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sd-dhcp-client: add RFC2131 retransmission details

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RFC2131, providing the details for dhcpv4, has specific retransmission
intervals that it outlines. This adds functions to compute the timeouts
as the RFC describes.
This commit is contained in:
Dan Streetman 2020-12-08 15:33:29 -05:00
parent 0c3c59783b
commit 3d75a443ee
1 changed files with 32 additions and 0 deletions
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32
src/libsystemd-network/sd-dhcp-client.c
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@ -29,6 +29,7 @@
#include "sort-util.h"
#include "string-util.h"
#include "strv.h"
#include "time-util.h"
#include "utf8.h"
#include "web-util.h"
@ -730,6 +731,37 @@ static void client_stop(sd_dhcp_client *client, int error) {
client_initialize(client);
}
/* RFC2131 section 4.1:
* retransmission delays should include -1 to +1 sec of random 'fuzz'. */
#define RFC2131_RANDOM_FUZZ \
((int64_t)(random_u64() % (2 * USEC_PER_SEC)) - (int64_t)USEC_PER_SEC)
/* RFC2131 section 4.1:
* for retransmission delays, timeout should start at 4s then double
* each attempt with max of 64s, with -1 to +1 sec of random 'fuzz' added.
* This assumes the first call will be using attempt 1. */
static usec_t client_compute_request_timeout(usec_t now, uint64_t attempt) {
usec_t timeout = (UINT64_C(1) << MIN(attempt + 1, UINT64_C(6))) * USEC_PER_SEC;
return usec_sub_signed(usec_add(now, timeout), RFC2131_RANDOM_FUZZ);
}
/* RFC2131 section 4.4.5:
* T1 defaults to (0.5 * duration_of_lease).
* T2 defaults to (0.875 * duration_of_lease). */
#define T1_DEFAULT(lifetime) ((lifetime) / 2)
#define T2_DEFAULT(lifetime) (((lifetime) * 7) / 8)
/* RFC2131 section 4.4.5:
* the client SHOULD wait one-half of the remaining time until T2 (in RENEWING state)
* and one-half of the remaining lease time (in REBINDING state), down to a minimum
* of 60 seconds.
* Note that while the default T1/T2 initial times do have random 'fuzz' applied,
* the RFC sec 4.4.5 does not mention adding any fuzz to retries. */
static usec_t client_compute_reacquisition_timeout(usec_t now, usec_t expire) {
return MAX(usec_sub_unsigned(expire, now) / 2, 60 * USEC_PER_SEC);
}
static int cmp_uint8(const uint8_t *a, const uint8_t *b) {
return CMP(*a, *b);
}