Revert "syscallcompat: drop Faccessat AT_SYMLINK_NOFOLLOW helper"

Breaks mounting on MacOS: unix.Faccessat on Darwin does NOT (yet)
support AT_SYMLINK_NOFOLLOW. See d44fe89ba4f3252c5bd00c4f7730197732f2a26a .

This reverts commit 0805a63df1b5f915b228727f6074c2506922d0ad.

1 files changed, 15 insertions, 0 deletions

diff --git a/internal/syscallcompat/sys_common.go b/internal/syscallcompat/sys_common.go
index aedc4da..b6bbdff 100644
--- a/internal/syscallcompat/sys_common.go
+++ b/internal/syscallcompat/sys_common.go
@@ -29,6 +29,21 @@ func Readlinkat(dirfd int, path string) (string, error) {
 	}
 }
 
+// Faccessat exists both in Linux and in MacOS 10.10+, but the Linux version
+// DOES NOT support any flags. Emulate AT_SYMLINK_NOFOLLOW like glibc does.
+func Faccessat(dirfd int, path string, mode uint32) error {
+	var st unix.Stat_t
+	err := Fstatat(dirfd, path, &st, unix.AT_SYMLINK_NOFOLLOW)
+	if err != nil {
+		return err
+	}
+	if st.Mode&syscall.S_IFMT == syscall.S_IFLNK {
+		// Pretend that a symlink is always accessible
+		return nil
+	}
+	return unix.Faccessat(dirfd, path, mode, 0)
+}
+
 // Openat wraps the Openat syscall.
 func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error) {
 	if flags&syscall.O_CREAT != 0 {