Hi Goffredo,
On 01/08/2013 01:32 AM, Goffredo Baroncelli wrote:
> Hi Jeff,
>
> On 01/07/2013 07:24 AM, Jeff Liu wrote:
>> Hi,
>> On 01/07/2013 02:44 AM, Goffredo Baroncelli wrote:
>>> Hi Jeff,
>>>
>>> On 01/05/2013 03:48 AM, Jeff Liu wrote:
>>>> Add a new ioctl(2) BTRFS_IOC_GET_FSLABLE, so that we can get the label
>>>> upon a mounted filesystem.
>>>>
>>>> Signed-off-by: Jie Liu <[email protected]>
>>>> Signed-off-by: Anand Jain <[email protected]>
>>>> Cc: Miao Xie <[email protected]>
>>>> Cc: Goffredo Baroncelli <[email protected]>
>>>> Cc: David Sterba <[email protected]>
>>>>
>>>> ---
>>>> fs/btrfs/ioctl.c | 21 +++++++++++++++++++++
>>>> fs/btrfs/ioctl.h | 2 ++
>>>> 2 files changed, 23 insertions(+)
>>>>
>>>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>>>> index 8fcf9a5..ef2f55a 100644
>>>> --- a/fs/btrfs/ioctl.c
>>>> +++ b/fs/btrfs/ioctl.c
>>>> @@ -3699,6 +3699,25 @@ out:
>>>> return ret;
>>>> }
>>>>
>>>
>>> May be that it was already discussed, and I am missing something, but if
>>> we check the label length we should terminate the string with a zero in
>>> case this is too long...
>>>
>>> However this is a minor bug, please push this patch forward..
>> I don't think so.
>> Why we need to terminate the string with a zero?
>> We have already truncated the label string up to maximum 255 bytes if it
>> was too long.
>>
>> Consider the normal conditions, i.e. the label string is less than 256,
>> we just copy it back to the user without a terminated NUL.
>
> Sorry I don't understand the reason to terminate the string up to 255
> chars without adding a zero. Or we copy all the buffer (BTRFS_LABEL_SIZE
> characters without furthers checks) or we copy BTRFS_LABEL_SIZE-1
> characters, adding a zero at the end.
For normal cases, there should already has a NUL at the end of the input
label string when performing btrfs_ioc_set_fslabel(), and we have also
added a NUL for unmounted label set in btrfs-progs. In both cases, put
it again on btrfs_ioc_get_fslabel() is redundant IMO.
If we ran into a too long label, return the first 255 bytes is fine for
both mounted and unmounted get_label() routines in btrfs-progs since I
did memset(label, 0, sizeof(label)) at first for fetching mounted fs label.
Also, I have not found any existing kernel code does similar things by
adding a NUL to end up a char array, could you show me an example?
"""Or we copy all the buffer(BTRFS_LABEL_SIZE) characters without
furthers checks"""
If an array is capable of N chars, we can only full it with N - 1 chars.
Thanks,
-Jeff
>>>
>>>
>>>> +static int btrfs_ioctl_get_fslabel(struct file *file, void __user *arg)
>>>> +{
>>>> + struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
>>>> + const char *label = root->fs_info->super_copy->label;
>>>> + size_t len = strnlen(label, BTRFS_LABEL_SIZE);
>>>> + int ret;
>>> + int label_is_too_long = 0;
>> bool label_is_too_long = false;
>>>> +
>>>> + if (len == BTRFS_LABEL_SIZE) {
>>>> + pr_warn("btrfs: label is too long, return the first %zu
>>>> bytes\n",
>>>> + --len);
>>>
>>> + label_is_too_long = 1;
>> label_is_too_long = true;
>>>> + }
>>>> +
>>>> + mutex_lock(&root->fs_info->volume_mutex);
>>>> + ret = copy_to_user(arg, label, len);
>>> + if (!ret && label_is_too_long)
>>> + ret = copy_to_user(arg+BTRFS_LABEL_SIZE, "", 1);
>> Hmm? ret = copy_to_user(arg + len, "", 1);
>>
> My idea was to put a zero at the end of the string, but I did a mistake
> with the cut&paste.. sorry :-)
>
>>>> + mutex_unlock(&root->fs_info->volume_mutex);
>> If you or anyone has objection to this patch, please just post yours, I
>> won't follow it up again.
>
> Sorry I don't want to bother anybody, I know that reviewing a patch nine
> times is a very havvy work. I (and I think more other peoples) really
> appreciate your efforts.
>
> BR
> G.Baroncelli
>
>>>> +
>>>> + return ret ? -EFAULT : 0;
>>>> +}
>>>> +
>>>> long btrfs_ioctl(struct file *file, unsigned int
>>>> cmd, unsigned long arg)
>>>> {
>>>> @@ -3797,6 +3816,8 @@ long btrfs_ioctl(struct file *file, unsigned int
>>>> return btrfs_ioctl_qgroup_create(root, argp);
>>>> case BTRFS_IOC_QGROUP_LIMIT:
>>>> return btrfs_ioctl_qgroup_limit(root, argp);
>>>> + case BTRFS_IOC_GET_FSLABEL:
>>>> + return btrfs_ioctl_get_fslabel(file, argp);
>>>> }
>>>>
>>>> return -ENOTTY;
>>>> diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
>>>> index 731e287..5b2cbef 100644
>>>> --- a/fs/btrfs/ioctl.h
>>>> +++ b/fs/btrfs/ioctl.h
>>>> @@ -451,6 +451,8 @@ struct btrfs_ioctl_send_args {
>>>> struct btrfs_ioctl_qgroup_create_args)
>>>> #define BTRFS_IOC_QGROUP_LIMIT _IOR(BTRFS_IOCTL_MAGIC, 43, \
>>>> struct btrfs_ioctl_qgroup_limit_args)
>>>> +#define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
>>>> + char[BTRFS_LABEL_SIZE])
>>>> #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
>>>> struct btrfs_ioctl_get_dev_stats)
>>>> #endif
>>>
>>>
>>
>>
>
>
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