linux-kernel - Re: [PATCH -V4 08/11] vfs: Add new file and directory create permission flags

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Message-Id: <B0449E28-B18A-4009-B6CA-8AEED22F4CD7@dilger.ca>
Date:	Sun, 2 Jan 2011 22:20:08 -0700
From:	Andreas Dilger <adilger@...ger.ca>
To:	Ted Ts'o <tytso@....edu>
Cc:	Andreas Gruenbacher <agruen@...e.de>,
	Jeff Layton <jlayton@...hat.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	"sfrench@...ibm.com" <sfrench@...ibm.com>,
	"ffilz@...ibm.com" <ffilz@...ibm.com>,
	"adilger@....com" <adilger@....com>,
	"sandeen@...hat.com" <sandeen@...hat.com>,
	"bfields@...i.umich.edu" <bfields@...i.umich.edu>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"nfsv4@...ux-nfs.org" <nfsv4@...ux-nfs.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -V4 08/11] vfs: Add new file and directory create permission flags

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@....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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