linux-kernel - Re: [PATCH 3/4] kmod: Return directly if module name is empty in request

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Message-ID: <20200418071905.GE11244@42.do-not-panic.com>
Date:   Sat, 18 Apr 2020 07:19:05 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>, Jessica Yu <jeyu@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH 3/4] kmod: Return directly if module name is empty in
 request_module()

On Sat, Apr 18, 2020 at 01:58:45PM +0800, Tiezhu Yang wrote:
> On 04/18/2020 01:48 PM, Luis Chamberlain wrote:
> > On Fri, Apr 17, 2020 at 11:45 PM Luis Chamberlain <mcgrof@...nel.org> wrote:
> > > On Sat, Apr 18, 2020 at 01:19:59PM +0800, Tiezhu Yang wrote:
> > > > If module name is empty, it is better to return directly at the beginning
> > > > of request_module() without doing the needless call_modprobe() operation.
> > > > 
> > > > Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> > > > ---
> > > >   kernel/kmod.c | 5 +++++
> > > >   1 file changed, 5 insertions(+)
> > > > 
> > > > diff --git a/kernel/kmod.c b/kernel/kmod.c
> > > > index 3cd075c..5851444 100644
> > > > --- a/kernel/kmod.c
> > > > +++ b/kernel/kmod.c
> > > > @@ -28,6 +28,8 @@
> > > > 
> > > >   #include <trace/events/module.h>
> > > > 
> > > > +#define MODULE_NOT_FOUND 256
> > > > +
> > > >   /*
> > > >    * Assuming:
> > > >    *
> > > > @@ -144,6 +146,9 @@ int __request_module(bool wait, const char *fmt, ...)
> > > >        if (ret >= MODULE_NAME_LEN)
> > > >                return -ENAMETOOLONG;
> > > > 
> > > > +     if (strlen(module_name) == 0)
> > > > +             return MODULE_NOT_FOUND;
> > > I'd rather we just use something standard like -EINVAL.
> > > What do we return if its not found? Then use that value.
> > Also, are we testing for this condition yet? If not can we add one?
> 
> Yes, kmod_test_0001_driver() in tools/testing/selftests/kmod/kmod.sh tests
> this case and expects result MODULE_NOT_FOUND which is 256.

OK I see now I had put:

errno_name_to_val()                                                             
{                                                                               
        case "$1" in                                                            
	# kmod calls modprobe and upon of a module not found                    
	# modprobe returns just 1... However in the
	# kernel we *sometimes* see 256... 
	MODULE_NOT_FOUND)                                                       
		echo 256;;

I found that through testing, however there was nothing set in stone,
nothing documented. While you are at it, can you find the places where
this is returned in the kernel code? We should clear this up and
se things straight. We cannot change what we gave userspace already
though.

  Luis