netdev - Re: [PATCH 1/4] kernel: time: Add current_nw

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Date:	Thu, 25 Feb 2016 15:15:07 +0530
From:	Deepa Dinamani <deepa.kernel@...il.com>
To:	YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>
Cc:	Linux Network Devel Mailing List <netdev@...r.kernel.org>,
	y2038@...ts.linaro.org, Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH 1/4] kernel: time: Add current_nw_timestamp() for network timestamps

>>  include/linux/ip.h     |  2 ++
>>  include/linux/time64.h |  3 +++
>>  kernel/time/time.c     | 26 ++++++++++++++++++++++++++
>>  3 files changed, 31 insertions(+)
>>
>> diff --git a/include/linux/ip.h b/include/linux/ip.h
>> index 492bc65..edf923e 100644
>> --- a/include/linux/ip.h
>> +++ b/include/linux/ip.h
>> @@ -34,4 +34,6 @@ static inline struct iphdr *ipip_hdr(const struct sk_buff *skb)
>>  {
>>       return (struct iphdr *)skb_transport_header(skb);
>>  }
>> +
>> +extern __be32 current_nw_timestamp(void);
>>  #endif       /* _LINUX_IP_H */
>> diff --git a/include/linux/time64.h b/include/linux/time64.h
>> index 367d5af..5b5db3b 100644
>> --- a/include/linux/time64.h
>> +++ b/include/linux/time64.h
>> @@ -35,6 +35,9 @@ struct itimerspec64 {
>>  #define NSEC_PER_SEC 1000000000L
>>  #define FSEC_PER_SEC 1000000000000000LL
>>
>> +#define SECONDS_PER_DAY      86400
>> +#define MSEC_PER_DAY (SECONDS_PER_DAY * MSEC_PER_SEC)
>> +
>>  /* Located here for timespec[64]_valid_strict */
>>  #define TIME64_MAX                   ((s64)~((u64)1 << 63))
>>  #define KTIME_MAX                    ((s64)~((u64)1 << 63))
>> diff --git a/kernel/time/time.c b/kernel/time/time.c
>> index 86751c6..6df15df 100644
>> --- a/kernel/time/time.c
>> +++ b/kernel/time/time.c
>> @@ -245,6 +245,32 @@ struct timespec current_fs_time(struct super_block *sb)
>>  EXPORT_SYMBOL(current_fs_time);
>>
>>  /*
>> + * current_nw_timestamp - Return network time
>> + *
>> + * Return milliseconds since midnight in network byte order.
>> + */
>> +__be32 current_nw_timestamp(void)
>> +{
>> +     u64 now;
>> +     u32 secs;
>> +     u32 msecs;
>> +     struct timespec64 ts;
>> +
>> +     ktime_get_ts64(&ts);
>> +
>> +     /* Get secs since midnight. */
>> +     now = div_u64_rem(ts.tv_sec, SECONDS_PER_DAY, &secs);
>> +     /* Convert to msecs. */
>> +     msecs = secs * MSEC_PER_SEC;
>> +     /* Convert nsec to msec. */
>> +     msecs += (u32)ts.tv_nsec/NSEC_PER_MSEC;
>> +
>> +     /* Convert to network byte order. */
>> +     return htons(msecs);
>> +}
>> +EXPORT_SYMBOL(current_nw_timestamp);
>> +
>> +/*
>>   * Convert jiffies to milliseconds and back.
>>   *
>>   * Avoid unnecessary multiplications/divisions in the
>>
>
> Since net/ipv4/* are the only users, it is enough to put
> it in under net/ipv4/.

time.c hosts functions that are used by individual subsystems like
current_fs_time() used by filesystems
(sometimes used by other subsystems also).

The network timestamp function is used for both source route ip option
and timestamp icmp messages.
So it makes it difficult for it to be owned by a single layer.
This is the reason it was chosen to include here.

Another option is to include it in the lowest layer its used:
af_inet.c. Is this what you were suggesting?

-Deepa