Enhanced __fxstata to handle AT_SYMLINK_NOFOLLOW

This patch also effectively makes unmodified coreutils
find work as expected:

./scripts/manifest_from_host.sh -w find && ./scripts/build fs=rofs --append-manifest
./scripts/run.py -e '/find / -ls'

Signed-off-by: Waldemar Kozaczuk <jwkozaczuk@gmail.com>
Message-Id: <20190519230604.11837-1-jwkozaczuk@gmail.com>

fs/vfs/main.cc

@@ -592,10 +592,6 @@ extern "C"
 int __fxstatat(int ver, int dirfd, const char *pathname, struct stat *st,
         int flags)
 {
-    if (flags & AT_SYMLINK_NOFOLLOW) {
-        UNIMPLEMENTED("fstatat() with AT_SYMLINK_NOFOLLOW");
-    }
-
     if (pathname[0] == '/' || dirfd == AT_FDCWD) {
         return stat(pathname, st);
     }
@@ -623,7 +619,12 @@ int __fxstatat(int ver, int dirfd, const char *pathname, struct stat *st,
     strlcat(p, "/", PATH_MAX);
     strlcat(p, pathname, PATH_MAX);
 
-    error = stat(p, st);
+    if (flags & AT_SYMLINK_NOFOLLOW) {
+        error = lstat(p, st);
+    }
+    else {
+        error = stat(p, st);
+    }
 
     vn_unlock(vp);
     fdrop(fp);

tests/tst-fstatat.cc

@@ -46,6 +46,7 @@ int main(int argc, char **argv)
     expect(fstatat(-1, "/tmp/f1", &st, 0), 0);
     expect(st.st_size, (off_t)0);
     expect_errno(fstatat(-1, "/tmp/f2", &st, 0), ENOENT);
+    expect_errno(fstatat(-1, "/tmp/f2", &st, AT_SYMLINK_NOFOLLOW), ENOENT);
 
     // test paths relative to cwd:
     char* oldwd = getcwd(NULL, 0);
@@ -54,6 +55,7 @@ int main(int argc, char **argv)
     expect(fstatat(AT_FDCWD, "f1", &st, 0), 0);
     expect(st.st_size, (off_t)0);
     expect_errno(fstatat(AT_FDCWD, "f2", &st, 0), ENOENT);
+    expect_errno(fstatat(AT_FDCWD, "f2", &st, AT_SYMLINK_NOFOLLOW), ENOENT);
 
     // test paths relative to open directory:
     chdir("/");
@@ -63,17 +65,25 @@ int main(int argc, char **argv)
     expect(fstatat(dir, "f1", &st, 0), 0);
     expect(st.st_size, (off_t)0);
     expect_errno(fstatat(dir, "f2", &st, 0), ENOENT);
+    expect_errno(fstatat(dir, "f2", &st, AT_SYMLINK_NOFOLLOW), ENOENT);
     close(dir);
 
     // test operating on an open file itself (not a directory)
     expect((dir = open("/tmp/f1", 0, O_PATH)) >= 0, true);
     st.st_size = 123;
     expect(fstatat(dir, "", &st, AT_EMPTY_PATH), 0);
     expect(st.st_size, (off_t)0);
-    close(dir);
 
+    // test AT_SYMLINK_NOFOLLOW with actual symlink
+    expect(symlink("/tmp/f1", "/tmp/symlink"), 0);
+    expect((dir = open("/tmp", 0, O_DIRECTORY)) >= 0, true);
+    expect(fstatat(dir, "symlink", &st, AT_SYMLINK_NOFOLLOW), 0);
+    expect(S_ISLNK(st.st_mode) != 0, true);
+
+    close(dir);
     chdir(oldwd);
     free(oldwd);
+    remove("/tmp/symlink");
     remove("/tmp/f1");
 
     std::cout << "SUMMARY: " << tests << " tests, " << fails << " failures\n";