syscallcompat: add Fstatat + emulation + test

Fstatat has recently been added to x/sys/unix. Make
it available for use in gocryptfs.

1 files changed, 10 insertions, 0 deletions

diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
index 0e03143..fb8d8b3 100644
--- a/internal/syscallcompat/sys_linux.go
+++ b/internal/syscallcompat/sys_linux.go
@@ -105,3 +105,13 @@ func Symlinkat(oldpath string, newdirfd int, newpath string) (err error) {
 func Mkdirat(dirfd int, path string, mode uint32) (err error) {
 	return syscall.Mkdirat(dirfd, path, mode)
 }
+
+// Fstatat syscall.
+func Fstatat(dirfd int, path string, stat *unix.Stat_t, flags int) (err error) {
+	// Why would we ever want to call this without AT_SYMLINK_NOFOLLOW?
+	if flags&unix.AT_SYMLINK_NOFOLLOW == 0 {
+		tlog.Warn.Printf("Fstatat: adding missing AT_SYMLINK_NOFOLLOW flag")
+		flags |= unix.AT_SYMLINK_NOFOLLOW
+	}
+	return unix.Fstatat(dirfd, path, stat, flags)
+}