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93295354df
Commit 0791315e4d (netlink-socket: Work around kernel Netlink dump thread races.) introduced a simple workaround for Linux kernel races in Netlink dumps. However, the code remained more complicated than needed. This commit simplifies it. The main reason for complication in the code was 'status_seq' in nl_dump. This member was there to allow a thread to wait for some other thread to refill the socket buffer with another dump message (although we did not understand the reason at the time it was introduced). Now that we know that Netlink dumps properly need to be serialized to work in existing Linux kernels, there's no additional value in having 'status_seq', because serialized recvmsg() calls always refill the socket buffer properly. This commit updates nl_msg_next() to clear its buffer argument on error. This is a more convenient interface for the new version of the Netlink dump code. nl_msg_next() doesn't have any other callers. Signed-off-by: Ben Pfaff <blp@nicira.com>
135 lines
4.9 KiB
C
135 lines
4.9 KiB
C
/*
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* Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014 Nicira, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef NETLINK_SOCKET_H
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#define NETLINK_SOCKET_H 1
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/* Netlink socket definitions.
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*
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* Netlink is a datagram-based network protocol primarily for communication
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* between user processes and the kernel, and mainly on Linux. Netlink is
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* specified in RFC 3549, "Linux Netlink as an IP Services Protocol".
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*
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* Netlink is not suitable for use in physical networks of heterogeneous
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* machines because host byte order is used throughout.
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*
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* This header file defines functions for working with Netlink sockets, which
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* are Linux-specific. For Netlink protocol definitions, see
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* netlink-protocol.h. For helper functions for working with Netlink messages,
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* see netlink.h.
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*
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*
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* Thread-safety
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* =============
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*
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* Most of the netlink functions are not fully thread-safe: Only a single
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* thread may use a given nl_sock or nl_dump at one time. The exceptions are:
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*
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* - nl_sock_recv() is conditionally thread-safe: it may be called from
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* different threads with the same nl_sock, but each caller must provide
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* an independent receive buffer.
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*
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* - nl_dump_next() is conditionally thread-safe: it may be called from
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* different threads with the same nl_dump, but each caller must provide
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* independent buffers.
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*/
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#include <stdbool.h>
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#include <stddef.h>
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#include <stdint.h>
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#include "ofpbuf.h"
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#include "ovs-atomic.h"
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#include "ovs-thread.h"
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struct nl_sock;
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#ifndef HAVE_NETLINK
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#error "netlink-socket.h is only for hosts that support Netlink sockets"
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#endif
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/* Netlink sockets. */
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int nl_sock_create(int protocol, struct nl_sock **);
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int nl_sock_clone(const struct nl_sock *, struct nl_sock **);
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void nl_sock_destroy(struct nl_sock *);
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int nl_sock_join_mcgroup(struct nl_sock *, unsigned int multicast_group);
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int nl_sock_leave_mcgroup(struct nl_sock *, unsigned int multicast_group);
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int nl_sock_send(struct nl_sock *, const struct ofpbuf *, bool wait);
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int nl_sock_send_seq(struct nl_sock *, const struct ofpbuf *,
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uint32_t nlmsg_seq, bool wait);
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int nl_sock_recv(struct nl_sock *, struct ofpbuf *, bool wait);
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int nl_sock_transact(struct nl_sock *, const struct ofpbuf *request,
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struct ofpbuf **replyp);
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int nl_sock_drain(struct nl_sock *);
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void nl_sock_wait(const struct nl_sock *, short int events);
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int nl_sock_fd(const struct nl_sock *);
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uint32_t nl_sock_pid(const struct nl_sock *);
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/* Batching transactions. */
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struct nl_transaction {
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/* Filled in by client. */
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struct ofpbuf *request; /* Request to send. */
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/* The client must initialize 'reply' to one of:
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*
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* - NULL, if it does not care to examine the reply.
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*
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* - Otherwise, to an ofpbuf with a memory allocation of at least
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* NLMSG_HDRLEN bytes.
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*/
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struct ofpbuf *reply; /* Reply (empty if reply was an error code). */
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int error; /* Positive errno value, 0 if no error. */
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};
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void nl_sock_transact_multiple(struct nl_sock *,
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struct nl_transaction **, size_t n);
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/* Transactions without an allocated socket. */
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int nl_transact(int protocol, const struct ofpbuf *request,
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struct ofpbuf **replyp);
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void nl_transact_multiple(int protocol, struct nl_transaction **, size_t n);
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/* Table dumping. */
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#define NL_DUMP_BUFSIZE 4096
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struct nl_dump {
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/* These members are immutable during the lifetime of the nl_dump. */
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struct nl_sock *sock; /* Socket being dumped. */
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uint32_t nl_seq; /* Expected nlmsg_seq for replies. */
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/* 'mutex' protects 'status' and serializes access to 'sock'. */
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struct ovs_mutex mutex; /* Protects 'status', synchronizes recv(). */
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int status OVS_GUARDED; /* 0: dump in progress,
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* positive errno: dump completed with error,
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* EOF: dump completed successfully. */
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};
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void nl_dump_start(struct nl_dump *, int protocol,
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const struct ofpbuf *request);
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bool nl_dump_next(struct nl_dump *, struct ofpbuf *reply, struct ofpbuf *buf);
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int nl_dump_done(struct nl_dump *);
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/* Miscellaneous */
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int nl_lookup_genl_family(const char *name, int *number);
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int nl_lookup_genl_mcgroup(const char *family_name, const char *group_name,
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unsigned int *multicast_group);
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#endif /* netlink-socket.h */
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