Initial implementation of file/inode flags (Linux, BSD, darwin)

Basic support for BSD and Darwin style chflags (stat flags). Applies
these flags at the end of file restore.
Supports linux style ioctl_iflags(2) in a 2 step process. Flags that
need to be applied prior to writes such as compress and especially no-COW
are applied immediately upon file open.

The flags format is backwards compatible. An attribute starting with a
null byte is used to store flags in the entry attributes table. With
an old version of duplicacy the restore of this attribute should silently
fail (effectively be ignored).

Fixes xattr restore to use O_NOFOLLOW so attributes are applied to symlink.

TODO: Tests, possible option to switch off mutable/append prior to
restore of existing file similar to rsync. Does not apply attributes
or flags to the top most directory.

src/duplicacy_utils_linux.go

@@ -0,0 +1,112 @@
+// Copyright (c) Acrosync LLC. All rights reserved.
+// Free for personal use and commercial trial
+// Commercial use requires per-user licenses available from https://duplicacy.com
+
+package duplicacy
+
+import (
+	"encoding/binary"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+const (
+	linux_FS_SECRM_FL        = 0x00000001 /* Secure deletion */
+	linux_FS_UNRM_FL         = 0x00000002 /* Undelete */
+	linux_FS_COMPR_FL        = 0x00000004 /* Compress file */
+	linux_FS_SYNC_FL         = 0x00000008 /* Synchronous updates */
+	linux_FS_IMMUTABLE_FL    = 0x00000010 /* Immutable file */
+	linux_FS_APPEND_FL       = 0x00000020 /* writes to file may only append */
+	linux_FS_NODUMP_FL       = 0x00000040 /* do not dump file */
+	linux_FS_NOATIME_FL      = 0x00000080 /* do not update atime */
+	linux_FS_NOCOMP_FL       = 0x00000400 /* Don't compress */
+	linux_FS_JOURNAL_DATA_FL = 0x00004000 /* Reserved for ext3 */
+	linux_FS_NOTAIL_FL       = 0x00008000 /* file tail should not be merged */
+	linux_FS_DIRSYNC_FL      = 0x00010000 /* dirsync behaviour (directories only) */
+	linux_FS_TOPDIR_FL       = 0x00020000 /* Top of directory hierarchies*/
+	linux_FS_NOCOW_FL        = 0x00800000 /* Do not cow file */
+	linux_FS_PROJINHERIT_FL  = 0x20000000 /* Create with parents projid */
+
+	linux_FS_IOC_GETFLAGS uintptr = 0x80086601
+	linux_FS_IOC_SETFLAGS uintptr = 0x40086602
+
+	linuxIocFlagsFileEarly = linux_FS_SECRM_FL | linux_FS_UNRM_FL | linux_FS_COMPR_FL | linux_FS_NODUMP_FL | linux_FS_NOATIME_FL | linux_FS_NOCOMP_FL | linux_FS_JOURNAL_DATA_FL | linux_FS_NOTAIL_FL | linux_FS_NOCOW_FL
+	linuxIocFlagsDirEarly  = linux_FS_TOPDIR_FL | linux_FS_PROJINHERIT_FL
+	linuxIocFlagsLate      = linux_FS_SYNC_FL | linux_FS_IMMUTABLE_FL | linux_FS_APPEND_FL | linux_FS_DIRSYNC_FL
+
+	linuxFileFlagsKey = "\x00lf"
+)
+
+func ioctl(f *os.File, request uintptr, attrp *uint32) error {
+	argp := uintptr(unsafe.Pointer(attrp))
+
+	if _, _, errno := syscall.Syscall(syscall.SYS_IOCTL, f.Fd(), request, argp); errno != 0 {
+		return os.NewSyscallError("ioctl", errno)
+	}
+	return nil
+}
+
+func (entry *Entry) ReadFileFlags(f *os.File) error {
+	var flags uint32
+	if err := ioctl(f, linux_FS_IOC_GETFLAGS, &flags); err != nil {
+		return err
+	}
+	if flags != 0 {
+		if entry.Attributes == nil {
+			entry.Attributes = &map[string][]byte{}
+		}
+		v := make([]byte, 4)
+		binary.LittleEndian.PutUint32(v, flags)
+		(*entry.Attributes)[linuxFileFlagsKey] = v
+		LOG_DEBUG("ATTR_READ", "Read flags 0x%x for %s", flags, entry.Path)
+	}
+	return nil
+}
+
+func (entry *Entry) RestoreEarlyDirFlags(path string) error {
+	if entry.Attributes == nil {
+		return nil
+	}
+	if v, have := (*entry.Attributes)[linuxFileFlagsKey]; have {
+		flags := binary.LittleEndian.Uint32(v) & linuxIocFlagsDirEarly
+		f, err := os.OpenFile(path, os.O_RDONLY|syscall.O_DIRECTORY, 0)
+		if err != nil {
+			return err
+		}
+		LOG_DEBUG("ATTR_RESTORE", "Restore dir flags (early) 0x%x for %s", flags, entry.Path)
+		err = ioctl(f, linux_FS_IOC_SETFLAGS, &flags)
+		f.Close()
+		return err
+	}
+	return nil
+}
+
+func (entry *Entry) RestoreEarlyFileFlags(f *os.File) error {
+	if entry.Attributes == nil {
+		return nil
+	}
+	if v, have := (*entry.Attributes)[linuxFileFlagsKey]; have {
+		flags := binary.LittleEndian.Uint32(v) & linuxIocFlagsFileEarly
+		LOG_DEBUG("ATTR_RESTORE", "Restore flags (early) 0x%x for %s", flags, entry.Path)
+		return ioctl(f, linux_FS_IOC_SETFLAGS, &flags)
+	}
+	return nil
+}
+
+func (entry *Entry) RestoreLateFileFlags(f *os.File) error {
+	if entry.Attributes == nil {
+		return nil
+	}
+	if v, have := (*entry.Attributes)[linuxFileFlagsKey]; have {
+		flags := binary.LittleEndian.Uint32(v) & (linuxIocFlagsFileEarly | linuxIocFlagsDirEarly | linuxIocFlagsLate)
+		LOG_DEBUG("ATTR_RESTORE", "Restore flags (late) 0x%x for %s", flags, entry.Path)
+		return ioctl(f, linux_FS_IOC_SETFLAGS, &flags)
+	}
+	return nil
+}
+
+func excludedByAttribute(attributes map[string][]byte) bool {
+	_, ok := attributes["user.duplicacy_exclude"]
+	return ok
+}