QIODevice::readAll: allow reading from a huge non-sequential devices

On 32-bit systems, the non-sequential device could be pointing to a
device of 2 GB or more in size. If so, we should allow reading up to
the limit (2 GB - overhead), like we do for sequential devices in the
block above.

It could also happen on 64-bit systems, but the chance that you do have
a file bigger than 8 EB is remote.

[ChangeLog][QtCore][QIODevice] Changed readAll() handling of large
non-sequential devices like files that are bigger than the maximum
QByteArray size (on 32-bit systems, just under 2 GB). Previously,
readAll() always returned empty; now it will attempt to read from the
device.

Task-number: QTBUG-100546
Pick-to: 6.3
Change-Id: I74249c52dc02478ba93cfffd16d1a14ac92c77bb
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

1 files changed, 4 insertions, 3 deletions

diff --git a/src/corelib/io/qiodevice.cpp b/src/corelib/io/qiodevice.cpp
index bd1eaf11ce..978c6f2486 100644
--- a/src/corelib/io/qiodevice.cpp
+++ b/src/corelib/io/qiodevice.cpp
@@ -1261,7 +1261,9 @@ QByteArray QIODevice::read(qint64 maxSize)
 
     This function has no way of reporting errors; returning an empty
     QByteArray can mean either that no data was currently available
-    for reading, or that an error occurred.
+    for reading, or that an error occurred. This function also has no
+    way of indicating that more data may have been available and
+    couldn't be read.
 */
 QByteArray QIODevice::readAll()
 {
@@ -1295,10 +1297,9 @@ QByteArray QIODevice::readAll()
         } while (readResult > 0);
     } else {
         // Read it all in one go.
-        // If resize fails, don't read anything.
         readBytes -= d->pos;
         if (readBytes >= MaxByteArraySize)
-            return QByteArray();
+            readBytes = MaxByteArraySize;
         result.resize(readBytes);
         readBytes = d->read(result.data(), readBytes);
     }