Add "Simple pread/pwrite" disk IO type

PR #21300.

src/base/bittorrent/session.h

@@ -92,7 +92,8 @@ namespace BitTorrent
         {
             Default = 0,
             MMap = 1,
-            Posix = 2
+            Posix = 2,
+            SimplePreadPwrite = 3
         };
         Q_ENUM_NS(DiskIOType)
 

src/base/bittorrent/sessionimpl.cpp

@@ -1638,6 +1638,13 @@ void SessionImpl::initializeNativeSession()
 #ifdef QBT_USES_LIBTORRENT2
     // preserve the same behavior as in earlier libtorrent versions
     pack.set_bool(lt::settings_pack::enable_set_file_valid_data, true);
+
+    // This is a special case. We use MMap disk IO but tweak it to always fallback to pread/pwrite.
+    if (diskIOType() == DiskIOType::SimplePreadPwrite)
+    {
+        pack.set_int(lt::settings_pack::mmap_file_size_cutoff, std::numeric_limits<int>::max());
+        pack.set_int(lt::settings_pack::disk_write_mode, lt::settings_pack::mmap_write_mode_t::always_pwrite);
+    }
 #endif
 
     lt::session_params sessionParams {std::move(pack), {}};
@@ -1648,6 +1655,7 @@ void SessionImpl::initializeNativeSession()
         sessionParams.disk_io_constructor = customPosixDiskIOConstructor;
         break;
     case DiskIOType::MMap:
+    case DiskIOType::SimplePreadPwrite:
         sessionParams.disk_io_constructor = customMMapDiskIOConstructor;
         break;
     default:

src/gui/advancedsettings.cpp

@@ -585,6 +585,7 @@ void AdvancedSettings::loadAdvancedSettings()
     m_comboBoxDiskIOType.addItem(tr("Default"), QVariant::fromValue(BitTorrent::DiskIOType::Default));
     m_comboBoxDiskIOType.addItem(tr("Memory mapped files"), QVariant::fromValue(BitTorrent::DiskIOType::MMap));
     m_comboBoxDiskIOType.addItem(tr("POSIX-compliant"), QVariant::fromValue(BitTorrent::DiskIOType::Posix));
+    m_comboBoxDiskIOType.addItem(tr("Simple pread/pwrite"), QVariant::fromValue(BitTorrent::DiskIOType::SimplePreadPwrite));
     m_comboBoxDiskIOType.setCurrentIndex(m_comboBoxDiskIOType.findData(QVariant::fromValue(session->diskIOType())));
     addRow(DISK_IO_TYPE, tr("Disk IO type (requires restart)") + u' ' + makeLink(u"https://www.libtorrent.org/single-page-ref.html#default-disk-io-constructor", u"(?)")
            , &m_comboBoxDiskIOType);

src/webui/www/private/views/preferences.html

@@ -1226,6 +1226,7 @@ Use ';' to split multiple entries. Can use wildcard '*'.)QBT_TR[CONTEXT=OptionsD
                         <option value="0">QBT_TR(Default)QBT_TR[CONTEXT=OptionsDialog]</option>
                         <option value="1">QBT_TR(Memory mapped files)QBT_TR[CONTEXT=OptionsDialog]</option>
                         <option value="2">QBT_TR(POSIX-compliant)QBT_TR[CONTEXT=OptionsDialog]</option>
+                        <option value="3">QBT_TR(Simple pread/pwrite)QBT_TR[CONTEXT=OptionsDialog]</option>
                     </select>
                 </td>
             </tr>