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

[Paolo Bonzini <pbonzini@redhat.com>]

On 02/08/2016 07:14, Stefan Weil wrote:
> 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;
> 

Matches the access mode and flags for qemu-ga.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks!