Sorry for my late response, I missed your feedback somehow.
On 12/12/2012 12:15 PM, Miao Xie wrote:
> On wed, 12 Dec 2012 11:23:00 +0800, Jeff Liu wrote:
>> Add a new ioctl BTRFS_FS_SETLABEL to change the label of a mounted filesystem.
>>
>>
>> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
>> Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
>>
>> ---
>> fs/btrfs/ioctl.c | 34 ++++++++++++++++++++++++++++++++++
>> fs/btrfs/ioctl.h | 2 ++
>> 2 files changed, 36 insertions(+)
>>
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index b0a5e17..ebbf634 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -3711,6 +3711,38 @@ static int btrfs_ioctl_get_fslabel(struct btrfs_root *root, void __user *arg)
>> return ret ? -EFAULT : 0;
>> }
>>
>> +static int btrfs_ioctl_set_fslabel(struct btrfs_root *root, void __user *arg)
>> +{
>> + struct btrfs_super_block *super_block = root->fs_info->super_copy;
>> + struct btrfs_trans_handle *trans;
>> + char label[BTRFS_LABEL_SIZE];
>> + int ret = 0;
>> +
>> + if (!capable(CAP_SYS_ADMIN))
>> + return -EPERM;
>> +
>> + if (btrfs_root_readonly(root))
>> + return -EROFS;
>
> Since this label is a global parameter, we needn't check the root
> is R/O or not.
>
> The check we need is the write access of the fs, so we need call
> mnt_want_write_file()
Yes, you are right.
>
>> +
>> + if (copy_from_user(label, arg, sizeof(label)))
>> + return -EFAULT;
>> +
>> + label[BTRFS_LABEL_SIZE - 1] = '\0';
>
> I don't think setting the last byte to '\0' is a good way, because the user would be
> very strange that the new label is truncated, but the program told him that it was done
> successfully.
Good point, will revise it later.
Thanks,
-Jeff
>
>> +
>> + mutex_lock(&root->fs_info->volume_mutex);
>> + trans = btrfs_start_transaction(root, 1);
>> + if (IS_ERR(trans)) {
>> + ret = PTR_ERR(trans);
>> + goto out_unlock;
>> + }
>> + strcpy(super_block->label, label);
>> + btrfs_end_transaction(trans, root);
>> +
>> +out_unlock:
>> + mutex_unlock(&root->fs_info->volume_mutex);
>> + return ret;
>> +}
>> +
>> long btrfs_ioctl(struct file *file, unsigned int
>> cmd, unsigned long arg)
>> {
>> @@ -3811,6 +3843,8 @@ long btrfs_ioctl(struct file *file, unsigned int
>> return btrfs_ioctl_qgroup_limit(root, argp);
>> case BTRFS_IOC_GET_FSLABEL:
>> return btrfs_ioctl_get_fslabel(root, argp);
>> + case BTRFS_IOC_SET_FSLABEL:
>> + return btrfs_ioctl_set_fslabel(root, argp);
>> }
>>
>> return -ENOTTY;
>> diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
>> index 98f896f..cc4e657 100644
>> --- a/fs/btrfs/ioctl.h
>> +++ b/fs/btrfs/ioctl.h
>> @@ -455,4 +455,6 @@ struct btrfs_ioctl_send_args {
>> struct btrfs_ioctl_get_dev_stats)
>> #define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 53, \
>> char[BTRFS_LABEL_SIZE])
>> +#define BTRFS_IOC_SET_FSLABEL _IOW(BTRFS_IOCTL_MAGIC, 54, \
>> + char[BTRFS_LABEL_SIZE])
>> #endif
>
> number 50 has been reserved for this feature.
>
> Thanks
> Miao
>
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