From 7ca82250e01cea6a270796beb2fa21de20b9b952 Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Wed, 2 Aug 2023 13:58:46 -0700
Subject: [PATCH] tst_QFile: update virtualFile() to check if readLine() reads
 all

We know that all lines from /proc/<PID>/maps end in a newline, so we
trim exactly that one byte, then we put it all back together with
.join('\n') to check if we've read the entire file.

Linux virtual files are usually served in 4 kB increments; tst_qfile's
maps file is about 16000 bytes for me, just short of the QIODevice buffer:

[pid 414315] read(5, "55c6afe04000-55c6afe11000 r--p 0"..., 16384) = 4049
[pid 414315] read(5, "7f215fd25000-7f215fd26000 r--p 0"..., 12335) = 4038
[pid 414315] read(5, "7f2160800000-7f21608c7000 r--p 0"..., 8297) = 4072
[pid 414315] read(5, "7f216119f000-7f21611a0000 rw-p 0"..., 4225) = 3994

It is not a coincidence that the reads are at line boundaries, though
it's not a guarantee from the kernel.

We appear to have accidentally fixed the QEMU emulation bug by reading
another process' /proc/<PID>/maps (hypothesis: QMU emulates the target
system in /proc/self, hiding itself in maps, but makes no translation
for other process map files.

Change-Id: Ifbf974a4d10745b099b1fffd1777ac919b12dc90
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
---
 tests/auto/corelib/io/qfile/tst_qfile.cpp | 50 ++++++++++++++++++-----
 1 file changed, 39 insertions(+), 11 deletions(-)

diff --git a/tests/auto/corelib/io/qfile/tst_qfile.cpp b/tests/auto/corelib/io/qfile/tst_qfile.cpp
index bd83aff141..1c53a2fa1b 100644
--- a/tests/auto/corelib/io/qfile/tst_qfile.cpp
+++ b/tests/auto/corelib/io/qfile/tst_qfile.cpp
@@ -52,7 +52,9 @@ QT_END_NAMESPACE
 #ifdef Q_OS_DARWIN
 # include <sys/mount.h>
 #elif defined(Q_OS_LINUX)
+# include <sys/eventfd.h>
 # include <sys/vfs.h>
+# include <sys/wait.h>
 #elif defined(Q_OS_FREEBSD)
 # include <sys/param.h>
 # include <sys/mount.h>
@@ -2613,8 +2615,29 @@ void tst_QFile::writeToReadOnlyFile()
 // This platform have 0-sized virtual files
 void tst_QFile::virtualFile()
 {
-    // test if QFile works with virtual files
-    QString fname = "/proc/self/maps";
+    // We need to test a large-ish /proc file on Linux, one that is usually
+    // over 4 kB (because the kernel writes in chunks of that), has a
+    // cross-platform file format, and is definitely readable. The best
+    // candidate and the one we can verify anything in is /proc/<PID>/maps.
+    // However, our act of reading may change the map because we allocate
+    // memory, so we fork() here so we have a frozen snapshot of the file.
+
+    int efd = eventfd(0, EFD_CLOEXEC);
+    pid_t pid = fork();
+    if (pid == 0) {
+        // child
+        uint64_t val;
+        eventfd_read(efd, &val);
+        _exit(0);
+    }
+    QVERIFY2(pid > 0, "fork failed: " + qt_error_string().toLocal8Bit());
+    auto waitForChild = qScopeGuard([=] {
+        eventfd_write(efd, 1);
+        close(efd);
+        waitpid(pid, nullptr, 0);
+    });
+
+    QString fname = u"/proc/%1/maps"_s.arg(pid);
 
     // consistency check
     QFileInfo fi(fname);
@@ -2625,11 +2648,7 @@ void tst_QFile::virtualFile()
     // open the file
     QFile f(fname);
     QVERIFY2(f.open(QIODevice::ReadOnly), msgOpenFailed(f).constData());
-    if (QTestPrivate::isRunningArmOnX86())
-        QEXPECT_FAIL("","QEMU does not read /proc/self/maps size correctly", Continue);
     QCOMPARE(f.size(), Q_INT64_C(0));
-    if (QTestPrivate::isRunningArmOnX86())
-        QEXPECT_FAIL("","QEMU does not read /proc/self/maps size correctly", Continue);
     QVERIFY(f.atEnd());
 
     // read data
@@ -2637,18 +2656,27 @@ void tst_QFile::virtualFile()
     QCOMPARE(data.size(), 16);
     QCOMPARE(f.pos(), Q_INT64_C(16));
 
+    // seeking
+    QVERIFY(f.seek(1));
+    QCOMPARE(f.pos(), Q_INT64_C(1));
+    QVERIFY(f.seek(0));
+    QCOMPARE(f.pos(), Q_INT64_C(0));
+
     // line-reading
-    data = f.readLine();
-    QVERIFY(!data.isEmpty());
+    QList<QByteArray> lines;
+    for (data = f.readLine(); !data.isEmpty(); data = f.readLine()) {
+        // chop the newline -- not using .trimmed() so cut exactly one byte
+        data.chop(1);
+        lines += std::move(data);
+    }
 
     // read all:
+    QVERIFY(f.seek(0));
     data = f.readAll();
     QVERIFY(f.pos() != 0);
     QVERIFY(!data.isEmpty());
 
-    // seeking
-    QVERIFY(f.seek(1));
-    QCOMPARE(f.pos(), Q_INT64_C(1));
+    QCOMPARE(data, lines.join('\n') + '\n');
 }
 #endif // defined(Q_OS_LINUX) || defined(Q_OS_AIX) || defined(Q_OS_FREEBSD) || defined(Q_OS_NETBSD)