add getpreamblelen
add comments

sched: Fix tg_flags check with GROUP_FLAG_NOCLDWAIT

Approved-by: Gregory Nutt <gnutt@nuttx.org>

Jira: PDFW15IS-208
Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

Adds USB host support to stm32f411-disco board.

Approved-by: Gregory Nutt <gnutt@nuttx.org>

TUN driver: Implement TAP (OSI layer 2) mode.

Approved-by: Gregory Nutt <gnutt@nuttx.org>

Enable by setting the IFF_TAP flag instead of the IFF_TUN flag in ifr_flags.

libc/netdb: in dns_query_callback, ret != -EADDRNOTAVAIL condition consumes error returns including EAGAIN in this case, dns query retransmission doesn't work

Add logic to disable cancellation points within the OS.  This is useful when an internal OS function that is NOT a cancellation point calls an OS function which is a cancellation point.  In that case, irrecoverable states may occur if the cancellation is within the OS.