block/file-win32: add reopen handlers

Make 'qemu-img commit' work on Windows.

Command 'commit' requires reopening backing file in RW mode. So,
add reopen prepare/commit/abort handlers and change dwShareMode
for CreateFile call in order to allow further read/write reopening.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/418

Suggested-by: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Viktor Prutyanov <viktor.prutyanov@phystech.edu>
Tested-by: Helge Konetzka <hk@zapateado.de>
Message-Id: <20210825173625.19415-1-viktor.prutyanov@phystech.edu>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

block/file-win32.c

@@ -58,6 +58,10 @@ typedef struct BDRVRawState {
     QEMUWin32AIOState *aio;
 } BDRVRawState;
 
+typedef struct BDRVRawReopenState {
+    HANDLE hfile;
+} BDRVRawReopenState;
+
 /*
  * Read/writes the data to/from a given linear buffer.
  *
@@ -392,7 +396,7 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     s->hfile = CreateFile(filename, access_flags,
-                          FILE_SHARE_READ, NULL,
+                          FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
                           OPEN_EXISTING, overlapped, NULL);
     if (s->hfile == INVALID_HANDLE_VALUE) {
         int err = GetLastError();
@@ -634,6 +638,97 @@ static int coroutine_fn raw_co_create_opts(BlockDriver *drv,
     return raw_co_create(&options, errp);
 }
 
+static int raw_reopen_prepare(BDRVReopenState *state,
+                              BlockReopenQueue *queue, Error **errp)
+{
+    BDRVRawState *s = state->bs->opaque;
+    BDRVRawReopenState *rs;
+    int access_flags;
+    DWORD overlapped;
+    int ret = 0;
+
+    if (s->type != FTYPE_FILE) {
+        error_setg(errp, "Can only reopen files");
+        return -EINVAL;
+    }
+
+    rs = g_new0(BDRVRawReopenState, 1);
+
+    /*
+     * We do not support changing any options (only flags). By leaving
+     * all options in state->options, we tell the generic reopen code
+     * that we do not support changing any of them, so it will verify
+     * that their values did not change.
+     */
+
+    raw_parse_flags(state->flags, s->aio != NULL, &access_flags, &overlapped);
+    rs->hfile = CreateFile(state->bs->filename, access_flags,
+                           FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
+                           OPEN_EXISTING, overlapped, NULL);
+
+    if (rs->hfile == INVALID_HANDLE_VALUE) {
+        int err = GetLastError();
+
+        error_setg_win32(errp, err, "Could not reopen '%s'",
+                         state->bs->filename);
+        if (err == ERROR_ACCESS_DENIED) {
+            ret = -EACCES;
+        } else {
+            ret = -EINVAL;
+        }
+        goto fail;
+    }
+
+    if (s->aio) {
+        ret = win32_aio_attach(s->aio, rs->hfile);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Could not enable AIO");
+            CloseHandle(rs->hfile);
+            goto fail;
+        }
+    }
+
+    state->opaque = rs;
+
+    return 0;
+
+fail:
+    g_free(rs);
+    state->opaque = NULL;
+
+    return ret;
+}
+
+static void raw_reopen_commit(BDRVReopenState *state)
+{
+    BDRVRawState *s = state->bs->opaque;
+    BDRVRawReopenState *rs = state->opaque;
+
+    assert(rs != NULL);
+
+    CloseHandle(s->hfile);
+    s->hfile = rs->hfile;
+
+    g_free(rs);
+    state->opaque = NULL;
+}
+
+static void raw_reopen_abort(BDRVReopenState *state)
+{
+    BDRVRawReopenState *rs = state->opaque;
+
+    if (!rs) {
+        return;
+    }
+
+    if (rs->hfile != INVALID_HANDLE_VALUE) {
+        CloseHandle(rs->hfile);
+    }
+
+    g_free(rs);
+    state->opaque = NULL;
+}
+
 static QemuOptsList raw_create_opts = {
     .name = "raw-create-opts",
     .head = QTAILQ_HEAD_INITIALIZER(raw_create_opts.head),
@@ -659,6 +754,10 @@ BlockDriver bdrv_file = {
     .bdrv_co_create_opts = raw_co_create_opts,
     .bdrv_has_zero_init = bdrv_has_zero_init_1,
 
+    .bdrv_reopen_prepare = raw_reopen_prepare,
+    .bdrv_reopen_commit  = raw_reopen_commit,
+    .bdrv_reopen_abort   = raw_reopen_abort,
+
     .bdrv_aio_preadv    = raw_aio_preadv,
     .bdrv_aio_pwritev   = raw_aio_pwritev,
     .bdrv_aio_flush     = raw_aio_flush,