From: Xuzhou Cheng <xuzhou.ch...@windriver.com> The combination of GENERIC_WRITE and FILE_SHARE_READ options does not allow the same file to be opened again by CreateFile() from another QEMU process with the same options when the previous QEMU process still holds the file handle opened.
This was triggered by running the test_multifd_tcp_cancel() case on Windows, which cancels the migration, and launches another QEMU process to migrate with the same file opened for write. Chances are that the previous QEMU process does not quit before the new QEMU process runs hence the old one still holds the file handle that does not allow shared write permission then the new QEMU process will fail. There is another test case boot-serial-test that triggers the same issue. The qtest executable created a serial chardev file to be passed to the QEMU executable. The serial file was created by g_file_open_tmp(), which internally opens the file with FILE_SHARE_WRITE security attribute, and based on [1], there is only one case that allows the first call to CreateFile() with GENERIC_READ & FILE_SHARE_WRITE, and second call to CreateFile() with GENERIC_WRITE & FILE_SHARE_READ. All other combinations require FILE_SHARE_WRITE in the second call. But there is no way for the second call (in this case the QEMU executable) to know what combination was passed to the first call, so we will have to add FILE_SHARE_WRITE to the second call. For both scenarios we should add FILE_SHARE_WRITE in the chardev file backend driver. This change also makes the behavior to be consistent with the POSIX platforms. [1] https://docs.microsoft.com/en-us/windows/win32/fileio/creating-and-opening-files Signed-off-by: Xuzhou Cheng <xuzhou.ch...@windriver.com> Signed-off-by: Bin Meng <bin.m...@windriver.com> --- Changes in v3: - Add another case "boot-serial-test" to justify the change Changes in v2: - Update commit message to include the use case why we should set FILE_SHARE_WRITE when opening the file for win32 chardev/char-file.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/chardev/char-file.c b/chardev/char-file.c index 2fd80707e5..66385211eb 100644 --- a/chardev/char-file.c +++ b/chardev/char-file.c @@ -60,8 +60,8 @@ static void qmp_chardev_open_file(Chardev *chr, flags = CREATE_ALWAYS; } - out = CreateFile(file->out, accessmode, FILE_SHARE_READ, NULL, flags, - FILE_ATTRIBUTE_NORMAL, NULL); + out = CreateFile(file->out, accessmode, FILE_SHARE_READ | FILE_SHARE_WRITE, + NULL, flags, FILE_ATTRIBUTE_NORMAL, NULL); if (out == INVALID_HANDLE_VALUE) { error_setg(errp, "open %s failed", file->out); return; -- 2.34.1
