linux-ext4 - Re: [PATCH 1/3] ext4: add EXT4_IOC

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Date:	Mon, 18 Aug 2008 10:08:11 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Theodore Tso <tytso@....edu>
CC:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/3] ext4: add EXT4_IOC_GETCRTIME ioctl

(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.
> 


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