On Wed, 04 Aug 2010 15:16:33 +0100 David Howells wrote:
> From: Wang Lei <wang840925@xxxxxxxxx>
>
> See the added Documentation/networking/dns_resolver.txt for more information.
> ---
>
> Documentation/networking/dns_resolver.txt | 146 ++++++++++++++++++
> fs/cifs/Kconfig | 17 +-
> fs/cifs/cifsfs.c | 13 --
> fs/cifs/dns_resolve.c | 229 ++++++-----------------------
> fs/cifs/dns_resolve.h | 2
> include/keys/dns_resolver-type.h | 23 +++
> include/linux/dns_resolver.h | 34 ++++
> net/Kconfig | 1
> net/Makefile | 1
> net/dns_resolver/Kconfig | 27 +++
> net/dns_resolver/Makefile | 7 +
> net/dns_resolver/dns_key.c | 210 +++++++++++++++++++++++++++
> net/dns_resolver/dns_query.c | 159 ++++++++++++++++++++
> net/dns_resolver/internal.h | 44 ++++++
> 14 files changed, 708 insertions(+), 205 deletions(-)
> create mode 100644 Documentation/networking/dns_resolver.txt
> create mode 100644 include/keys/dns_resolver-type.h
> create mode 100644 include/linux/dns_resolver.h
> create mode 100644 net/dns_resolver/Kconfig
> create mode 100644 net/dns_resolver/Makefile
> create mode 100644 net/dns_resolver/dns_key.c
> create mode 100644 net/dns_resolver/dns_query.c
> create mode 100644 net/dns_resolver/internal.h
>
> diff --git a/Documentation/networking/dns_resolver.txt b/Documentation/networking/dns_resolver.txt
> new file mode 100644
> index 0000000..d8e0ce1
> --- /dev/null
> +++ b/Documentation/networking/dns_resolver.txt
> @@ -0,0 +1,146 @@
> + ===================
> + DNS Resolver Module
> + ===================
> +
> +Contents:
> +
> + - Overview.
> + - Compilation.
> + - Setting up.
> + - Usage.
> + - Mechanism.
> + - Debugging.
> +
> +
> +========
> +OVERVIEW
> +========
> +
> +The DNS resolver module provides a way for kernel services to make DNS queries
> +by way of requesting a key of key type dns_resolver. These queries are
> +upcalled to userspace through /sbin/request-key.
> +
> +These routines must be supported by userspace tools dns.upcall, cifs.upcall and
> +request-key. It is under development and does not yet provide the full feature
> +set. The features it does support include:
> +
> + (*) Implements the dns_resolver key_type to contact userspace.
> +
> +It does not yet support the following AFS features:
> +
> + (*) Dns query support for AFSDB resource record.
> +
> +This code is extracted from the CIFS filesystem.
> +
> +
> +===========
> +COMPILATION
> +===========
> +
> +The module should be enabled by turning on the kernel configuration options:
> +
> + CONFIG_DNS_RESOLVER - tristate "DNS Resolver support"
> +
> +
> +==========
> +SETTING UP
> +==========
> +
> +To set up this facility, the /etc/request-key.conf file must be altered so that
> +/sbin/request-key can appropriately direct the upcalls. For example, to handle
> +basic dname to IPv4/IPv6 address resolution, the following line should be
> +added:
> +
> + #OP TYPE DESC CO-INFO PROGRAM ARG1 ARG2 ARG3 ...
> + #====== ============ ======= ======= ==========================
> + create dns_resolver * * /usr/sbin/cifs.upcall %k
> +
> +To direct a query for query type 'foo', a line of the following should be added
> +before the more general line given above as the first match is the one taken.
> +
> + create dns_resolver foo:* * /usr/sbin/dns.foo %k
> +
> +
> +
> +=====
> +USAGE
> +=====
> +
> +To make use of this facility, one of the following functions that are
> +implemented in the module can be called after doing:
> +
> + #include <linux/dns_resolver.h>
> +
> + (1) int dns_query(const char *type, const char *name, size_t namelen,
> + const char *options, char **_result, time_t *_expiry);
> +
> + This is the basic access function. It looks for a cached DNS query and if
> + it doesn't find it, it upcalls to userspace to make a new DNS query, which
> + may then be cached. The key description is constructed as a string of the
> + form:
> +
> + [<type>:]<name>
> +
> + where <type> optionally specifies the particular upcall program to invoke,
> + and thus the type of query to do, and <name> specifies the string to be
> + looked up. The default query type is a straight hostname to IP address
> + set lookup.
> +
> + The name parameter is not required to be a NUL-terminated string, and its
> + length should be given by the namelen argument.
> +
> + The options parameter may be NULL or it may be a set of options
> + appropriate to the query type.
> +
> + The return value is a string appropriate to the query type. For instance,
> + for the default query type it is just a list of comma-separated IPv4 and
> + IPv6 addresses. The caller must free the result.
> +
> + The length of the result string is returned on success, and a -ve error
s/-ve/negative/ please. Some readers won't know that "-ve" means.
> + code is returned otherwise. -EKEYREJECTED will be returned if the DNS
> + lookup failed.
> +
> + If _expiry is non-NULL, the expiry time (TTL) of the result will be
> + returned also.
> +
> +
> +=========
> +MECHANISM
> +=========
> +
> +The dnsresolver module registers a key type called "dns_resolver". Keys of
> +this type are used to transport and cache DNS lookup results from userspace.
> +
> +When dns_query() is invoked, it calls request_key() to search the local
> +keyrings for a cached DNS result. If that fails to find one, it upcalls to
> +userspace to get a new result.
> +
> +Upcalls to userspace are made through the request_key() upcall vector, and are
> +directed by means of configuration lines in /etc/request-key.conf that tell
> +/sbin/request-key what program to run to instantiate the key.
> +
> +The upcall handler program is responsible for querying the DNS, processing the
> +result into a form suitable for passing to the keyctl_instantiate_key()
> +routine. This then passes the data to dns_resolver_instantiate() which strips
> +off and processes any options included in the data, and then attaches the
> +remainder of the string to the key as its payload.
> +
> +The upcall handler program should set the expiry time on the key to that of the
> +lowest TTL of all the records it has extracted a result from. This means that
> +the key will be discarded and recreated when the data it holds has expired.
> +
> +dns_query() returns a copy of the value attached to the key, or an error if
> +that is indicated instead.
> +
> +See <file:Documentation/keys-request-key.txt> for further information about
> +request-key function.
> +
> +
> +=========
> +DEBUGGING
> +=========
> +
> +Debugging messages can be turned on dynamically by writing a 1 into the
> +following file:
> +
> + /sys/module/dnsresolver/parameters/debug
> diff --git a/include/keys/dns_resolver-type.h b/include/keys/dns_resolver-type.h
> new file mode 100644
I sure would prefer not to mix - and _ in the file name.
> diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
> new file mode 100644
> index 0000000..6c0cf31
> --- /dev/null
> +++ b/net/dns_resolver/dns_query.c
> @@ -0,0 +1,159 @@
...
> +/*
Use
/**
to make this kernel-doc, since the lines below here already are that.
> + * dns_query - Query the DNS
> + * @type: Query type (or NULL for straight host->IP lookup)
> + * @name: Name to look up
> + * @namelen: Length of name
> + * @options: Request options (or NULL if no options)
> + * @_result: Where to place the returned data.
> + * @_expiry: Where to store the result expiry time (or NULL)
> + *
> + * The data will be returned in the pointer at *result, and the caller is
> + * responsible for freeing it.
> + *
> + * The description should be of the form "[<query_type>:]<domain_name>", and
> + * the options need to be appropriate for the query type requested. If no
> + * query_type is given, then the query is a straight hostname to IP address
> + * lookup.
> + *
> + * The DNS resolution lookup is performed by upcalling to userspace by way of
> + * requesting a key of type dns_resolver.
> + *
> + * Returns the size of the result on success, -ve error code otherwise.
> + */
> +int dns_query(const char *type, const char *name, size_t namelen,
> + const char *options, char **_result, time_t *_expiry)
> +{
---
~Randy
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