[libc][fcntl] Simplify the handling of the return value from syscall … (llvm#96325)

Fixes llvm#95570

Author: simonzgx

libc/src/__support/OSUtil/linux/fcntl.cpp

@@ -67,15 +67,11 @@ int fcntl(int fd, int cmd, void *arg) {
   }
   case F_GETOWN: {
     struct f_owner_ex fex;
-    int retVal =
+    int ret =
         LIBC_NAMESPACE::syscall_impl<int>(SYS_fcntl, fd, F_GETOWN_EX, &fex);
-    if (retVal == -EINVAL)
-      return LIBC_NAMESPACE::syscall_impl<int>(SYS_fcntl, fd, cmd,
-                                               reinterpret_cast<void *>(arg));
-    if (static_cast<unsigned long>(retVal) <= -4096UL)
+    if (ret >= 0)
       return fex.type == F_OWNER_PGRP ? -fex.pid : fex.pid;
-
-    libc_errno = -retVal;
+    libc_errno = -ret;
     return -1;
   }
   // The general case

libc/test/src/fcntl/CMakeLists.txt

@@ -29,6 +29,7 @@ add_libc_unittest(
     libc.src.fcntl.fcntl
     libc.src.fcntl.open
     libc.src.unistd.close
+    libc.src.unistd.getpid
     libc.hdr.types.struct_flock
     libc.hdr.fcntl_macros
     libc.test.UnitTest.ErrnoSetterMatcher

libc/test/src/fcntl/fcntl_test.cpp

@@ -12,6 +12,7 @@
 #include "src/fcntl/fcntl.h"
 #include "src/fcntl/open.h"
 #include "src/unistd/close.h"
+#include "src/unistd/getpid.h"
 #include "test/UnitTest/ErrnoSetterMatcher.h"
 #include "test/UnitTest/Test.h"
 
@@ -163,3 +164,22 @@ TEST(LlvmLibcFcntlTest, UseAfterClose) {
   ASSERT_EQ(-1, LIBC_NAMESPACE::fcntl(fd, F_GETFL));
   ASSERT_ERRNO_EQ(EBADF);
 }
+
+TEST(LlvmLibcFcntlTest, SetGetOwnerTest) {
+  LIBC_NAMESPACE::libc_errno = 0;
+  using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Succeeds;
+  pid_t pid = LIBC_NAMESPACE::getpid();
+  ASSERT_GT(pid, -1);
+  constexpr const char *TEST_FILE_NAME = "testdata/fcntl_set_get_owner.test";
+  auto TEST_FILE = libc_make_test_file_path(TEST_FILE_NAME);
+  int fd = LIBC_NAMESPACE::open(TEST_FILE, O_CREAT | O_TRUNC | O_RDWR, S_IRWXU);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_GT(fd, 0);
+  int ret = LIBC_NAMESPACE::fcntl(fd, F_SETOWN, pid);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_GT(ret, -1);
+  int ret2 = LIBC_NAMESPACE::fcntl(fd, F_GETOWN);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_EQ(ret2, pid);
+  ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0));
+}