Re: [kmod][PATCH] module: fix error path in kmod_module_probe_insert_module()

[Lucas De Marchi]

On Sun, May 26, 2019 at 11:25:12AM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
>
> The documentation says that kmod_module_probe_insert_module() will
> return >0 if "stopped by a reason given in @flags" but it returns a
> negative value if KMOD_PROBE_FAIL_ON_LOADED flag is passed and the
> relevant module is already loaded. Fix the error path by using a
> positive error value where required.
>
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> ---
> libkmod/libkmod-module.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/libkmod/libkmod-module.c b/libkmod/libkmod-module.c
> index bffe715..a3afaba 100644
> --- a/libkmod/libkmod-module.c
> +++ b/libkmod/libkmod-module.c
> @@ -1253,7 +1253,7 @@ KMOD_EXPORT int kmod_module_probe_insert_module(struct kmod_module *mod,
> 	if (!(flags & KMOD_PROBE_IGNORE_LOADED)
> 					&& module_is_inkernel(mod)) {
> 		if (flags & KMOD_PROBE_FAIL_ON_LOADED)
> -			return -EEXIST;
> +			return EEXIST;
> 		else
> 			return 0;
> 	}
> @@ -1304,7 +1304,7 @@ KMOD_EXPORT int kmod_module_probe_insert_module(struct kmod_module *mod,
> 						&& module_is_inkernel(m)) {
> 			DBG(mod->ctx, "Ignoring module '%s': already loaded\n",
> 								m->name);
> -			err = -EEXIST;
> +			err = EEXIST;

this would break the ABI. modprobe for instance, that is in the same
repository would be broken by it:

kmod_list_foreach() {
	...
	if (err >= 0)
		/* ignore flag return values such as a mod being blacklisted */
		err = 0;
	else {
		switch (err) {
		case -EEXIST:
	...
}

I think we need to say the bug is actually in the bad documentation - my
bad actually, on commit b1a51256a9ed ("libkmod-module: probe: change
insertion to cover more use cases").

If you look at the definition of 'enum kmod_probe' you will see that
not all flags are returned as positive values - the only values that
have this behavior are the ones related to blacklist.

Could you rather patch the documentation?

thanks
Lucas De Marchi

> 			goto finish_module;
> 		}
>
> @@ -1340,14 +1340,14 @@ finish_module:
> 		 * been loaded between the check and the moment we try to
> 		 * insert it.
> 		 */
> -		if (err == -EEXIST && m == mod &&
> +		if (err == EEXIST && m == mod &&
> 				(flags & KMOD_PROBE_FAIL_ON_LOADED))
> 			break;
>
> 		/*
> 		 * Ignore errors from softdeps
> 		 */
> -		if (err == -EEXIST || !m->required)
> +		if (err == EEXIST || !m->required)
> 			err = 0;
>
> 		else if (err < 0)
> --
> 2.21.0