On 30/06/14 10:39, Nehal J Wani wrote: > Hi! > > The man page of dnsmasq (under the section "-9, --leasefile-ro"), states: > When called like this the script should write the saved state of the > lease database, in dnsmasq leasefile format, to stdout and exit with > zero exit code. > > Q1. What is the purpose of printing to stdout? I guess it is for > dnsmasq to know the information of previous leases, but I am not sure.
Exactly that. Dnsmasq keeps a working copy of the lease database in memory, and it calls the lease script whenever this changes so that the lease-script can maintain the external copy in whatever non-volatile storage it wants (a database, disk file, NVRAM, etc). When dnsmasq first starts it has to copy the state of the lease database from the non-volatile storage to the in-memory copy. It does this by running the lease-script with the "init" method and the lease-script should dump the contents of the database. The reason the format is exactly the same as the lease-file and to stdout is that the whole thing can be done simply by replacing 'fopen(leasefile)' with 'popen(lease-script, "init")', the rest of the code is unchanged. > Q2. What all information do I need to print in 'dnsmasq leasefile > format' ? What is the exact format? Is there an example for this (like > the example file macscript)? The file starts with IPv4 leases, one per line. There are five fields on each line, seperated by spaces. Expiry time - decimal number, seconds since start of epoch MAC address - a hex "ARP type", followed by '-' followed by zero to 16 hex bytes, separated by ':'. If the ARP type is 1, for ethernet (this is most common) then the ARP type is skipped, UNLESS the MAC address in zero length. So 99-00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff 01- 00:11:22:33:44:55 are valid strings. IP address in dotted-quad format. Hostname, as specified in RFC 1123, para 2.1, or '*' if no hostname known. Client-id, up to 255 hex bytes separated by ':', or * if no client-id known. Next, if DHCPv6 is in use there may be a single line duid 00:11:22:33 which records the DUID used by the server. Max length of a duid is not specified in the standards, I think. dnsmasq limits it to 85 bytes. The longest defined DUID format is currently about 28 bytes, I think. If the duid line exists, then it will be followed by the DHCPv6 leases, one per line, five fields as for IPv4. The fields are different. Expiry time - same definition as for IPv4. IP address - in standard hex-and-colons format IAID Unsigned 32-bit decimal number, possibly preceded by "T" for a temporary lease. Hostname - same as IPv4 Client DUID - same representation as IPv4 client-ID. > Q3. Apart from the leases, dnsmasq also prints some extra information > like "duid 00:01:00:01:1b:40:8d:94:00:25:64:8b:e4:2c" in the lease > file. Is this also mandatory to print to stdout in case I use > leasefile-ro ? If you don't want to support DHCPv6, then you don't need the duid and the DHCPv6 lease format. It would be a pity not to support DHPCv6 though. Cheers, Simon. > > Thanking You, Happy to help with any of this. > Nehal J Wani > _______________________________________________ Dnsmasq-discuss mailing list Dnsmasqemail@example.com http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss