[lxc-devel] [lxd/master] storage_cgo: make flag argument configurable

[brauner on Github]

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From 79a63c21b2f28971d61e2ea51ddd434f8049ed9a Mon Sep 17 00:00:00 2001
From: Christian Brauner <christian.brauner at ubuntu.com>
Date: Wed, 1 Mar 2017 02:24:27 +0100
Subject: [PATCH] storage_cgo: make flag argument configurable

For loop-backed btrfs pools we actually mount the loop device and so it's fine
to use LO_FLAGS_AUTOCLEAR since the loop device is guaranteed to be kept around
for as long as the mount exists. When we implement lvm loop-backed pools
however, we do not mount the loop device so we need to make sure that it is not
deconfigured automatically when we close all handles to it.

Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
---
 lxd/storage_btrfs.go |  5 ++++-
 lxd/storage_cgo.go   | 10 ++++++----
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/lxd/storage_btrfs.go b/lxd/storage_btrfs.go
index 7d62ae3..a69aac9 100644
--- a/lxd/storage_btrfs.go
+++ b/lxd/storage_btrfs.go
@@ -338,7 +338,10 @@ func (s *storageBtrfs) StoragePoolMount() (bool, error) {
 	mountSource := source
 	if filepath.IsAbs(source) {
 		if !shared.IsBlockdevPath(source) && s.d.BackingFs != "btrfs" {
-			loopF, err := prepareLoopDev(source)
+			// Since we mount the loop device LO_FLAGS_AUTOCLEAR is
+			// fine since the loop device will be kept around for as
+			// long as the mount exists.
+			loopF, err := prepareLoopDev(source, LO_FLAGS_AUTOCLEAR)
 			if err != nil {
 				return false, fmt.Errorf("Could not prepare loop device.")
 			}
diff --git a/lxd/storage_cgo.go b/lxd/storage_cgo.go
index 95ede6f..d7a6ba3 100644
--- a/lxd/storage_cgo.go
+++ b/lxd/storage_cgo.go
@@ -197,7 +197,7 @@ on_error:
 	return fd_tmp;
 }
 
-int prepare_loop_dev(const char *source, char *loop_dev)
+int prepare_loop_dev(const char *source, char *loop_dev, int flags)
 {
 	int ret;
 	struct loop_info64 lo64;
@@ -220,7 +220,7 @@ int prepare_loop_dev(const char *source, char *loop_dev)
 		goto on_error;
 
 	memset(&lo64, 0, sizeof(lo64));
-	lo64.lo_flags = LO_FLAGS_AUTOCLEAR;
+	lo64.lo_flags = flags;
 
 	ret = ioctl(fd_loop, LOOP_SET_STATUS64, &lo64);
 	if (ret < 0)
@@ -248,10 +248,12 @@ import (
 	"unsafe"
 )
 
+const LO_FLAGS_AUTOCLEAR int = C.LO_FLAGS_AUTOCLEAR
+
 // prepareLoopDev() detects and sets up a loop device for source. It returns an
 // open file descriptor to the free loop device and the path of the free loop
 // device. It's the callers responsibility to close the open file descriptor.
-func prepareLoopDev(source string) (*os.File, error) {
+func prepareLoopDev(source string, flags int) (*os.File, error) {
 	cLoopDev := C.malloc(C.size_t(C.LO_NAME_SIZE))
 	if cLoopDev == nil {
 		return nil, fmt.Errorf("Failed to allocate memory in C.")
@@ -265,7 +267,7 @@ func prepareLoopDev(source string) (*os.File, error) {
 		return os.NewFile(uintptr(loopFd), C.GoString((*C.char)(cLoopDev))), nil
 	}
 
-	loopFd, err := C.prepare_loop_dev(cSource, (*C.char)(cLoopDev))
+	loopFd, err := C.prepare_loop_dev(cSource, (*C.char)(cLoopDev), C.int(flags))
 	if loopFd < 0 {
 		if err != nil {
 			return nil, fmt.Errorf("Failed to prepare loop device: %s.", err)