Convert timeval to timespec

ranthal · 07-02-2009, 05:25 PM

Hey all,

I have some code that was written by a partner of mine originally for user space and now I need to implement it as a module in kernel space. One of the functions in the code sets the system time. It originally used settimeofday with a timeval stuct passed in but the kernel space equivalent do_settimeofday takes a timepsec struct instead so I need to convert the timeval to a timespec. Has anyone done this before and knows a good way to do it?

Digging through the source I didn't see any function that directly converts it but I did find:

Code:

static inline s64 timeval_to_ns(const struct timeval *tv);
extern struct timespec ns_to_timespec(const s64 nsec);

You can probably guess where I'm going with that. What the hell is an s64 type?

Also from linux/time.h that might help:

Code:

struct timespec {
    time_t tv_sec;
    long   tv_nsec;
};

struct timeval {
    time_t      tv_sec;
    suseconds_t tv_usec;
};

jf.argentino · 07-03-2009, 09:47 AM

That's not so difficult! Or am I missing something?
How many ns in 1 us... 1000 so just multiply tv_usec by 1000 to get tv_nsec, and divide tv_nsec per 1000 to have the tv_usec, you can round it too...

ranthal · 07-06-2009, 04:28 PM

Quote:

Originally Posted by jf.argentino

That's not so difficult! Or am I missing something?

No you're right, it's not very difficult. It was more a question I was raising since I hadn't worked with timespecs at all before so I wanted to ensure the approach I was taking is correct. Currently I have it implemented as such:

Code:

struct timeval tv
struct timespec ts;
s64 nsec;

do_gettimeofday(&tv);

nsec = timeval_to_ns(&tv);
ts = ns_to_timespec(nsec);

Seems simple enough but there's certain things I want to make sure I have covered. For instance, does this handle the assignment of the tv_sec member variables or is it concerned with only the usec to nsec? ns_to_timespec returns a timespec struct, not just a long value that would be consistent with operating solely on the nsec memeber. Hopefully if the design of the function is consistent then it handles both.

I've yet to look past the header file into the source C file. I'll do that when I get the chance, hopefully in about 30 mins or so.

ranthal · 07-06-2009, 06:31 PM

Checked out the source code and it definitely has me covered. timeval_to_ns is an inline and you can see in time.h it has a tv->tv_sec * NS_PER_TSEC evaluation. ns_to_timespec is in time.c and it is also apparent that it handles the tsec value as well. I'll update if something comes up when I'm testing.