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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: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
33 lines
1.3 KiB
C
33 lines
1.3 KiB
C
/*
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* DNS Resolver upcall management for CIFS DFS and AFS
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* Handles host name to IP address resolution and DNS query for AFSDB RR.
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*
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* Copyright (c) International Business Machines Corp., 2008
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* Author(s): Steve French (sfrench@us.ibm.com)
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* Wang Lei (wang840925@gmail.com)
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*
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* This library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published
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* by the Free Software Foundation; either version 2.1 of the License, or
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* (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
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* the GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#ifndef _LINUX_DNS_RESOLVER_H
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#define _LINUX_DNS_RESOLVER_H
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#include <uapi/linux/dns_resolver.h>
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extern int dns_query(const char *type, const char *name, size_t namelen,
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const char *options, char **_result, time64_t *_expiry);
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#endif /* _LINUX_DNS_RESOLVER_H */
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