QFileSystemEngine: a file only exists if its link count is not 0

QFileSystemMetaData::fillFromStatBuf is used when filling in the results
from both stat() as well as fstat(). Obviously the file exists if it was
stat()ed but not necessarily so by fstat(): we could be operating on a
file descriptor referring to an unlinked file or an O_TMPFILE.

Change-Id: I8d96dea9955d4c749b99fffd14cd52a8c8dd9ca1
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

5 files changed, 21 insertions, 6 deletions

diff --git a/src/corelib/io/qfile.cpp b/src/corelib/io/qfile.cpp
index c7a06e49d5..af7ff74389 100644
--- a/src/corelib/io/qfile.cpp
+++ b/src/corelib/io/qfile.cpp
@@ -421,7 +421,7 @@ QFile::exists() const
     Q_D(const QFile);
     // 0x1000000 = QAbstractFileEngine::Refresh, forcing an update
     return (d->engine()->fileFlags(QAbstractFileEngine::FlagsMask
-                                    | QAbstractFileEngine::FileFlag(0x1000000)) & QAbstractFileEngine::ExistsFlag);
+                                    | QAbstractFileEngine::Refresh) & QAbstractFileEngine::ExistsFlag);
 }
 
 /*!
diff --git a/src/corelib/io/qfilesystemengine.cpp b/src/corelib/io/qfilesystemengine.cpp
index ccbcdb1037..f3205ae6e2 100644
--- a/src/corelib/io/qfilesystemengine.cpp
+++ b/src/corelib/io/qfilesystemengine.cpp
@@ -281,7 +281,9 @@ void QFileSystemMetaData::fillFromStatBuf(const QT_STATBUF &statBuffer)
         entryFlags |= QFileSystemMetaData::SequentialType;
 
     // Attributes
-    entryFlags |= QFileSystemMetaData::ExistsAttribute;
+    entryFlags |= QFileSystemMetaData::ExistsAttribute; // inode exists
+    if (statBuffer.st_nlink == 0)
+        entryFlags |= QFileSystemMetaData::WasDeletedAttribute;
     size_ = statBuffer.st_size;
 #if defined(Q_OS_DARWIN)
     if (statBuffer.st_flags & UF_HIDDEN) {
diff --git a/src/corelib/io/qfilesystemmetadata_p.h b/src/corelib/io/qfilesystemmetadata_p.h
index b09223d656..2f25721bee 100644
--- a/src/corelib/io/qfilesystemmetadata_p.h
+++ b/src/corelib/io/qfilesystemmetadata_p.h
@@ -120,9 +120,14 @@ public:
         // Attributes
         HiddenAttribute     = 0x00100000,
         SizeAttribute       = 0x00200000,   // Note: overlaps with QAbstractFileEngine::LocalDiskFlag
-        ExistsAttribute     = 0x00400000,
+        ExistsAttribute     = 0x00400000,   // For historical reasons, indicates existence of data, not the file
+#if defined(Q_OS_WIN)
+        WasDeletedAttribute =        0x0,
+#else
+        WasDeletedAttribute = 0x40000000,   // Indicates the file was deleted
+#endif
 
-        Attributes          = HiddenAttribute | SizeAttribute | ExistsAttribute,
+        Attributes          = HiddenAttribute | SizeAttribute | ExistsAttribute | WasDeletedAttribute,
 
         // Times
         CreationTime        = 0x01000000,   // Note: overlaps with QAbstractFileEngine::Refresh
@@ -144,6 +149,7 @@ public:
                             | QFileSystemMetaData::DirectoryType
                             | QFileSystemMetaData::SequentialType
                             | QFileSystemMetaData::SizeAttribute
+                            | QFileSystemMetaData::WasDeletedAttribute
                             | QFileSystemMetaData::Times
                             | QFileSystemMetaData::OwnerIds,
 
@@ -191,6 +197,7 @@ public:
     bool isLegacyLink() const               { return (entryFlags & LegacyLinkType); }
     bool isSequential() const               { return (entryFlags & SequentialType); }
     bool isHidden() const                   { return (entryFlags & HiddenAttribute); }
+    bool wasDeleted() const                 { return (entryFlags & WasDeletedAttribute); }
 #if defined(Q_OS_WIN)
     bool isLnkFile() const                  { return (entryFlags & WinLnkType); }
 #else
diff --git a/src/corelib/io/qfsfileengine_unix.cpp b/src/corelib/io/qfsfileengine_unix.cpp
index 69961ff76a..dadd5d9bcf 100644
--- a/src/corelib/io/qfsfileengine_unix.cpp
+++ b/src/corelib/io/qfsfileengine_unix.cpp
@@ -495,11 +495,14 @@ QAbstractFileEngine::FileFlags QFSFileEngine::fileFlags(FileFlags type) const
                     | QFileSystemMetaData::LinkType
                     | QFileSystemMetaData::FileType
                     | QFileSystemMetaData::DirectoryType
-                    | QFileSystemMetaData::BundleType;
+                    | QFileSystemMetaData::BundleType
+                    | QFileSystemMetaData::WasDeletedAttribute;
 
         if (type & FlagsMask)
             queryFlags |= QFileSystemMetaData::HiddenAttribute
                     | QFileSystemMetaData::ExistsAttribute;
+        else if (type & ExistsFlag)
+            queryFlags |= QFileSystemMetaData::WasDeletedAttribute;
 
         queryFlags |= QFileSystemMetaData::LinkType;
 
@@ -531,7 +534,8 @@ QAbstractFileEngine::FileFlags QFSFileEngine::fileFlags(FileFlags type) const
     }
 
     if (type & FlagsMask) {
-        if (exists)
+        // the inode existing does not mean the file exists
+        if (!d->metaData.wasDeleted())
             ret |= ExistsFlag;
         if (d->fileEntry.isRoot())
             ret |= RootFlag;
diff --git a/src/corelib/io/qfsfileengine_win.cpp b/src/corelib/io/qfsfileengine_win.cpp
index d749e32447..6d8db1a72e 100644
--- a/src/corelib/io/qfsfileengine_win.cpp
+++ b/src/corelib/io/qfsfileengine_win.cpp
@@ -741,6 +741,8 @@ QAbstractFileEngine::FileFlags QFSFileEngine::fileFlags(QAbstractFileEngine::Fil
     }
     if (type & FlagsMask) {
         if (d->metaData.exists()) {
+            // if we succeeded in querying, then the file exists: a file on
+            // Windows cannot be deleted if we have an open handle to it
             ret |= ExistsFlag;
             if (d->fileEntry.isRoot())
                 ret |= RootFlag;