From ae0d0c9e7699f403970579277e77d747f9c61091 Mon Sep 17 00:00:00 2001
From: Elliott Hughes <enh@google.com>
Date: Wed, 21 Feb 2024 18:58:24 +0000
Subject: [PATCH] Clarify _PC_REC_INCR_XFER_SIZE and _PC_REC_MAX_XFER_SIZE.

The -1 from pathconf()/fpathconf() with these isn't the "I don't know
what you're talking about" -1/EINVAL, but the "I understand the
question, but don't have an answer for you --- you'll have to try it and
see" -1.

Bug: http://b/326245682
Test: treehugger
Change-Id: I67be277f3ffd9b5a355787ae7ffc4a31e32b0128
---
 libc/bionic/pathconf.cpp | 19 +++++++------------
 tests/unistd_test.cpp    | 40 +++++++++++++++++++++++++++-------------
 2 files changed, 34 insertions(+), 25 deletions(-)

diff --git a/libc/bionic/pathconf.cpp b/libc/bionic/pathconf.cpp
index 9724f4436..9bbecc36f 100644
--- a/libc/bionic/pathconf.cpp
+++ b/libc/bionic/pathconf.cpp
@@ -107,14 +107,6 @@ static long __pathconf(const struct statfs& s, int name) {
     case _PC_REC_MIN_XFER_SIZE:
       return s.f_bsize;
 
-#if 0
-    case _PC_REC_INCR_XFER_SIZE:
-    case _PC_REC_MAX_XFER_SIZE:
-#endif
-
-    case _PC_SYMLINK_MAX:
-      return -1; /* no limit */
-
     case _PC_CHOWN_RESTRICTED:
       return _POSIX_CHOWN_RESTRICTED;
 
@@ -125,12 +117,15 @@ static long __pathconf(const struct statfs& s, int name) {
       return _POSIX_VDISABLE;
 
     case _PC_ASYNC_IO:
-      return -1;
-
     case _PC_PRIO_IO:
-      return -1;
-
+    case _PC_REC_INCR_XFER_SIZE:
+    case _PC_REC_MAX_XFER_SIZE:
+    case _PC_SYMLINK_MAX:
     case _PC_SYNC_IO:
+      // No API to answer these: the caller will have to "try it and see".
+      // This differs from the next case in not setting errno to EINVAL,
+      // since we did understand the question --- we just don't have a
+      // good answer.
       return -1;
 
     default:
diff --git a/tests/unistd_test.cpp b/tests/unistd_test.cpp
index 88f5851c1..6c08972e6 100644
--- a/tests/unistd_test.cpp
+++ b/tests/unistd_test.cpp
@@ -753,22 +753,36 @@ TEST(UNISTD_TEST, gethostname) {
 
 TEST(UNISTD_TEST, pathconf_fpathconf) {
   TemporaryFile tf;
-  long rc = 0L;
+  long l;
+
   // As a file system's block size is always power of 2, the configure values
   // for ALLOC and XFER should be power of 2 as well.
-  rc = pathconf(tf.path, _PC_ALLOC_SIZE_MIN);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
-  rc = pathconf(tf.path, _PC_REC_MIN_XFER_SIZE);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
-  rc = pathconf(tf.path, _PC_REC_XFER_ALIGN);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
+  l = pathconf(tf.path, _PC_ALLOC_SIZE_MIN);
+  ASSERT_TRUE(l > 0 && powerof2(l));
+  l = pathconf(tf.path, _PC_REC_MIN_XFER_SIZE);
+  ASSERT_TRUE(l > 0 && powerof2(l));
+  l = pathconf(tf.path, _PC_REC_XFER_ALIGN);
+  ASSERT_TRUE(l > 0 && powerof2(l));
 
-  rc = fpathconf(tf.fd, _PC_ALLOC_SIZE_MIN);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
-  rc = fpathconf(tf.fd, _PC_REC_MIN_XFER_SIZE);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
-  rc = fpathconf(tf.fd, _PC_REC_XFER_ALIGN);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
+  l = fpathconf(tf.fd, _PC_ALLOC_SIZE_MIN);
+  ASSERT_TRUE(l > 0 && powerof2(l));
+  l = fpathconf(tf.fd, _PC_REC_MIN_XFER_SIZE);
+  ASSERT_TRUE(l > 0 && powerof2(l));
+  l = fpathconf(tf.fd, _PC_REC_XFER_ALIGN);
+  ASSERT_TRUE(l > 0 && powerof2(l));
+
+  // Check that the "I can't answer that, you'll have to try it and see"
+  // cases don't set errno.
+  int names[] = {
+      _PC_ASYNC_IO, _PC_PRIO_IO, _PC_REC_INCR_XFER_SIZE, _PC_REC_MAX_XFER_SIZE, _PC_SYMLINK_MAX,
+      _PC_SYNC_IO,  -1};
+  for (size_t i = 0; names[i] != -1; i++) {
+    errno = 0;
+    ASSERT_EQ(-1, pathconf(tf.path, names[i])) << names[i];
+    ASSERT_ERRNO(0) << names[i];
+    ASSERT_EQ(-1, fpathconf(tf.fd, names[i])) << names[i];
+    ASSERT_ERRNO(0) << names[i];
+  }
 }
 
 TEST(UNISTD_TEST, _POSIX_constants) {