All,
Has there been any thought about adding SEEK_HOLE and SEEK_DATA (*)
support to Linux?
I ask primarily because of the interplay between 64-bit systems and
things like /var/log/lastlog (which appears as a 1.2TiB file due to
the nfsnobody UID of 4294967294).
(I'm realize that adding support for these additional seek() flags
wouldn't solve the problem ... archiving tools would still have to
implement it. And I can also hear the argument that Red Hat and other
distributions should re-implement lastlog handling to use a more modern
and efficient hashing/index format and perhaps that they should set
nfsnobody to "-1" ... I'd be curious if those details are driven by
some published standard or if they are artifacts of porting. I'd also
be curious what's happened with other 64-bit UNIX ports and whether
this issue ever came up in Linux ports to the Alpha or other 64-bit
processors).
As a stray data point I just did a quick experiment and just doing
a time cat /var/log/lastlog > /dev/null took about:
36.33user 2453.99system 41:35.90elapsed 99%CPU
(0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (133major+15minor)pagefaults 0swaps
On an otherwise idle 2GHz dual Opteron (yes, of course the extra
CPU is wasted for this job), reading SCSI disk hanging off a Fusion MPT
controller.
From what I hear our Networker processes pore over these NULs for about
two hours any time someone fails to exclude /var/log/lastlog from their
backup list.
* (see http://blogs.sun.com/roller/page/bonwick?entry=seek_hole_and_seek_data
for details)
(Please feel free to cc me on any responses, or I'll pick them up via
the archives and KT ... my account dropped off LKML years ago and I
don't want to punish my poor old IDSL line with the traffic now)
--
Jim Dennis
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