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Date: Wed, 28 Nov 2012 18:25:46 +0800
From: Miao Xie <miaox@cn.fujitsu.com>
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To: Anand Jain <Anand.Jain@oracle.com>
CC: linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v3] Btrfs: add label to snapshot and subvol
References: <1351766770-4044-1-git-send-email-Anand.Jain@oracle.com> <1354040960-31522-1-git-send-email-Anand.Jain@oracle.com> <1354040960-31522-2-git-send-email-Anand.Jain@oracle.com> <50B57F63.4050205@cn.fujitsu.com> <50B5E150.4050402@oracle.com>
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On 	wed, 28 Nov 2012 18:02:56 +0800, Anand Jain wrote:
> 
> 
> On 11/28/2012 11:05 AM, Miao Xie wrote:
>> On wed, 28 Nov 2012 02:29:17 +0800, Anand jain wrote:
>>>   /*
>>> @@ -2441,6 +2443,14 @@ static inline bool btrfs_root_readonly(struct btrfs_root *root)
>>>   {
>>>       return (root->root_item.flags & cpu_to_le64(BTRFS_ROOT_SUBVOL_RDONLY)) != 0;
>>>   }
>>> +static inline char * btrfs_root_label(struct btrfs_root_item *root_item)
>>> +{
>>> +    return (root_item->label);
>>> +}
>>> +static inline void btrfs_root_set_label(struct btrfs_root_item *root_item, char *val)
>>> +{
>>> +    memcpy(root_item->label, val, BTRFS_SUBVOL_LABEL_SIZE);
>>> +}
>>>
>>>   /* struct btrfs_root_backup */
>>>   BTRFS_SETGET_STACK_FUNCS(backup_tree_root, struct btrfs_root_backup,
>>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>>> index e58bd9d..f0b3d9d 100644
>>> --- a/fs/btrfs/ioctl.c
>>> +++ b/fs/btrfs/ioctl.c
>>> @@ -3725,6 +3725,57 @@ static int btrfs_ioctl_set_label(struct btrfs_root *root, void __user *arg)
>>>       return 0;
>>>   }
>>>
>>> +static int btrfs_ioctl_subvol_getlabel(struct btrfs_root *root,
>>> +                        void __user *arg)
>>> +{
>>> +    char *label;
>>> +
>>> +    label = btrfs_root_label(&root->root_item);
>>> +    if (copy_to_user(arg, label, BTRFS_SUBVOL_LABEL_SIZE))
>>> +        return -EFAULT;
>>
>> we also need lock here.
> 
>  yes. wish memcpy is atomic.
> 
>>> +    return 0;
>>> +}
>>> +
>>> +static int btrfs_ioctl_subvol_setlabel(struct file *file,
>>> +                        void __user *arg)
>>> +{
>>> +    char label[BTRFS_SUBVOL_LABEL_SIZE+1];
>>> +    struct btrfs_trans_handle *trans;
>>> +    struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
>>> +    struct inode *inode = file->f_path.dentry->d_inode;
>>> +    int ret;
>>> +
>>> +    if (btrfs_root_readonly(root))
>>> +        return -EROFS;
>>> +
>>> +    if (!inode_owner_or_capable(inode))
>>> +        return -EACCES;
>>> +
>>> +    ret = mnt_want_write_file(file);
>>> +    if (ret)
>>> +        return ret;
>>> +
>>> +    if (copy_from_user(label, arg, BTRFS_SUBVOL_LABEL_SIZE)) {
>>> +        ret = -EFAULT;
>>> +        goto out;
>>> +    }
>>> +
>>> +    mutex_lock(&inode->i_mutex);
>>
>> we should use a lock which belongs to the root not inode.
> 
> 
>  I couldn't find an already defined lock which would exactly
>  fit the purpose here. Do you have any idea ?

I thinks we may use ->root_times_lock, but we need change the name
to make it suitable for its role.

Thanks
Miao

> 
> 
> Thanks, Anand
> 
> 
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