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Currently we always keep the flow table maximally compact: that is all the active entries are contiguous at the start of the table. Doing this sometimes requires moving an entry when one is freed. That's kind of fiddly, and potentially expensive: it requires updating the hash table for the new location, and depending on flow type, it may require EPOLL_CTL_MOD, system calls to update epoll tags with the new location too. Implement a new way of managing the flow table that doesn't ever move entries. It attempts to maintain some compactness by always using the first free slot for a new connection, and mitigates the effect of non compactness by cheaply skipping over contiguous blocks of free entries. See the "theory of operation" comment in flow.c for details. Signed-off-by: David Gibson <david@gibson.dropbear.id.au>b [sbrivio: additional ASSERT(flow_first_free <= FLOW_MAX - 2) to avoid Coverity Scan false positive] Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
109 lines
2.6 KiB
C
109 lines
2.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later
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* Copyright Red Hat
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* Author: David Gibson <david@gibson.dropbear.id.au>
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*
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* Definitions for the global table of packet flows.
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*/
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#ifndef FLOW_TABLE_H
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#define FLOW_TABLE_H
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#include "tcp_conn.h"
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/**
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* struct flow_free_cluster - Information about a cluster of free entries
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* @f: Generic flow information
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* @n: Number of entries in the free cluster (including this one)
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* @next: Index of next free cluster
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*/
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struct flow_free_cluster {
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/* Must be first element */
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struct flow_common f;
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unsigned n;
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unsigned next;
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};
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/**
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* union flow - Descriptor for a logical packet flow (e.g. connection)
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* @f: Fields common between all variants
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* @tcp: Fields for non-spliced TCP connections
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* @tcp_splice: Fields for spliced TCP connections
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*/
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union flow {
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struct flow_common f;
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struct flow_free_cluster free;
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struct tcp_tap_conn tcp;
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struct tcp_splice_conn tcp_splice;
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};
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/* Global Flow Table */
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extern unsigned flow_first_free;
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extern union flow flowtab[];
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/** flow_idx - Index of flow from common structure
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* @f: Common flow fields pointer
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*
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* Return: index of @f in the flow table
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*/
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static inline unsigned flow_idx(const struct flow_common *f)
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{
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return (union flow *)f - flowtab;
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}
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/** FLOW_IDX - Find the index of a flow
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* @f_: Flow pointer, either union flow * or protocol specific
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*
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* Return: index of @f in the flow table
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*/
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#define FLOW_IDX(f_) (flow_idx(&(f_)->f))
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/** FLOW - Flow entry at a given index
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* @idx: Flow index
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*
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* Return: pointer to entry @idx in the flow table
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*/
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#define FLOW(idx) (&flowtab[(idx)])
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/** flow_at_sidx - Flow entry for a given sidx
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* @sidx: Flow & side index
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*
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* Return: pointer to the corresponding flow entry, or NULL
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*/
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static inline union flow *flow_at_sidx(flow_sidx_t sidx)
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{
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if (sidx.flow >= FLOW_MAX)
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return NULL;
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return FLOW(sidx.flow);
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}
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/** flow_sidx_t - Index of one side of a flow from common structure
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* @f: Common flow fields pointer
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* @side: Which side to refer to (0 or 1)
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*
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* Return: index of @f and @side in the flow table
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*/
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static inline flow_sidx_t flow_sidx(const struct flow_common *f,
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int side)
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{
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/* cppcheck-suppress [knownConditionTrueFalse, unmatchedSuppression] */
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ASSERT(side == !!side);
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return (flow_sidx_t){
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.side = side,
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.flow = flow_idx(f),
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};
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}
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/** FLOW_SIDX - Find the index of one side of a flow
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* @f_: Flow pointer, either union flow * or protocol specific
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* @side: Which side to index (0 or 1)
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*
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* Return: index of @f and @side in the flow table
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*/
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#define FLOW_SIDX(f_, side) (flow_sidx(&(f_)->f, (side)))
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union flow *flow_alloc(void);
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void flow_alloc_cancel(union flow *flow);
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#endif /* FLOW_TABLE_H */
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