On Mon, May 18, 2026 at 05:01:41PM +0100, Jonathan Cameron wrote:
> On Thu, 14 May 2026 15:13:20 -0700
> Alison Schofield <[email protected]> wrote:
>
> > On Thu, May 14, 2026 at 07:37:49PM +0100, Jonathan Cameron wrote:
> > > On Thu, 14 May 2026 14:32:34 +0800
> > > Chen Pei <[email protected]> wrote:
> > >
> > > > kmod_module_probe_insert_module() is supposed to return 0 for builtin
> > > > modules, but only when libkmod can locate the modules.builtin index. If
> > > > the index is missing or out of sync, libkmod falls through to the real
> > > > init_module() syscall and returns an error such as -ENOENT, producing a
> > > > spurious "insert failure" even though the driver is already part of the
> > > > running kernel.
> > > >
> > > > Pre-check kmod_module_get_initstate() and short-circuit when the module
> > > > is KMOD_MODULE_BUILTIN or KMOD_MODULE_LIVE, matching the pattern used by
> > > > ndctl's own test/core.c.
> > >
> > > So I happened to run into exactly this print earlier today and was
> > > very happy to see this resolving it! I'm lazy so when developing in
> > > a VM tend to do everything I care about built in and not bother with
> > > installing the modules.
> > >
> > > However - despite having CONFIG_DEV_DAX = y in the kernel, I'm getting
> > > a state of KMOD_MODULE_COMING which is curious as there is no
> > > initstate file to read that from.
> >
> > I think this patch is worth you trying. In libmkmod code I'm looking at:
>
> It doesn't work - hence the reply!
>
> >
> > https://github.com/lucasdemarchi/kmod/blob/master/libkmod/libkmod-module.c
> >
> > the "module directory exists but initstate cannot be opened" case returns
> > KMOD_MODULE_BUILTIN, not KMOD_MODULE_COMING.
>
> I'm not following... Also...
> https://github.com/kmod-project/kmod/tree/master/libkmod
> Is a lot more recent than that tree of Lucas and I'm guessing the current
> home given it has 2 week old commits from Lucas.
>
> Can you give me a line number for the path you are talking about because even
> in that code of Lucas I'm failing to see it. Note the kmod_module_is_buitin()
> fails for the reason this patch is trying to fix. The file to check that isn't
> there - hence we hit the path that tries to figure it out from sysfs.
> I can't see any other path to a KMOD_MODULE_BUILTIN.
>
> Jonathan
Ah, thanks, I see where I went off track. Aside from looking at old
tree, I conflated kmod_module_is_builtin() w kmod_module_get_initstate()
path that this patch is actually using.
So, I think I get it now and agree w you that once the builtin lookup
path fails, we end up in sysfs probe path instead, which returns
KMOD_MODULE_COMING when both these are true:
/sys/module/name/ exists
/sys/module/name/initstate does not exist
Seems like patch needs one more case. In addition to LIVE || BUILTIN,
like:
|| (COMING && sysfs-dir-exists-without-initstate)
rather than reling on kmod_module_getinitstate() alone.
-- Alison
>
>
> >
> > So if device_dax is builtin and /sys/module/device_dax exists without
> > initstate, this patch should short-circuit before attempting insert. If
> > you still see COMING with this patch applied, then we need to figure out
> > where that state is coming from (before thinking about special casing
> > it in ndctl).
> >
> > >
> > > Looking at the code in libkmod it seems to first check if it can open
> > > /sys/modules/device_dax/initstate and if it can't checks if
> > > the directory /sys/modules/device_dax/ exists. If it finds that it returns
> > > KMOD_MODULE_COMING which seems odd given in a fully initialized built in
> > > driver
> > > that particular set of circumstances is normal.
> > >
> > > Any ideas?
> > >
> > > To me the description above is misleading if we need to have something
> > > else
> > > for the builtin case to work.
> > >
> > > I'm out of time to today but may get time to look at this tomorrow and
> > > chase
> > > down if there is a way to get it to work.
> > >
> > > Jonathan
> > >
> > >
> > > >
> > > > For builtin modules the local kmod reference is dropped because builtin
> > > > drivers cannot be unloaded; for live modules the reference is retained
> > > > in dev->module, matching the post-probe-success behavior.
> > > >
> > > > Signed-off-by: Chen Pei <[email protected]>
> > > > ---
> > > > daxctl/lib/libdaxctl.c | 18 ++++++++++++++++--
> > > > util/sysfs.c | 17 +++++++++++------
> > > > 2 files changed, 27 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/daxctl/lib/libdaxctl.c b/daxctl/lib/libdaxctl.c
> > > > index ffc81eb..42bfc39 100644
> > > > --- a/daxctl/lib/libdaxctl.c
> > > > +++ b/daxctl/lib/libdaxctl.c
> > > > @@ -910,7 +910,7 @@ static int daxctl_insert_kmod_for_mode(struct
> > > > daxctl_dev *dev,
> > > > const char *devname = daxctl_dev_get_devname(dev);
> > > > struct daxctl_ctx *ctx = daxctl_dev_get_ctx(dev);
> > > > struct kmod_module *kmod;
> > > > - int rc;
> > > > + int state, rc;
> > > >
> > > > rc = kmod_module_new_from_name(ctx->kmod_ctx, mod_name, &kmod);
> > > > if (rc < 0) {
> > > > @@ -919,7 +919,21 @@ static int daxctl_insert_kmod_for_mode(struct
> > > > daxctl_dev *dev,
> > > > return rc;
> > > > }
> > > >
> > > > - /* if the driver is builtin, this Just Works */
> > > > + /* If the driver is builtin or already live, skip probe-insert.
> > > > */
> > > > + state = kmod_module_get_initstate(kmod);
> > > > + if (state == KMOD_MODULE_BUILTIN) {
> > > > + dbg(ctx, "%s: module %s is builtin\n", devname,
> > > > + kmod_module_get_name(kmod));
> > > > + kmod_module_unref(kmod);
> > > > + return 0;
> > > > + }
> > > > + if (state == KMOD_MODULE_LIVE) {
> > > > + dbg(ctx, "%s: module %s already loaded\n", devname,
> > > > + kmod_module_get_name(kmod));
> > > > + dev->module = kmod;
> > > > + return 0;
> > > > + }
> > > > +
> > > > dbg(ctx, "%s inserting module: %s\n", devname,
> > > > kmod_module_get_name(kmod));
> > > > rc = kmod_module_probe_insert_module(kmod,
> > > > diff --git a/util/sysfs.c b/util/sysfs.c
> > > > index e027e38..641b86d 100644
> > > > --- a/util/sysfs.c
> > > > +++ b/util/sysfs.c
> > > > @@ -183,12 +183,17 @@ int __util_bind(const char *devname, struct
> > > > kmod_module *module,
> > > > }
> > > >
> > > > if (module) {
> > > > - rc = kmod_module_probe_insert_module(module,
> > > > -
> > > > KMOD_PROBE_APPLY_BLACKLIST,
> > > > - NULL, NULL, NULL,
> > > > NULL);
> > > > - if (rc < 0) {
> > > > - log_err(ctx, "%s: insert failure: %d\n",
> > > > __func__, rc);
> > > > - return rc;
> > > > + /* Skip probe-insert when the module is already builtin
> > > > or live. */
> > > > + int state = kmod_module_get_initstate(module);
> > > > +
> > > > + if (state != KMOD_MODULE_BUILTIN && state !=
> > > > KMOD_MODULE_LIVE) {
> > > > + rc = kmod_module_probe_insert_module(module,
> > > > +
> > > > KMOD_PROBE_APPLY_BLACKLIST,
> > > > + NULL,
> > > > NULL, NULL, NULL);
> > > > + if (rc < 0) {
> > > > + log_err(ctx, "%s: insert failure:
> > > > %d\n", __func__, rc);
> > > > + return rc;
> > > > + }
> > > > }
> > > > }
> > > >
> > >
>
