QSystemError: pass errno when calling stdString()

errno should be queried immediately after a libc function call fails,
calling it later on in QSystemError::stdString() may be too late.

Part of the goal of this, and similar, changes is removing the default
value of the stdString() method's parameter, to signify to users of that
method that errno should be stored ASAP if there is an error.

If there is any intervening code that may call a system/libc function
store errno in a local int var, otherwise use it directly in the
QSystemError::stdString() call, which takes by value.

Task-number: QTBUG-115199
Change-Id: If3f601a023ed0014e260089771220668dad88be8
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 12 insertions, 11 deletions

diff --git a/src/corelib/io/qfsfileengine.cpp b/src/corelib/io/qfsfileengine.cpp
index 2c86e85dd5..253e28cdd4 100644
--- a/src/corelib/io/qfsfileengine.cpp
+++ b/src/corelib/io/qfsfileengine.cpp
@@ -273,7 +273,7 @@ bool QFSFileEnginePrivate::openFh(QIODevice::OpenMode openMode, FILE *fh)
 
         if (ret != 0) {
             q->setError(errno == EMFILE ? QFile::ResourceError : QFile::OpenError,
-                        QSystemError::stdString());
+                        QSystemError::stdString(errno));
 
             this->openMode = QIODevice::NotOpen;
             this->fh = nullptr;
@@ -335,7 +335,7 @@ bool QFSFileEnginePrivate::openFd(QIODevice::OpenMode openMode, int fd)
 
         if (ret == -1) {
             q->setError(errno == EMFILE ? QFile::ResourceError : QFile::OpenError,
-                        QSystemError::stdString());
+                        QSystemError::stdString(errno));
 
             this->openMode = QIODevice::NotOpen;
             this->fd = -1;
@@ -394,7 +394,7 @@ bool QFSFileEnginePrivate::closeFdFh()
     if (!flushed || !closed) {
         if (flushed) {
             // If not flushed, we want the flush error to fall through.
-            q->setError(QFile::UnspecifiedError, QSystemError::stdString());
+            q->setError(QFile::UnspecifiedError, QSystemError::stdString(errno));
         }
         return false;
     }
@@ -446,7 +446,7 @@ bool QFSFileEnginePrivate::flushFh()
 
     if (ret != 0) {
         q->setError(errno == ENOSPC ? QFile::ResourceError : QFile::WriteError,
-                    QSystemError::stdString());
+                    QSystemError::stdString(errno));
         return false;
     }
     return true;
@@ -561,14 +561,14 @@ bool QFSFileEnginePrivate::seekFdFh(qint64 pos)
         } while (ret != 0 && errno == EINTR);
 
         if (ret != 0) {
-            q->setError(QFile::ReadError, QSystemError::stdString());
+            q->setError(QFile::ReadError, QSystemError::stdString(errno));
             return false;
         }
     } else {
         // Unbuffered stdio mode.
         if (QT_LSEEK(fd, QT_OFF_T(pos), SEEK_SET) == -1) {
+            q->setError(QFile::PositionError, QSystemError::stdString(errno));
             qWarning("QFile::at: Cannot set file position %lld", pos);
-            q->setError(QFile::PositionError, QSystemError::stdString());
             return false;
         }
     }
@@ -623,7 +623,7 @@ qint64 QFSFileEnginePrivate::readFdFh(char *data, qint64 len)
         size_t result;
         do {
             result = fread(data + readBytes, 1, size_t(len - readBytes), fh);
-            eof = feof(fh);
+            eof = feof(fh); // Doesn't change errno
             if (eof && result == 0) {
                 // On OS X, this is needed, e.g., if a file was written to
                 // through another stream since our last read. See test
@@ -654,7 +654,7 @@ qint64 QFSFileEnginePrivate::readFdFh(char *data, qint64 len)
 
     if (!eof && readBytes == 0) {
         readBytes = -1;
-        q->setError(QFile::ReadError, QSystemError::stdString());
+        q->setError(QFile::ReadError, QSystemError::stdString(errno));
     }
 
     return readBytes;
@@ -699,8 +699,8 @@ qint64 QFSFileEnginePrivate::readLineFdFh(char *data, qint64 maxlen)
     // does the same, so we'd get two '\0' at the end - passing maxlen + 1
     // solves this.
     if (!fgets(data, int(maxlen + 1), fh)) {
-        if (!feof(fh))
-            q->setError(QFile::ReadError, QSystemError::stdString());
+        if (!feof(fh)) // Doesn't change errno
+            q->setError(QFile::ReadError, QSystemError::stdString(errno));
         return -1;              // error
     }
 
@@ -777,7 +777,8 @@ qint64 QFSFileEnginePrivate::writeFdFh(const char *data, qint64 len)
 
     if (len &&  writtenBytes == 0) {
         writtenBytes = -1;
-        q->setError(errno == ENOSPC ? QFile::ResourceError : QFile::WriteError, QSystemError::stdString());
+        q->setError(errno == ENOSPC ? QFile::ResourceError : QFile::WriteError,
+                    QSystemError::stdString(errno));
     } else {
         // reset the cached size, if any
         metaData.clearFlags(QFileSystemMetaData::SizeAttribute);