• David Howells's avatar
    dns: Allow the dns resolver to retrieve a server set · bbb4c432
    David Howells authored
    Allow the DNS resolver to retrieve a set of servers and their associated
    addresses, ports, preference and weight ratings.
    In terms of communication with userspace, "srv=1" is added to the callout
    string (the '1' indicating the maximum data version supported by the
    kernel) to ask the userspace side for this.
    If the userspace side doesn't recognise it, it will ignore the option and
    return the usual text address list.
    If the userspace side does recognise it, it will return some binary data
    that begins with a zero byte that would cause the string parsers to give an
    error.  The second byte contains the version of the data in the blob (this
    may be between 1 and the version specified in the callout data).  The
    remainder of the payload is version-specific.
    In version 1, the payload looks like (note that this is packed):
    	u8	Non-string marker (ie. 0)
    	u8	Content (0 => Server list)
    	u8	Version (ie. 1)
    	u8	Source (eg. DNS_RECORD_FROM_DNS_SRV)
    	u8	Status (eg. DNS_LOOKUP_GOOD)
    	u8	Number of servers
    	foreach-server {
    		u16	Name length (LE)
    		u16	Priority (as per SRV record) (LE)
    		u16	Weight (as per SRV record) (LE)
    		u16	Port (LE)
    		u8	Source (eg. DNS_RECORD_FROM_NSS)
    		u8	Status (eg. DNS_LOOKUP_GOT_NOT_FOUND)
    		u8	Protocol (eg. DNS_SERVER_PROTOCOL_UDP)
    		u8	Number of addresses
    		char[]	Name (not NUL-terminated)
    		foreach-address {
    			u8		Family (AF_INET{,6})
    			union {
    				u8[4]	ipv4_addr
    				u8[16]	ipv6_addr
    This can then be used to fetch a whole cell's VL-server configuration for
    AFS, for example.
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
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