Re: [PATCH v4] block/file-win32: add reopen handlers

[Hanna Reitz <hreitz@redhat.com>]

On 25.08.21 01:48, Viktor Prutyanov wrote:
> 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>
> ---
>   v2:
>      - fix indentation in raw_reopen_prepare
>      - free rs if raw_reopen_prepare fails
>   v3:
>      - restore suggested-by field missed in v2
>   v4:
>      - add file type check
>      - add comment about options
>      - replace rs check with assert in raw_reopen_commit
>
>   block/file-win32.c | 100 ++++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 99 insertions(+), 1 deletion(-)
>
> diff --git a/block/file-win32.c b/block/file-win32.c
> index 2642088bd6..8320495f2b 100644
> --- a/block/file-win32.c
> +++ b/block/file-win32.c

[...]

> @@ -634,6 +638,96 @@ 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");
> +            goto fail;

I believe if we fail here, we’ve already opened rs->hfile, so we must 
close it or we’d leak it.

(Sorry I missed this in my v3 review :/)

Hanna

> +        }
> +    }
> +
> +    state->opaque = rs;
> +
> +    return 0;
> +
> +fail:
> +    g_free(rs);
> +    state->opaque = NULL;
> +
> +    return ret;
> +}