sys_vfs_test: fix expectation for Linux 6.7.

I'd assumed that it was _deliberate_ that filesystems like procfs
reported 0 here, but apparently not. Good news: this makes for a more
worthwhile test than we had previously (at least when run on a 6.7+
kernel).

(This is the sys_vfs_test equivalent of the earlier change made to
sys_statvfs_test.)

Bug: http://b/321880382 (for sys_vfs_test)
Bug: http://b/319590754 (for sys_statvfs_test)
Test: treehugger
Change-Id: I3c6f784d1e348bf1be3a102d1dd6336c33d0b2db
(cherry picked from commit 1b48afbc66ada52a74e2c0d22ca50e377ced30f2)

1 files changed, 13 insertions, 2 deletions

diff --git a/tests/sys_vfs_test.cpp b/tests/sys_vfs_test.cpp
index 242f8d499..363e49bc5 100644
--- a/tests/sys_vfs_test.cpp
+++ b/tests/sys_vfs_test.cpp
@@ -28,10 +28,21 @@ template <typename StatFsT> void Check(StatFsT& sb) {
   EXPECT_EQ(4096, static_cast<int>(sb.f_bsize));
   EXPECT_EQ(0U, sb.f_bfree);
   EXPECT_EQ(0U, sb.f_ffree);
-  EXPECT_EQ(0, sb.f_fsid.__val[0]);
-  EXPECT_EQ(0, sb.f_fsid.__val[1]);
   EXPECT_EQ(255, static_cast<int>(sb.f_namelen));
 
+  // Linux 6.7 requires that all filesystems have a non-zero fsid.
+  if (sb.f_fsid.__val[0] != 0U) {
+    // fs/libfs.c reuses the filesystem's device number.
+    struct stat proc_sb;
+    ASSERT_EQ(0, stat("/proc", &proc_sb));
+    EXPECT_EQ(static_cast<int>(proc_sb.st_dev), sb.f_fsid.__val[0]);
+    EXPECT_EQ(0, sb.f_fsid.__val[1]);
+  } else {
+    // Prior to that, the fsid for /proc was just 0.
+    EXPECT_EQ(0, sb.f_fsid.__val[0]);
+    EXPECT_EQ(0, sb.f_fsid.__val[1]);
+  }
+
   // The kernel sets a private bit to indicate that f_flags is valid.
   // This flag is not supposed to be exposed to libc clients.
   static const uint32_t ST_VALID = 0x0020;