[Qemu-devel] [PATCH v2 for-2.7] wxx: Fix handling of files used for character devices

[Stefan Weil <sw@weilnetz.de>]

On Windows, such files were not truncated like on all other hosts.
Now we also test whether truncation is needed when running on Windows.

The append case was also incorrect because it needs a different value
for the desired access mode.

Reported-by: Benjamin David Lunt <fys@fysnet.net>
Signed-off-by: Stefan Weil <sw@weilnetz.de>
---

This patch supersedes my previous patch for qemu-char which only
fixed the truncate case. Paolo gave the hint to the wrong access mode
(see also commit 52074d0f662fc51293d4cde8077631f754784405).

Regards
Stefan

 qemu-char.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/qemu-char.c b/qemu-char.c
index e4b8448..e7d3399 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -4197,14 +4197,26 @@ static CharDriverState *qmp_chardev_open_file(const char *id,
     ChardevFile *file = backend->u.file.data;
     ChardevCommon *common = qapi_ChardevFile_base(file);
     HANDLE out;
+    DWORD accessmode;
+    DWORD flags;
 
     if (file->has_in) {
         error_setg(errp, "input file not supported");
         return NULL;
     }
 
-    out = CreateFile(file->out, GENERIC_WRITE, FILE_SHARE_READ, NULL,
-                     OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
+    if (file->has_append && file->append) {
+        /* Append to file if it already exists. */
+        accessmode = FILE_GENERIC_WRITE & ~FILE_WRITE_DATA;
+        flags = OPEN_ALWAYS;
+    } else {
+        /* Truncate file if it already exists. */
+        accessmode = GENERIC_WRITE;
+        flags = CREATE_ALWAYS;
+    }
+
+    out = CreateFile(file->out, accessmode, FILE_SHARE_READ, NULL, flags,
+                     FILE_ATTRIBUTE_NORMAL, NULL);
     if (out == INVALID_HANDLE_VALUE) {
         error_setg(errp, "open %s failed", file->out);
         return NULL;
-- 
2.1.4