[PATCH v5 0/3] BOOTP/DHCPv4 enhancements

[seanedmond at linux.microsoft.com]

From: Sean Edmond <seanedmond at 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 v5:
- fix depends for BOOTP_RANDOM_XID:
  "depends on CMD_BOOTP && (LIB_RAND || LIB_HW_RAND)"
- add change log to individual patches

changes in v4:
- rebase master and resolve conflicts
- change commit description for DHCP option 209 patch (this is now
  an enhancement patch)
- 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: Additional fixes 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(-)

-- 
2.42.0