netdev - Re: [PATCH] rtnetlink.7: Document struct ifa

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Message-ID: <xfzcwmn6syhywvdcu6kn3mkuwqpo5usiwkssblvk6qrpoys5dp@hwgvspb43tdo>
Date: Tue, 5 Nov 2024 12:33:48 +0100
From: Alejandro Colomar <alx@...nel.org>
To: Kuniyuki Iwashima <kuniyu@...zon.com>, alexhenrie24@...il.com, 
	branden@...ian.org
Cc: linux-man@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] rtnetlink.7: Document struct ifa_cacheinfo

Hi Alex, Kuniyuki, Branden,

On Mon, Nov 04, 2024 at 09:53:38PM GMT, Kuniyuki Iwashima wrote:
> From: Alex Henrie <alexhenrie24@...il.com>
> Date: Mon,  4 Nov 2024 21:14:20 -0700
> > struct ifa_cacheinfo contains the address's creation time, update time,
> > preferred lifetime, and valid lifetime. See

We use two spaces after period (the correct amount).  :)
(I'm thinking we probably want to document something about it in
 man-pages(7).  Branden, do you want to send a patch about it?  I want
 to include the references you showed to me, and you probably remember
 better those links.)

> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/if_addr.h?h=v6.11#n60

Please use this format for links:

Link: <http://example.com>

> > 
> > Signed-off-by: Alex Henrie <alexhenrie24@...il.com>
> > ---
> >  man/man7/rtnetlink.7 | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/man/man7/rtnetlink.7 b/man/man7/rtnetlink.7
> > index 86ed459bb..b05654315 100644
> > --- a/man/man7/rtnetlink.7
> > +++ b/man/man7/rtnetlink.7
> > @@ -176,7 +176,15 @@ IFA_BROADCAST:raw protocol address:broadcast address
> >  IFA_ANYCAST:raw protocol address:anycast address
> >  IFA_CACHEINFO:struct ifa_cacheinfo:Address information
> >  .TE
> > -.\" FIXME Document struct ifa_cacheinfo
> > +.IP
> > +.EX

Which include provides the structure?

> > +struct ifa_cacheinfo {
> > +    __u32 ifa_prefered; /* Preferred lifetime in seconds, -1 = forever */
> > +    __u32 ifa_valid;    /* Valid lifetime in seconds, -1 = forever */
> 
> -1 should be rather 0xFFFFFFFF (INFINITY_LIFE_TIME) as it's unsigned.

I prefer UINT32_MAX over 0xF...F, which might be unclear how many Fs it
has.

> Also, it would be nice to mention that ifa_prefered must be less than
> or equal to ifa_valid (ifa_prefered <= ifa_valid) and 0 is invalid for
> ifa_valid.
> 
>   0 <= ifa_prefered <= ifa_valid
>   0 < ifa_valid <= 0xFFFFFFFF

You may want to use interval notation, like we do in timespec(3type).

     struct timespec {
         time_t     tv_sec;   /* Seconds */
         /* ... */  tv_nsec;  /* Nanoseconds [0, 999'999'999] */
     };

It might also be interesting to add a separate manual page for the type,
and reference it here.  Otherwise, the page starts getting fatty.

Have a lovely day!
Alex

> 
> 
> > +    __u32 cstamp;       /* Creation timestamp in hundredths of seconds */
> > +    __u32 tstamp;       /* Update timestamp in hundredths of seconds */
> > +};
> 
> Maybe the explanation can follow the struct here as sentences.
> 
> 
> > +.EE
> >  .TP
> >  .B RTM_NEWROUTE
> >  .TQ
> > -- 
> > 2.47.0
> 

-- 
<https://www.alejandro-colomar.es/>

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