Hi

On Tue, Sep 20, 2022 at 2:33 PM Bin Meng <bmeng.cn@gmail.com> wrote:

> From: Xuzhou Cheng <xuzhou.cheng@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.
>
> As per [1] we should add FILE_SHARE_WRITE to the share mode to allow
> such use case. This change makes the behavior 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.cheng@windriver.com>
> Signed-off-by: Bin Meng <bin.meng@windriver.com>
> ---
>
> Changes in v2:
> - Update commit message to include the use case why we should set
>   FILE_SHARE_WRITE when openning the file for win32
>

As discussed in v1, I would rather leave that patch out of this series,
since the visible issue is solved differently elsewhere.

Also, I disagree with the approach to make windows behaviour consistent
with posix here, since I consider the windows behaviour (exclusive write
access) superior. I would rather teach the posix implementation about
exclusive write access.


>  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
>
>
>

-- 
Marc-André Lureau