Re: [Qemu-devel] [PATCH v4 15/19] block: raw-win32 driver reopen support

[Jeff Cody <jcody@redhat.com>]

On 09/21/2012 04:43 AM, Paolo Bonzini wrote:
> Il 21/09/2012 10:33, Kevin Wolf ha scritto:
>>>> +    /* could not reopen the file handle, so fall back to opening
>>>> +     * new file (CreateFile) */
>>>> +    if (raw_s->hfile == INVALID_HANDLE_VALUE) {
>>>> +        raw_s->hfile = CreateFile(state->bs->filename, access_flags,
>>>> +                                  FILE_SHARE_READ, NULL, OPEN_EXISTING,
>>>> +                                  overlapped, NULL);
>>>> +        if (raw_s->hfile == INVALID_HANDLE_VALUE) {
>>>> +            /* this could happen because the access_flags requested are
>>>> +             * incompatible with the existing share mode of s->hfile,
>>>> +             * so our only option now is to close s->hfile, and try again.
>>>> +             * This could end badly */
>>>> +            CloseHandle(s->hfile);
>> How common is this case?
>>
>> We do have another option, namely not reopen at all and return an error.
>> Of course, this only makes sense if it doesn't mean that we almost never
>> succeed.
> 
> Probably pretty common since we specify FILE_SHARE_READ for the sharing
> mode, meaning that "subsequent open operations on a file or device are
> only able to request read access".
> 

Yes, I think this is by far the most common case.


> I would change it to FILE_SHARE_READ|FILE_SHARE_WRITE and remove this code.
> 
> Paolo
> 

I contemplated doing that, but I wasn't sure if there was any particular
reason it was originally done with FILE_SHARE_READ only in the first
place (security, etc..). I was hesitant to override that behaviour as
the new default under w32.  Do we know if this is acceptable / safe?