[PATCH v6 0/3] BOOTP/DHCPv4 enhancements

[Sean Edmond <seanedmond@microsoft.com>]

In our datacenter application, a single DHCP server is servicing 36000+ clients.
Improvements are required to the DHCPv4 retransmission behavior to align with
RFC and ensure less pressure is exerted on the server:
- retransmission backoff interval maximum is configurable
  (environment variable bootpretransmitperiodmax)
- initial retransmission backoff interval is configurable
  (environment variable bootpretransmitperiodinit)
- transaction ID is kept the same for each BOOTP/DHCPv4 request
  (not recreated on each retry)

For our application we'll use:
- bootpretransmitperiodmax=16000
- bootpretransmitperiodinit=2000

A new configuration BOOTP_RANDOM_XID has been added to enable a randomized
BOOTP/DHCPv4 transaction ID.

Enhance DHCPv4 sending/parsing option 209 (PXE config file).  A previous
patch was accepted.  A new patch fixes a possible double free() and
addresses latest review comments.

Changes in v6:
- CMD_BOOTP should "depends on LIB_RAND || LIB_HW_RAND"

Changes in v5:
- add change log to individual patches
- fix depends for BOOTP_RANDOM_XID:
  "depends on CMD_BOOTP && (LIB_RAND || LIB_HW_RAND)"

Changes in v4:
- rebase master and resolve conflicts
- default y for BOOTP_PXE_DHCP_OPTION (feedback from review)
- Add "select LIB_RAND" for "config CMD_BOOTP" (retransmission
  improvements require rand())

Changes in v3:
- add define for option 209 and rfc5071 reference
- Set RETRANSMIT_PERIOD_MAX_MS=60000
- Add randomization factor to retransmission timeout
- Add depends for BOOTP_RANDOM_XID

Changes in v2:
- use env_get_ulong() to get environment variables

Sean Edmond (3):
  net: Enhancements for dhcp option 209
  net: bootp: BOOTP/DHCPv4 retransmission improvements
  net: bootp: add config option BOOTP_RANDOM_XID

 cmd/Kconfig | 10 ++++++-
 cmd/pxe.c   |  2 ++
 net/bootp.c | 76 +++++++++++++++++++++++++++++++++++++++++------------
 net/bootp.h |  2 ++
 4 files changed, 72 insertions(+), 18 deletions(-)

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2.42.0