Re: [PATCH 3.12-rc7] KVM: Fix modprobe failure for kvm_intel/kvm_amd

From: Paolo Bonzini
Date: Wed Oct 30 2013 - 12:41:34 EST

Il 30/10/2013 17:23, Greg KH ha scritto:
>> > 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.
> It will oops? Really? Where? That shouldn't happen at all.

Doh, it obviously won't because the bogus pointer value will never be
dereferenced by the dummy debugfs_create_file.

>> > 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.
> Or just don't care about the return value, and all will work out just
> fine, right?

Debugfs files would then be created in the debugfs root, which is not nice.

/* If the parent is not specified, we create it in the root.
* We need the root dentry to do this, which is in the super
* block. A pointer to that is in the struct vfsmount that we
* have around.
if (!parent)
parent = debugfs_mount->mnt_root;

This is all documented right:

* debugfs_create_file - create a file in the debugfs filesystem
* ...
* This function will return a pointer to a dentry if it succeeds. This
* pointer must be passed to the debugfs_remove() function when the file is
* to be removed (no automatic cleanup happens if your module is unloaded,
* you are responsible here.) If an error occurs, %NULL will be returned.
* If debugfs is not enabled in the kernel, the value -%ENODEV will be
* returned.

so I guess it's just part of the API.

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