newnfs client and statfs

[Rick Macklem]

> On Sun, 1 May 2011, Rick Macklem wrote:
> 
> >> UINT64_MAX, etc., are defined in <sys/stdint.h>, which doesn't even
> >> need
> >> to be included explicitly, since it is (bogusly) standard namespace
> >> pollution in <sys/systm.h>. This namespace pollution gives the
> >> bizarre
> >> ...
> 
> > Ok, now I see them (in machine/include/_stdint.h). Appologies for
> > the
> > noise. I grep'd sys/sys and couldn't find anything called
> > (U)INT64_MAX.
> >
> > Now, remembering that sf_abytes is uint64_t per the RFCs, what do
> > people
> > think of either of these?
> >
> >  if (sfp->sf_abytes > INT64_MAX)
> >      sbp->f_bavail = INT64_MAX;
> >  else
> >      sbp->f_bavail = sfp->sf_abytes / NFS_FABLKSIZE;
> 
> You don't need to do anything at runtime, since everything is 64 bits
> and f_bavail is a block count while sf_abytes is a byte count. 1 bit
> is lost to the sign bit in f_bavail, but 9 bits are gained by scaling
> by NFS_FABLKSIZE, leaving 8 bits to spare.
> 
> Calculating the limit at runtime would give INT64_MAX /
> NFS_FABSBLKSIZE,
> or perhaps 1 more than that (to round up instead of down). You might
> still want to use an out-of-band limit like INT64_MAX for technical
> reasons, but that risks more bugs (for example, anything converting
> INT64_MAX / NFS_FABSBLKSIZE + 1 "back" to a byte count would overflow
> and anything converting INT64_MAX "back" to a byte count would
> overflow
> even uint64_t.
> 
> > Or should I try and do the division to see if the large
> > value in sf_abytes will fit in INT64_MAX after the division?
> > Something
> > like:
> 
> Runtime tests have the advantage of continuing to work if someone
> changes
> the types, provided they are robust, but making them robust is too
> hard
> here. Robust test's can't simply use INT64_MAX, since INT64_MAX is
> only
> the max if the type is int64_t...
> 
Ok, I realized the code in the last post was pretty bogus:-) My only
excuse was that I typed it as I was running out the door...

So, I played with it a bit and the attached patch seems to work for
i386. For the fields that are uint64_t in struct statfs, it just
divides/assigns. For the int64_t field that takes the divided value
(f_bavail) I did the division/assignment to a uint64_t tmp and then
assigned that to f_bavail. (Since any value that fits in uint64_t is
a positive value for int64_t after being divided by 2 or more, it will
always be positive.) For the other int64_t one, I just check for "> INT64_MAX"
and set it to INT64_MAX for that case, so it doesn't go negative.

Anyhow, the updated patch is attached and maybe kib@ can test it?

Thanks for the help with this. I realize I got rather confused during
the discussion, rick
-------------- next part --------------
A non-text attachment was scrubbed...
Name: statfs.patch
Type: text/x-patch
Size: 1315 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-fs/attachments/20110501/7a22f435/statfs.bin