Neil Brown wrote:
On Tue, 03 Aug 2010 11:53:07 -0400
Jason Keltz <jas@xxxxxxxxxxxx> wrote:
Hi.
Why is it that you cannot NFS export to a list of IPs and have exportfs
leave the list of IPs in etab without converting over to FQDN?
My memory is that if you only list IP addresses in /etc/exports then it will
do just want you want. But if you list any host names or net groups then it
has to do a DNS lookup on everything to see if either of those matches.
Hi Neil.
Thanks for your response!
Actually, if I list ONLY IPs in /etc/exports, and nothing else, then
etab gets converted over to using hostnames:
For example:
# cat /etc/exports
/test 130.63.92.24(ro,sync)
# cat /var/lib/nfs/etab
(it's empty)
# exportfs -a
# cat /var/lib/nfs/etab
/test
gold.cs.yorku.ca(ro,sync,wdelay,hide,nocrossmnt,secure,root_squash,no_all_squash,subtree_check,secure_locks,mapping=identity,anonuid=-2,anongid=-2)
In fact, I see two problems here. First, exportfs shouldn't convert
etab over to using FQDN. Second, if it does do this, I don't see why
rpc.mountd needs to RE-resolve each hostname in etab. During this
time (right after exportfs exits), all of my NFS shares hang, and an
strace of rpc.mountd shows that it is re-resolving all the hostnames
from etab. When it finishes, all activity continues. On one system
with a total of 30,000 hostnames listed, this ends up in a 30 second
hang time for all NFS exports! I was able to shrink this time slightly
by putting a caching name server on the NFS server, so that the NFS
server wasn't killing the DNS, but this didn't help enough. If exportfs
truly has to convert IPs over to hostname, I can live with that, but
then rpc.mountd shouldn't re-resolve the names. If both can live with
IPs, I'm good with that as well.
Now, albeit, I'm using an older nfs-utils that comes with RHEL4
installation. Compiling a later version is a bit tricky because some
libraries have changed. That being said, reviewing the source (given
that I don't really know it that well) for the newest nfs-utils, I don't
see how this behavior would really be any different. For example, in
client_lookup in support/export/client.c, adding some printfs, I can see
that the IPs always get into the ...
if (htype == MCL_FQDN && !canonical) {
... where there's a call to gethostbyname.
This is the same in nfs-utils-1.0.6 as it is in 1.2.2.
Why does mountd need to repeat the gethostbyname() lookup on every host
even though exportfs already converted over to using hostname?
exportfs doesn't convert over host hostnames. It essentially
copies /etc/exports to /var/lib/nfs/etab with minor formatting changes.
What do you actually put in /etc/exports, what do you find
in /var/lib/nfs/etab, and what exactly is the problem?
NeilBrown
See above.. thanks :)
Jason.
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