Merge pull request #40 from AkihiroSuda/drop-libbtrfs

Depend on kernel UAPI instead of libbtrfs; Bump up the package version to v2

.github/workflows/ci.yml

@@ -40,5 +40,9 @@ jobs:
     - name: Build
       working-directory: src/github.com/containerd/btrfs
       run: |
-        sudo apt-get update && sudo apt-get install -y libbtrfs-dev
         make vet binaries
+
+    - name: Build with an old version of kernel headers
+      working-directory: src/github.com/containerd/btrfs
+      run: |
+        DOCKER_BUILDKIT=1 docker build -f hack/Dockerfile.compilation-test .

README.md

@@ -11,6 +11,21 @@ Native Go bindings for btrfs.
 These are in the early stages. We will try to maintain stability, but please
 vendor if you are relying on these directly.
 
+# Dependencies
+
+## v2.x
+
+Headers from kernel 4.12 or newer.
+The package name is `linux-libc-dev` on Debian/Ubuntu, `kernel-headers` on Fedora and RHEL-like distros.
+
+The headers are only required on compilation time, not on run time.
+
+## v1.x
+
+libbtrfs headers.
+The package name is `libbtrfs-dev` on Debian/Ubuntu, `btrfs-progs-devel` on Fedora and CentOS 7.
+The package is not available for Rocky Linux and AlmaLinux.
+
 # Contribute
 
 This package may not cover all the use cases for btrfs. If something you need

btrfs.c

@@ -14,20 +14,16 @@
    limitations under the License.
 */
 
-#include <stddef.h>
-#include <linux/magic.h>
-#include <btrfs/ioctl.h>
-#include <btrfs/ctree.h>
-
+#include <string.h>
 #include "btrfs.h"
 
 void unpack_root_item(struct gosafe_btrfs_root_item* dst, struct btrfs_root_item* src) {
 	memcpy(dst->uuid, src->uuid, BTRFS_UUID_SIZE);
 	memcpy(dst->parent_uuid, src->parent_uuid, BTRFS_UUID_SIZE);
 	memcpy(dst->received_uuid, src->received_uuid, BTRFS_UUID_SIZE);
-	dst->gen = btrfs_root_generation(src);
-	dst->ogen = btrfs_root_otransid(src);
-	dst->flags = btrfs_root_flags(src);
+	dst->generation = src->generation;
+	dst->otransid = src->otransid;
+	dst->flags = src->flags;
 }
 
 /* unpack_root_ref(struct gosafe_btrfs_root_ref* dst, struct btrfs_root_ref* src) { */

btrfs.go

@@ -17,8 +17,7 @@
 package btrfs
 
 /*
-#include <stddef.h>
-#include <btrfs/ioctl.h>
+#include <linux/magic.h>
 #include "btrfs.h"
 
 static char* get_name_btrfs_ioctl_vol_args_v2(struct btrfs_ioctl_vol_args_v2* btrfs_struct) {
@@ -154,13 +153,13 @@ func subvolMap(path string) (map[uint64]*Info, error) {
 				// get an entry of the objectid, with name, but the parent is
 				// the offset.
 
-				nname := C.btrfs_stack_root_ref_name_len(&rr)
+				nname := le16ToNative(rr.name_len)
 				name := string(buf[C.sizeof_struct_btrfs_root_ref : C.sizeof_struct_btrfs_root_ref+uintptr(nname)])
 
 				info.ID = uint64(sh.objectid)
 				info.ParentID = uint64(sh.offset)
 				info.Name = name
-				info.DirID = uint64(C.btrfs_stack_root_ref_dirid(&rr))
+				info.DirID = le64ToNative(rr.dirid)
 
 				subvolsByID[uint64(sh.objectid)] = info
 			} else if sh._type == C.BTRFS_ROOT_ITEM_KEY &&
@@ -185,8 +184,8 @@ func subvolMap(path string) (map[uint64]*Info, error) {
 				info.ParentUUID = uuidString(&gri.parent_uuid)
 				info.ReceivedUUID = uuidString(&gri.received_uuid)
 
-				info.Generation = uint64(gri.gen)
-				info.OriginalGeneration = uint64(gri.ogen)
+				info.Generation = le64ToNative(gri.generation)
+				info.OriginalGeneration = le64ToNative(gri.otransid)
 
 				subvolsByID[uint64(sh.objectid)] = info
 			}

btrfs.h

@@ -14,23 +14,25 @@
    limitations under the License.
 */
 
-#include <stddef.h>
-#include <linux/magic.h>
-#include <btrfs/ioctl.h>
-#include <btrfs/ctree.h>
+#include <linux/version.h>
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4,12,0)
+#error "Headers from kernel >= 4.12 are required on compilation time (not on run time)"
+#endif
+#include <linux/btrfs.h>
+#include <linux/btrfs_tree.h>
 
 // unfortunately, we need to define "alignment safe" C structs to populate for
 // packed structs that aren't handled by cgo. Fields will be added here, as
 // needed.
 
 struct gosafe_btrfs_root_item {
-	u8 uuid[BTRFS_UUID_SIZE];
-	u8 parent_uuid[BTRFS_UUID_SIZE];
-	u8 received_uuid[BTRFS_UUID_SIZE];
+	__u8 uuid[BTRFS_UUID_SIZE];
+	__u8 parent_uuid[BTRFS_UUID_SIZE];
+	__u8 received_uuid[BTRFS_UUID_SIZE];
 
-	u64 gen;
-	u64 ogen;
-	u64 flags;
+	__le64 generation;
+	__le64 otransid;
+	__le64 flags;
 };
 
 void unpack_root_item(struct gosafe_btrfs_root_item* dst, struct btrfs_root_item* src);

cmd/btrfs-test/main.go

@@ -23,7 +23,7 @@ import (
 	"os"
 	"text/tabwriter"
 
-	"github.com/containerd/btrfs"
+	"github.com/containerd/btrfs/v2"
 )
 
 var (

go.mod

@@ -1,3 +1,5 @@
-module github.com/containerd/btrfs
+module github.com/containerd/btrfs/v2
 
 go 1.19
+
+require golang.org/x/sys v0.5.0

go.sum

@@ -0,0 +1,2 @@
+golang.org/x/sys v0.5.0 h1:MUK/U/4lj1t1oPg0HfuXDN/Z1wv31ZJ/YcPiGccS4DU=
+golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

hack/Dockerfile.compilation-test

@@ -0,0 +1,18 @@
+# Dockerfile for testing compilation with an old version of the kernel headers.
+
+ARG GOLANG_VERSION=1.19
+# LINUX_VERSION must be >= 4.12 (https://github.com/torvalds/linux/commit/fcc8487d477a3452a1d0ccbdd4c5e0e1e3cb8bed)
+ARG LINUX_VERSION=4.12
+
+FROM golang:${GOLANG_VERSION}
+ARG LINUX_VERSION
+RUN curl -sSL -O "https://mirrors.edge.kernel.org/pub/linux/kernel/v$(echo ${LINUX_VERSION} | cut -d. -f1).x/linux-${LINUX_VERSION}.tar.gz"
+RUN tar Cxzf / "linux-${LINUX_VERSION}.tar.gz" && \
+  cd "/linux-${LINUX_VERSION}" && \
+  make headers_install INSTALL_HDR_PATH=/usr2 && \
+  for f in /usr2/include/*; do rm -rf "/usr/include/$(basename ${f})"; done && \
+  cp -a /usr2/include /usr
+
+COPY . /go/src/github.com/containerd/btrfs
+WORKDIR /go/src/github.com/containerd/btrfs
+RUN make binaries

helpers.go

@@ -17,19 +17,20 @@
 package btrfs
 
 /*
-#include <stddef.h>
-#include <btrfs/ioctl.h>
-#include <btrfs/ctree.h>
+#include "btrfs.h"
 */
 import "C"
 
 import (
 	"bufio"
 	"bytes"
+	"encoding/binary"
 	"fmt"
 	"os"
 	"strings"
 	"unsafe"
+
+	"golang.org/x/sys/cpu"
 )
 
 func subvolID(fd uintptr) (uint64, error) {
@@ -48,7 +49,7 @@ var (
 	zeros     = zeroArray[:]
 )
 
-func uuidString(uuid *[C.BTRFS_UUID_SIZE]C.u8) string {
+func uuidString(uuid *[C.BTRFS_UUID_SIZE]C.__u8) string {
 	b := (*[maxByteSliceSize]byte)(unsafe.Pointer(uuid))[:C.BTRFS_UUID_SIZE]
 
 	if bytes.Equal(b, zeros) {
@@ -58,6 +59,24 @@ func uuidString(uuid *[C.BTRFS_UUID_SIZE]C.u8) string {
 	return fmt.Sprintf("%x-%x-%x-%x-%x", b[:4], b[4:4+2], b[6:6+2], b[8:8+2], b[10:16])
 }
 
+func le16ToNative(le16 C.__le16) uint16 {
+	if cpu.IsBigEndian {
+		b := make([]byte, 2)
+		binary.LittleEndian.PutUint16(b, uint16(le16))
+		return binary.BigEndian.Uint16(b)
+	}
+	return uint16(le16)
+}
+
+func le64ToNative(le64 C.__le64) uint64 {
+	if cpu.IsBigEndian {
+		b := make([]byte, 8)
+		binary.LittleEndian.PutUint64(b, uint64(le64))
+		return binary.BigEndian.Uint64(b)
+	}
+	return uint64(le64)
+}
+
 func findMountPoint(path string) (string, error) {
 	fp, err := os.Open("/proc/self/mounts")
 	if err != nil {