Re: [PATCH] file-posix: Fix alignment after reopen changing O_DIRECT

[Stefano Garzarella]

On Thu, Nov 04, 2021 at 12:31:09PM +0100, Kevin Wolf wrote:
> At the end of a reopen, we already call bdrv_refresh_limits(), which
> should update bs->request_alignment according to the new file
> descriptor. However, raw_probe_alignment() relies on s->needs_alignment
> and just uses 1 if it isn't set. We neglected to update this field, so
> starting with cache=writeback and then reopening with cache=none means
> that we get an incorrect bs->request_alignment == 1 and unaligned
> requests fail instead of being automatically aligned.
>
> Fix this by recalculating s->needs_alignment in raw_refresh_limits()
> before calling raw_probe_alignment().
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
> block/file-posix.c         | 20 ++++++++++++++++----
> tests/qemu-iotests/142     | 22 ++++++++++++++++++++++
> tests/qemu-iotests/142.out | 15 +++++++++++++++
> 3 files changed, 53 insertions(+), 4 deletions(-)
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 7a27c83060..3f14e47096 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -167,6 +167,7 @@ typedef struct BDRVRawState {
>     int page_cache_inconsistent; /* errno from fdatasync failure */
>     bool has_fallocate;
>     bool needs_alignment;
> +    bool force_alignment;
>     bool drop_cache;
>     bool check_cache_dropped;
>     struct {
> @@ -351,6 +352,17 @@ static bool dio_byte_aligned(int fd)
>     return false;
> }
>
> +static int raw_needs_alignment(BlockDriverState *bs)

If you need to respin, maybe it's better to use `bool` as return type.

In both cases:
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

Stefano