linux-kernel - Re: [PATCH 3.12-rc7] KVM: Fix modprobe failure for kvm_intel/kvm

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Message-ID: <52712EE9.9050402@redhat.com>
Date:	Wed, 30 Oct 2013 17:08:09 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tim Gardner <tim.gardner@...onical.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Gleb Natapov <gleb@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM list <kvm@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 3.12-rc7] KVM: Fix modprobe failure for kvm_intel/kvm_amd

Il 30/10/2013 16:59, Greg KH ha scritto:
>> > Even if it is okay to exit and not create the files (and I think it's a
>> > bit surprising), I'd like at least a printk to signal what's happening.
>> >  But there should be no reason for debugfs directory creation to fail in
>> > the end, except for basic mistakes such as the one that Tim reported, so
>> > I think it's better to report the failure.
> Creation will "fail" if debugfs is not enabled, so spiting out printk
> messages in that case is not a good idea.

Interestingly, if debugfs is not enabled we are already returning an
error-valued pointer:

static inline struct dentry *debugfs_create_dir(const char *name,
                                                struct dentry *parent)
{
        return ERR_PTR(-ENODEV);
}

which would oops a lot of the current callers.  Very few places use the
currently correct idiom

	if (IS_ERR(root) || !root)

but it's very ugly...  Perhaps debugfs_create_dir *should* return an
error-valued pointer after all.

Paolo
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