diff --git a/download_action_unittest.cc b/download_action_unittest.cc
index 432cb16..be9d170 100644
--- a/download_action_unittest.cc
+++ b/download_action_unittest.cc
@@ -547,6 +547,12 @@
 };
 
 TEST_F(P2PDownloadActionTest, IsWrittenTo) {
+  if (!utils::IsXAttrSupported(FilePath("/tmp"))) {
+    LOG(WARNING) << "Skipping test because /tmp does not support xattr. "
+                 << "Please update your system to support this feature.";
+    return;
+  }
+
   SetupDownload(0);    // starting_offset
   StartDownload(true); // use_p2p_to_share
 
@@ -562,6 +568,12 @@
 }
 
 TEST_F(P2PDownloadActionTest, DeleteIfHoleExists) {
+  if (!utils::IsXAttrSupported(FilePath("/tmp"))) {
+    LOG(WARNING) << "Skipping test because /tmp does not support xattr. "
+                 << "Please update your system to support this feature.";
+    return;
+  }
+
   SetupDownload(1000); // starting_offset
   StartDownload(true); // use_p2p_to_share
 
@@ -572,6 +584,12 @@
 }
 
 TEST_F(P2PDownloadActionTest, CanAppend) {
+  if (!utils::IsXAttrSupported(FilePath("/tmp"))) {
+    LOG(WARNING) << "Skipping test because /tmp does not support xattr. "
+                 << "Please update your system to support this feature.";
+    return;
+  }
+
   SetupDownload(1000); // starting_offset
 
   // Prepare the file with existing data before starting to write to
@@ -601,6 +619,12 @@
 }
 
 TEST_F(P2PDownloadActionTest, DeletePartialP2PFileIfResumingWithoutP2P) {
+  if (!utils::IsXAttrSupported(FilePath("/tmp"))) {
+    LOG(WARNING) << "Skipping test because /tmp does not support xattr. "
+                 << "Please update your system to support this feature.";
+    return;
+  }
+
   SetupDownload(1000); // starting_offset
 
   // Prepare the file with all existing data before starting to write
diff --git a/p2p_manager.cc b/p2p_manager.cc
index 7536fc6..596adf1 100644
--- a/p2p_manager.cc
+++ b/p2p_manager.cc
@@ -606,18 +606,21 @@
                   FALLOC_FL_KEEP_SIZE, // Keep file size as 0.
                   0,
                   expected_size) != 0) {
-      // ENOSPC can happen (funky race though, cf. the statvfs() check
-      // above), handle it gracefully, e.g. use logging level INFO.
-      //
-      // NOTE: we *could* handle ENOSYS gracefully (ie. we could
-      // ignore it) but currently we don't because running out of
-      // space later sounds absolutely horrible. Better to fail fast.
-      PLOG(INFO) << "Error allocating " << expected_size
-                 << " bytes for file " << path.value();
-      if (unlink(path.value().c_str()) != 0) {
-        PLOG(ERROR) << "Error deleting file with path " << path.value();
+      if (errno == ENOSYS || errno == EOPNOTSUPP) {
+        // If the filesystem doesn't support the fallocate, keep
+        // going. This is helpful when running unit tests on build
+        // machines with ancient filesystems and/or OSes.
+        PLOG(WARNING) << "Ignoring fallocate(2) failure";
+      } else {
+        // ENOSPC can happen (funky race though, cf. the statvfs() check
+        // above), handle it gracefully, e.g. use logging level INFO.
+        PLOG(INFO) << "Error allocating " << expected_size
+                   << " bytes for file " << path.value();
+        if (unlink(path.value().c_str()) != 0) {
+          PLOG(ERROR) << "Error deleting file with path " << path.value();
+        }
+        return false;
       }
-      return false;
     }
 
     string decimal_size = StringPrintf("%zu", expected_size);
diff --git a/p2p_manager_unittest.cc b/p2p_manager_unittest.cc
index ce8d644..bee0248 100644
--- a/p2p_manager_unittest.cc
+++ b/p2p_manager_unittest.cc
@@ -287,6 +287,12 @@
 
 // Check that sharing a *new* file works.
 TEST_F(P2PManagerTest, ShareFile) {
+  if (!utils::IsXAttrSupported(FilePath("/tmp"))) {
+    LOG(WARNING) << "Skipping test because /tmp does not support xattr. "
+                 << "Please update your system to support this feature.";
+    return;
+  }
+
   scoped_ptr<P2PManager> manager(P2PManager::Construct(test_conf_,
                                                        NULL, "cros_au", 3));
   EXPECT_TRUE(manager->FileShare("foo", 10 * 1000 * 1000));
@@ -304,6 +310,12 @@
 
 // Check that making a shared file visible, does what is expected.
 TEST_F(P2PManagerTest, MakeFileVisible) {
+  if (!utils::IsXAttrSupported(FilePath("/tmp"))) {
+    LOG(WARNING) << "Skipping test because /tmp does not support xattr. "
+                 << "Please update your system to support this feature.";
+    return;
+  }
+
   scoped_ptr<P2PManager> manager(P2PManager::Construct(test_conf_,
                                                        NULL, "cros_au", 3));
   // First, check that it's not visible.
@@ -325,6 +337,12 @@
 
 // Check that we return the right values for existing files in P2P_DIR.
 TEST_F(P2PManagerTest, ExistingFiles) {
+  if (!utils::IsXAttrSupported(FilePath("/tmp"))) {
+    LOG(WARNING) << "Skipping test because /tmp does not support xattr. "
+                 << "Please update your system to support this feature.";
+    return;
+  }
+
   scoped_ptr<P2PManager> manager(P2PManager::Construct(test_conf_,
                                                        NULL, "cros_au", 3));
   bool visible;
diff --git a/utils.cc b/utils.cc
index cd7f384..c5d3e05 100644
--- a/utils.cc
+++ b/utils.cc
@@ -4,6 +4,7 @@
 
 #include "update_engine/utils.h"
 
+#include <attr/xattr.h>
 #include <sys/mount.h>
 #include <sys/resource.h>
 #include <sys/stat.h>
@@ -1067,6 +1068,36 @@
                       encoded_hash.c_str());
 }
 
+bool IsXAttrSupported(const base::FilePath& dir_path) {
+  char *path = strdup(dir_path.Append("xattr_test_XXXXXX").value().c_str());
+
+  int fd = mkstemp(path);
+  if (fd == -1) {
+    PLOG(ERROR) << "Error creating temporary file in " << dir_path.value();
+    free(path);
+    return false;
+  }
+
+  if (unlink(path) != 0) {
+    PLOG(ERROR) << "Error unlinking temporary file " << path;
+    close(fd);
+    free(path);
+    return false;
+  }
+
+  int xattr_res = fsetxattr(fd, "user.xattr-test", "value", strlen("value"), 0);
+  if (xattr_res != 0) {
+    if (errno == ENOTSUP) {
+      // Leave it to call-sites to warn about non-support.
+    } else {
+      PLOG(ERROR) << "Error setting xattr on " << path;
+    }
+  }
+  close(fd);
+  free(path);
+  return xattr_res == 0;
+}
+
 }  // namespace utils
 
 }  // namespace chromeos_update_engine
diff --git a/utils.h b/utils.h
index 2dd8095..6f6539f 100644
--- a/utils.h
+++ b/utils.h
@@ -12,6 +12,7 @@
 #include <unistd.h>
 #include <vector>
 
+#include <base/file_path.h>
 #include <base/posix/eintr_wrapper.h>
 #include <base/time.h>
 #include <ext2fs/ext2fs.h>
@@ -341,6 +342,11 @@
 // http://www.chromium.org/chromium-os/chromiumos-design-docs/disk-format
 bool GetInstallDev(const std::string& boot_dev, std::string* install_dev);
 
+// Checks if xattr is supported in the directory specified by
+// |dir_path| which must be writable. Returns true if the feature is
+// supported, false if not or if an error occured.
+bool IsXAttrSupported(const base::FilePath& dir_path);
+
 }  // namespace utils