Re: [PATCH 1/3] ext4: add EXT4_IOC_GETCRTIME ioctl

[Li Zefan <lizf@cn.fujitsu.com>]

(sorry for the so dealyed reply, I was offline last week.)

Theodore Tso wrote:
> On Wed, Aug 06, 2008 at 05:09:07PM +0800, Li Zefan wrote:
>> +	case EXT4_IOC_GETCRTIME:
>> +		return put_user(ei->i_crtime, (struct timespec __user *)arg);
>> +
> 
> I'm worried about writing a struct timespec directly to user space,
> because the kernel's idea of what is struct timespec might not be the
> same as the userspace's understanding of struct timespec ---

We have system call nanosleep(), which copies a struct timespec directly
from user space.

> specifically, because of the question of the width of time_t might be
> different in the kernel and in userspace on different architectures.
> 

But timeval.tv_sec is also of type time_t. Also sys_time() writes a time_t
directry to user space.

I should not use put_user() though...

+		return copy_to_user((struct timespec __user *)arg,
+ 			&ei->i_crtime, sizeof(ei->i_crtime));

> I think we would be better off explicitly defining a structure, or
> just returning the seconds and nanoseconds in explicit primitive
> types.
>