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Date: Wed, 28 Nov 2012 18:02:56 +0800
From: Anand Jain <Anand.Jain@oracle.com>
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To: miaox@cn.fujitsu.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>
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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 ?


Thanks, Anand