unix: add IoctlLoopConfigure on linux

LOOP_CONFIGURE ioctl is used to setup and configure all loop device
parameters in a single step.
Add to the unix package a new function that exposes LOOP_CONFIGURE.

Fixes golang/go#63962

Change-Id: Ia169d268b52b1384febc6bff9c707b721ab2bb24
GitHub-Last-Rev: f9cc4c9
GitHub-Pull-Request: #181
Reviewed-on: https://go-review.googlesource.com/c/sys/+/540075
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

Author: alex-matei

unix/ioctl_linux.go

@@ -231,3 +231,8 @@ func IoctlLoopGetStatus64(fd int) (*LoopInfo64, error) {
 func IoctlLoopSetStatus64(fd int, value *LoopInfo64) error {
 	return ioctlPtr(fd, LOOP_SET_STATUS64, unsafe.Pointer(value))
 }
+
+// IoctlLoopConfigure configures all loop device parameters in a single step
+func IoctlLoopConfigure(fd int, value *LoopConfig) error {
+	return ioctlPtr(fd, LOOP_CONFIGURE, unsafe.Pointer(value))
+}

unix/linux/types.go

@@ -3027,6 +3027,7 @@ const (
 
 type LoopInfo C.struct_loop_info
 type LoopInfo64 C.struct_loop_info64
+type LoopConfig C.struct_loop_config
 
 // AF_TIPC
 

unix/mkerrors.sh

@@ -519,6 +519,7 @@ ccflags="$@"
 		$2 ~ /^LOCK_(SH|EX|NB|UN)$/ ||
 		$2 ~ /^LO_(KEY|NAME)_SIZE$/ ||
 		$2 ~ /^LOOP_(CLR|CTL|GET|SET)_/ ||
+		$2 == "LOOP_CONFIGURE" ||
 		$2 ~ /^(AF|SOCK|SO|SOL|IPPROTO|IP|IPV6|TCP|MCAST|EVFILT|NOTE|SHUT|PROT|MAP|MREMAP|MFD|T?PACKET|MSG|SCM|MCL|DT|MADV|PR|LOCAL|TCPOPT|UDP)_/ ||
 		$2 ~ /^NFC_(GENL|PROTO|COMM|RF|SE|DIRECTION|LLCP|SOCKPROTO)_/ ||
 		$2 ~ /^NFC_.*_(MAX)?SIZE$/ ||