Date: Sun, 22 Mar 2015 18:26:50 +0800 From: Tiwei Bie <btw@mail.ustc.edu.cn> To: Mateusz Guzik <mjguzik@gmail.com> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-hackers@freebsd.org Subject: Re: [PATCH] Finish the task 'Validate coredump format string' Message-ID: <20150322102650.GA14629@freebsd> In-Reply-To: <20150322101401.GH14650@dft-labs.eu> References: <1426946345-67889-1-git-send-email-btw@mail.ustc.edu.cn> <20150321200500.GC14650@dft-labs.eu> <20150322091853.GA89976@freebsd> <20150322101401.GH14650@dft-labs.eu>
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On Sun, Mar 22, 2015 at 11:14:01AM +0100, Mateusz Guzik wrote:
> On Sun, Mar 22, 2015 at 05:19:40PM +0800, Tiwei Bie wrote:
> [..]
>
> I was somehow convinced that tunables are dealt with other code.
>
> If such sysctl handler is also called for tunables, the kernel should
> pass a flag or some other indicator so that the function knows it is
> dealing with a tunable and that would avoid locking and thus solve the
> problem.
>
If a sysctl is registered as a tunable (CTLFLAG_TUN), when calling
sysctl_register_oid(), sysctl_load_tunable_by_oid_locked() will be
called to fetch the kenv setting (i.e. tunable setting defined in
loader.conf) to update the sysctl setting:
void
sysctl_register_oid(struct sysctl_oid *oidp)
{
......
if ((oidp->oid_kind & CTLTYPE) != CTLTYPE_NODE &&
#ifdef VIMAGE
(oidp->oid_kind & CTLFLAG_VNET) == 0 &&
#endif
(oidp->oid_kind & CTLFLAG_TUN) != 0 &&
(oidp->oid_kind & CTLFLAG_NOFETCH) == 0) {
sysctl_load_tunable_by_oid_locked(oidp);
}
}
sysctl_load_tunable_by_oid_locked() will fetch the kenv setting, and
call the sysctl handler, e.g. sysctl_kern_corefile() to update the
sysctl setting:
static void
sysctl_load_tunable_by_oid_locked(struct sysctl_oid *oidp)
{
......
case CTLTYPE_STRING:
penv = kern_getenv(path + rem);
if (penv == NULL)
return;
req.newlen = strlen(penv);
req.newptr = penv;
break;
default:
return;
}
error = sysctl_root_handler_locked(oidp, oidp->oid_arg1,
oidp->oid_arg2, &req);
if (error != 0)
printf("Setting sysctl %s failed: %d\n", path, error);
......
}
The tunable setting is just a "name"=value format in kenv. And the kenv
codes have no idea of the meaning of the "name". It can also be modified
later when system is up by `kenv' command. And the corresponding sysctl
setting won't be affected any more.
> I'm wondering if we should go a little bit further and get rid of
> static char corefilename[MAXPATHLEN]
>
> and have a static char *corefilename instead.
>
> A dedicated sysinit func could fetch and validate the tunable, if any.
> If no tunable was provided it would alloc memory for the default.
>
> --
> Mateusz Guzik <mjguzik gmail.com>
Best regards,
Tiwei Bie
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