Re: modprobe returns 0 upon -EEXIST from insmod

[Phil Sutter <phil@nwl.cc>]

Hi Christophe,

On Sun, Aug 17, 2025 at 05:54:27PM +0200, Christophe Leroy wrote:
> Le 17/08/2025 à 01:33, Phil Sutter a écrit :
> > [Vous ne recevez pas souvent de courriers de phil@nwl.cc. D?couvrez pourquoi ceci est important ? https://aka.ms/LearnAboutSenderIdentification ]
> > 
> > Hi,
> > 
> > I admittedly didn't fully analyze the cause, but on my system a call to:
> > 
> > # insmod /lib/module/$(uname -r)/kernel/net/netfilter/nf_conntrack_ftp.ko
> > 
> > fails with -EEXIST (due to a previous call to 'nfct add helper ftp inet
> > tcp'). A call to:
> > 
> > # modprobe nf_conntrack_ftp
> > 
> > though returns 0 even though module loading fails. Is there a bug in
> > modprobe error status handling?
> > 
> 
> Read the man page : https://linux.die.net/man/8/modprobe
> 
> In the man page I see:
> 
>             Normally, modprobe will succeed (and do nothing) if told to 
> insert a module which is already present or to remove a module which 
> isn't present.

This is not a case of already inserted module, it is not loaded before
the call to modprobe. It is the module_init callback
nf_conntrack_ftp_init() which returns -EEXIST it received from
nf_conntrack_helpers_register().

Can't user space distinguish the two causes of -EEXIST? Or in other
words, is use of -EEXIST in module_init callbacks problematic?

Cheers, Phil