moveToTrash/Unix: use the file's inode number as collision avoidance

Instead of a sequential and thus predictable counter. This improves the
performance of when you keep creating and trashing the same file base
name. The previous algorithm would try all occurrences from 0 to however
many trashings have happened.

This could have been any random number, but the source file's inode is
"random" enough for us.

strace of the second file's trashing:

openat(AT_FDCWD, "/home/tjmaciei/.qttest/share/Trash/info/tst_qfile.moveToTrashOpenFile.vLwfNe.trashinfo", O_RDWR|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = -1 EEXIST (File exists)
newfstatat(AT_FDCWD, "/home/tjmaciei/tst_qfile.moveToTrashOpenFile.vLwfNe", {st_mode=S_IFREG|0644, st_size=16, ...}, 0) = 0
openat(AT_FDCWD, "/home/tjmaciei/.qttest/share/Trash/info/tst_qfile.moveToTrashOpenFile.vLwfNe-23527891.trashinfo", O_RDWR|O_CREAT|O_EXCL|O_CLOEXEC, 0666) = 4
newfstatat(AT_FDCWD, "/etc/localtime", {st_mode=S_IFREG|0644, st_size=2852, ...}, 0) = 0
write(4, "[Trash Info]\nPath=/home/tjmaciei"..., 103) = 103
renameat2(AT_FDCWD, "/home/tjmaciei/tst_qfile.moveToTrashOpenFile.vLwfNe", AT_FDCWD, "/home/tjmaciei/.qttest/share/Trash/files/tst_qfile.moveToTrashOpenFile.vLwfNe-23527891", RENAME_NOREPLACE) = 0
close(4)                                = 0

Change-Id: I9d43e5b91eb142d6945cfffd1786d73459c2eb3d
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 15 insertions, 4 deletions

diff --git a/src/corelib/io/qfilesystemengine_unix.cpp b/src/corelib/io/qfilesystemengine_unix.cpp
index 64ada6c83c..75c682d807 100644
--- a/src/corelib/io/qfilesystemengine_unix.cpp
+++ b/src/corelib/io/qfilesystemengine_unix.cpp
@@ -1418,14 +1418,25 @@ bool QFileSystemEngine::moveFileToTrash(const QFileSystemEntry &source,
     */
     QString uniqueTrashedName = u'/' + sourcePath.fileName();
     if (!op.tryCreateInfoFile(uniqueTrashedName, error) && error.errorCode == EEXIST) {
-        for (int counter = 0; op.infoFileFd == -1; ++counter) {
-            uniqueTrashedName = QString::asprintf("/%ls-%04d", qUtf16Printable(sourcePath.fileName()),
-                                                  counter);
+        // we'll use a counter, starting with the file's inode number to avoid
+        // collisions
+        qulonglong counter;
+        if (QT_STATBUF st; Q_LIKELY(QT_STAT(source.nativeFilePath(), &st) == 0)) {
+            counter = st.st_ino;
+        } else {
+            error = QSystemError(errno, QSystemError::StandardLibraryError);
+            return false;
+        }
+
+        QString uniqueTrashBase = std::move(uniqueTrashedName);
+        for (;;) {
+            uniqueTrashedName = QString::asprintf("%ls-%llu", qUtf16Printable(uniqueTrashBase),
+                                                  counter++);
             if (op.tryCreateInfoFile(uniqueTrashedName, error))
                 break;
             if (error.errorCode != EEXIST)
                 return false;
-          }
+        };
     }
 
     QByteArray info =