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SubjectRe: Kernel module version support.
Date
In message <957BD1C2BF3CD411B6C500A0C944CA2602AFADC0@pdsmsx32.pd.intel.com> you
write:
> Hi, Rusty
> I am interested in your module version support implementation. I've read
> your description about it.

Cool. That reminds me.

> 1. How do you plan to store the version information of a kernel module that
> will export some symbols?
> (In the version table of "bzImage"? In a specified section in this kernel
> module? In other place? Or don't
> store?)

Currently I don't do this. I discussed solutions briefly with Kai
some time ago, but I'll have to revisit it. Getting the core kernel
symbols versioned covers 90% of the problem though, and shows the
validity of the approach.

> 2. You mentioned that "modules which want to export symbols place
> their full path name in the .needmodversion section. Just before the
> kernel is linked, these names are extracted, and genksyms scans
> those files to create a version table. This table is then linked
> into the kernel". And I think we must recalculate all version
> informaiton every time when we re built the kernel in this way. Why
> don't we place all the module version information in some files just
> like old days.

That's a build system detail: it can use that list to generate the
versions on demand of course.

> 3. You mentioned that "these symbol versions are then checked on
> insmod". I wanna whether it means you would like to restore the
> "/proc/ksyms" file or QUERY_MODULE SYSCALL to export the kernel
> version table to the user space application.

The language is a little loose. The kernel does the actual checking:

#ifdef CONFIG_MODVERSIONING
static inline int check_version(const char *name,
const char *symname,
const struct modversion_info *versions,
unsigned int num)
{
unsigned int i, k;

/* First search kernel (unversioned symbols not listed). */
for (k = 0; !streq(modversions[k].symbol, symname); k++)
if (!modversions[k].symbol[0])
return 0;

/* Now see if module has matching symbol. */
for (i = 0; i < num; i++) {
if (streq(versions[i].symbol, symname)) {
if (versions[i].checksum == modversions[k].checksum)
return 0;
printk("%s: disagrees about version of symbol %s\n",
name, symname);
DEBUGP("Kernel checksum %lX vs module %lX\n",
modversions[k].checksum, versions[i].checksum);
return -ESRCH;
}
}

/* Not in module's version table. OK, but that taints the kernel. */
printk("%s: no version for %s found: kernel tainted.\n",
name, symname);
tainted |= TAINT_FORCED_MODULE;
return 0;
}

Hope that clarifies,
Rusty.
PS. I'll update the patch soon, I promise...
--
Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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