[Dnsmasq-discuss] Reg: Info related to leases file

[Lonnie Abelbeck]

On Oct 3, 2013, at 8:05 AM, Nehal J Wani wrote:

>> Yes. I just added contrib/mactable/macscript to the git repo, which is your
>> previous script slightly less elegantly modified by me for this
>> circumstance. I also put back the "make new file then atomically rename"
>> behaviour since that means anything using this file doesn't risk a race
>> condition leading to a half-written file.
>> 
> 
> I gave a try to the --dhcp-script option of dnsmasq. Following are the findings:
> 
> Script used: (a little modified version of
> http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=blob_plain;f=contrib/mactable/macscript;hb=HEAD):
> 
> #!/bin/bash
> 
> STATUS_FILE="/var/lib/libvirt/
> dnsmasq/dnsmasq-ip-mac.status"
> 
> # Script for dnsmasq lease-change hook.
> # Maintains the above file with a IP address/MAC address pairs,
> # one lease per line. Works with IPv4 and IPv6 leases, file is
> # atomically updated, so no races for users of the data.
> 
> action="$1"
> mac="$2"   # IPv4
> ip="$3"
> 
> expirytime="$DNSMASQ_LEASE_EXPIRES"
> hostname="$DNSMASQ_SUPPLIED_HOSTNAME"
> clientid="$DNSMASQ_CLIENT_ID"
> 
> # ensure it always exists.
> 
> if [ ! -f "$STATUS_FILE" ]; then
>  touch "$STATUS_FILE"
> fi
> 
> if [  -n "$DNSMASQ_IAID" ]; then
>    mac="$DNSMASQ_MAC"   # IPv6
>    clientid="$2"
> fi
> 
> # worry about an add or old action when the MAC address is not known:
> # leave any old one in place in that case.
> 
> if [ "$action" = "add" -o "$action" = "old" -o "$action" = "del" ]; then
>  if [ -n "$mac" -o "$action" = "del" ]; then
>    sed "/^${ip//./\.} / d" "$STATUS_FILE" > "$STATUS_FILE".new
> 
>    if [ "$action" = "add" -o "$action" = "old" ]; then
>       echo "$expirytime $mac $ip $hostname $clientid" >> "$STATUS_FILE".new
>    fi
>    mv  "$STATUS_FILE".new "$STATUS_FILE" # atomic update.
>  fi
> fi

-- snip --
> -- 
> Nehal J Wani

Unrelated to your questions, you broke the script by not keeping the $ip as the first field in the status file.  The "$ip" is used as a unique index of sorts.

The simple fix would be to put $ip as the first output of your "echo" command, otherwise some regex work on the "sed" command is required to match $ip in the middle rather than at the beginning.

Lonnie