller wants to set the age
value to a new one : if the latter is lower than 0 and greater than
125, this is an incredible age and the accessor reports an error.
Else it sets the new value.
I hope this helped.
Regards,
--
Jeremie Le Hen
< jeremie at le-hen dot org >< ttz at chchile dot org >
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Re: Checking sysctl values from within the kernel.
On Friday 05 August 2005 12:44 pm, Thordur I. Bjornsson wrote: > On Fri, 5 Aug 2005 11:01:32 -0400 > > John Baldwin <[EMAIL PROTECTED]> wrote: > > On Friday 05 August 2005 10:50 am, Dan Nelson wrote: > > > In the last episode (Aug 05), Thordur I. Bjornsson said: > > > > If I want to check a sysctl value from within the kernel (e.g. an > > > > KLD), should I use the system calls described in sysctl(3) ? > > > > > > > > If not, what is the propper way to do so ? > > > > > > Since most sysctls are direct mappings onto integer variables in the > > > kernel, just check the variable directly. > > > > There's also a kernel_sysctl() function available in the kernel for > > in-kernel access to sysctls. You might have to lookup the OID for a > > given name yourself though. Actually, there's a > > kernel_sysctlbyname() as well. > > > > -- > > John Baldwin <[EMAIL PROTECTED]> <>< http://www.FreeBSD.org/~jhb/ > > "Power Users Use the Power to Serve" = http://www.FreeBSD.org > > Ahh. Cool > This is not in any manpage ... > > I'm trying to understand the first argument to kernel_systcl(), > kernel_sysctl(struct thread *td, ... ) > > This thread, that it takes as an argument is this something that I need > to worry about when writing KLD's or could I just pass a NULL pointer ? > > The proplem is that I do not know/understand how threading works in the > kernel. I'll be lookin into that (although pointers are more then > welcome ;) Pass curthread as the thread. -- John Baldwin <[EMAIL PROTECTED]> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Checking sysctl values from within the kernel.
John Baldwin wrote: On Friday 05 August 2005 10:50 am, Dan Nelson wrote: In the last episode (Aug 05), Thordur I. Bjornsson said: If I want to check a sysctl value from within the kernel (e.g. an KLD), should I use the system calls described in sysctl(3) ? If not, what is the propper way to do so ? Since most sysctls are direct mappings onto integer variables in the kernel, just check the variable directly. There's also a kernel_sysctl() function available in the kernel for in-kernel access to sysctls. You might have to lookup the OID for a given name yourself though. Actually, there's a kernel_sysctlbyname() as well. Shoot, forgot about that function. However, exporting data throughout the kernel via the sysctl interface sounds like poor design. Scott ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Checking sysctl values from within the kernel.
On Fri, 5 Aug 2005 11:01:32 -0400 John Baldwin <[EMAIL PROTECTED]> wrote: > On Friday 05 August 2005 10:50 am, Dan Nelson wrote: > > In the last episode (Aug 05), Thordur I. Bjornsson said: > > > If I want to check a sysctl value from within the kernel (e.g. an > > > KLD), should I use the system calls described in sysctl(3) ? > > > > > > If not, what is the propper way to do so ? > > > > Since most sysctls are direct mappings onto integer variables in the > > kernel, just check the variable directly. > > There's also a kernel_sysctl() function available in the kernel for > in-kernel access to sysctls. You might have to lookup the OID for a > given name yourself though. Actually, there's a > kernel_sysctlbyname() as well. > > -- > John Baldwin <[EMAIL PROTECTED]> <>< http://www.FreeBSD.org/~jhb/ > "Power Users Use the Power to Serve" = http://www.FreeBSD.org Ahh. Cool This is not in any manpage ... I'm trying to understand the first argument to kernel_systcl(), kernel_sysctl(struct thread *td, ... ) This thread, that it takes as an argument is this something that I need to worry about when writing KLD's or could I just pass a NULL pointer ? The proplem is that I do not know/understand how threading works in the kernel. I'll be lookin into that (although pointers are more then welcome ;) -- Thordur I. <[EMAIL PROTECTED]> Humppa! ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Checking sysctl values from within the kernel.
On Fri, 05 Aug 2005 09:33:06 -0600 Scott Long <[EMAIL PROTECTED]> wrote: > Dan Nelson wrote: > > > In the last episode (Aug 05), Thordur I. Bjornsson said: > > > >>If I want to check a sysctl value from within the kernel (e.g. an > >>KLD), should I use the system calls described in sysctl(3) ? > >> > >>If not, what is the propper way to do so ? > > > > > > Since most sysctls are direct mappings onto integer variables in the > > kernel, just check the variable directly. > > > > Most of those integer values are also declared static, so they won't > be visible to external code, especially not kld's. > > There is no easy way to do this. I'm sure that you could hack up some > code to simulate a sysctl syscall from within the kernel, but that > would be really really gross, evil, and wrong. What values are you > trying to get at? Would it make more sense to export them via real > accessor functions? > > Scott I thought that would be a proplem. I'm trying to see the value of net.inet.tcp.drop_synfin . I could always just use the #ifdef TCP_DROP_SYNFIN wich gets set with the kernel option but that does not mean that the sysctl is set and the user/admin want's to drop SYNFIN packet's. Since I'm a novice/newbie when it comes to "kernel" programming any tips will be really good. I'll continue to search for this. PS: If you don't mind, what is a "real accessor function" ? -- Thordur I. <[EMAIL PROTECTED]> Humppa! ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Checking sysctl values from within the kernel.
On Friday 05 August 2005 10:50 am, Dan Nelson wrote: > In the last episode (Aug 05), Thordur I. Bjornsson said: > > If I want to check a sysctl value from within the kernel (e.g. an > > KLD), should I use the system calls described in sysctl(3) ? > > > > If not, what is the propper way to do so ? > > Since most sysctls are direct mappings onto integer variables in the > kernel, just check the variable directly. There's also a kernel_sysctl() function available in the kernel for in-kernel access to sysctls. You might have to lookup the OID for a given name yourself though. Actually, there's a kernel_sysctlbyname() as well. -- John Baldwin <[EMAIL PROTECTED]> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Checking sysctl values from within the kernel.
Dan Nelson wrote: In the last episode (Aug 05), Thordur I. Bjornsson said: If I want to check a sysctl value from within the kernel (e.g. an KLD), should I use the system calls described in sysctl(3) ? If not, what is the propper way to do so ? Since most sysctls are direct mappings onto integer variables in the kernel, just check the variable directly. Most of those integer values are also declared static, so they won't be visible to external code, especially not kld's. There is no easy way to do this. I'm sure that you could hack up some code to simulate a sysctl syscall from within the kernel, but that would be really really gross, evil, and wrong. What values are you trying to get at? Would it make more sense to export them via real accessor functions? Scott ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Checking sysctl values from within the kernel.
In the last episode (Aug 05), Thordur I. Bjornsson said: > If I want to check a sysctl value from within the kernel (e.g. an > KLD), should I use the system calls described in sysctl(3) ? > > If not, what is the propper way to do so ? Since most sysctls are direct mappings onto integer variables in the kernel, just check the variable directly. -- Dan Nelson [EMAIL PROTECTED] ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Checking sysctl values from within the kernel.
Hello list.
If I want to check a sysctl value from within the kernel (e.g. an KLD),
should I use the system calls described in sysctl(3) ?
If not, what is the propper way to do so ?
And if it is and I want to do error checking e.g:
if((sysctl(name, namelen, &val, NULL, 0)) != 0) {
"Error in call to sysctl(3) blah blah blah";
}
What would be the correct way to report,stop, &c ?
This is propaply depentand on what I'm doing so...
If this is A&A I'm sorry for the noize, I have not been able to find
anything on google/archives. (It's late ;)
--
Thordur I. <[EMAIL PROTECTED]>
Humppa!
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