fix: an enquiry that reports an overflow has still answered

FILE_FS_VOLUME_INFORMATION ends in the volume's label, which is as long as the
label is. The buffer here held the fixed part and one character of it -- enough
for every field this reads, since the serial number precedes the label -- and
the object manager still reported STATUS_BUFFER_OVERFLOW because the label did
not fit. That value is 0x80000005: negative, so okw::ok said no, so the identity
position was left clear.

Which is a correct report of something that was not true. This implementation
was saying "this node's identity is not known here", a caller was believing it,
and the identity was sitting in the buffer.

It surfaced two packages away, in openkal-musl's probe on Windows: "two
different files have different identities" did not hold, because both had been
given the zero this branch leaves behind. The conformance suite could not have
said so and is right not to -- an implementation is allowed to decline the
field, so the suite reports the observation as one it did not make.

Room for a label is given so the ordinary case succeeds, and the overflow is
accepted so the extraordinary one still answers.

Author: Sunrisepeak

src/fs.cpp

@@ -173,14 +173,38 @@ int fill(void* h, kal_u32 wanted, kal_node_info* out) {
     // handle to something that is not on a volume --- the position is left
     // clear and a caller is told that this is not known, rather than being told
     // that two different nodes are the same.
+    // ⚠️⚠️ THE VOLUME ENQUIRY REPORTS AN OVERFLOW AND ANSWERS ANYWAY, AND
+    // TREATING THE OVERFLOW AS A FAILURE THREW THE ANSWER AWAY.
+    //
+    // FILE_FS_VOLUME_INFORMATION ends in the volume's LABEL, which is as long
+    // as the label is. A buffer holding the fixed part and one character of it
+    // is enough for every field this reads --- the serial number precedes the
+    // label --- and the object manager still reports STATUS_BUFFER_OVERFLOW,
+    // because the label did not fit. That value is 0x80000005: negative, so
+    // `okw::ok' said no, so the position was left clear.
+    //
+    // ⭐ WHICH IS A CORRECT REPORT OF SOMETHING THAT WAS NOT TRUE. The
+    // implementation was saying "this node's identity is not known here", a
+    // caller was believing it, and the identity was sitting in the buffer. It
+    // surfaced two packages away, in openkal-musl's probe: `two different files
+    // have different identities' did not hold on Windows, because both had been
+    // given the zero this branch leaves behind.
+    //
+    // Room for a label is given so the ordinary case SUCCEEDS, and the overflow
+    // is accepted so the extraordinary one still answers. Both are checked
+    // rather than one, because a label longer than this is a volume nobody
+    // tests with and the buffer would be back to reporting an overflow.
+    struct {
+        okw::file_fs_volume_information info;
+        wchar_t label_tail[128];
+    } volume{};
     okw::file_internal_information index{};
-    okw::file_fs_volume_information volume{};
     const long ri = okw::NtQueryInformationFile(h, &s, &index, sizeof index,
                                                 okw::file_internal_information_class);
     const long rv = okw::NtQueryVolumeInformationFile(h, &s, &volume, sizeof volume,
                                                       okw::fs_volume_information_class);
-    if (okw::ok(ri) && okw::ok(rv)) {
-        v.identity[0] = static_cast<kal_u64>(volume.serial_number);
+    if (okw::ok(ri) && (okw::ok(rv) || rv == okw::status_buffer_overflow)) {
+        v.identity[0] = static_cast<kal_u64>(volume.info.serial_number);
         v.identity[1] = static_cast<kal_u64>(index.index_number);
         v.present |= KAL_INFO_IDENTITY;
     }

src/win.h

@@ -215,6 +215,15 @@ __declspec(dllimport) unsigned long __stdcall RtlNtStatusToDosError(long status)
 
 inline bool ok(long status) { return status >= 0; }
 
+// ⚠️ AN ENQUIRY THAT REPORTS AN OVERFLOW HAS STILL ANSWERED. STATUS_BUFFER_OVERFLOW
+// is a warning rather than an error: the fixed part of the structure was written
+// and a variable-length tail was cut. `ok' correctly says no to it --- its sign
+// bit is set --- so a caller that reads only fields preceding the tail names it
+// here. Measured: `src/fs.cpp' read a volume serial number that the object
+// manager had written and discarded it, and two files two packages away were
+// reported to have the same identity.
+inline constexpr long status_buffer_overflow = static_cast<long>(0x80000005ul);
+
 // --- translation -------------------------------------------------------------
 //
 // The environment's error values are mapped onto the closed set the