> Actually, I think it is required by POSIX that EXDEV is returned when cross-linking files. For mv calling rename() at least it uses a return EXDEV to copy the file to the target filesystem instead of just giving up and returning an error. It may be other applications like tar have a similar dependency for link().
>
> Cheers, Andreas
>
> On 2011-01-02, at 16:21, Ted Ts'o <tytso@mit.edu> wrote:
>
>> I was going through some old patches in the ext4 patchwork list, and
>> came across this. It looks like this patch has never been applied to
>> mainline. If it's a "clear improvement", any reason not to submit it?
>>
>> Regards,
>>
>> - Ted
>>
>> On Mon, Sep 27, 2010 at 03:14:00PM +0200, Andreas Gruenbacher wrote:
>>>
>>> Ah, you mean this:
>>>
>>> --- a/fs/namei.c
>>> +++ b/fs/namei.c
>>> @@ -2450,7 +2450,9 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
>>> if (!inode)
>>> return -ENOENT;
>>>
>>> - error = may_create(dir, new_dentry, S_ISDIR(inode->i_mode));
>>> + if (S_ISDIR(inode->i_mode))
>>> + return -EPERM;
>>> + error = may_create(dir, new_dentry, 0);
>>> if (error)
>>> return error;
>>>
>>> @@ -2464,8 +2466,6 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
>>> return -EPERM;
>>> if (!dir->i_op->link)
>>> return -EPERM;
>>> - if (S_ISDIR(inode->i_mode))
>>> - return -EPERM;
>>>
>>> error = security_inode_link(old_dentry, dir, new_dentry);
>>> if (error)
>>>
>>> This is a clear improvement; I don't think it matters that user-space will
>>> get -EPERM instead of -EXDEV when trying to hard-link a directory across
>>> devices.
>>>
>>> Thanks,
>>> Andreas
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