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

[Kevin Wolf <kwolf@redhat.com>]

Am 04.11.2021 um 15:20 hat Stefano Garzarella geschrieben:
> 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.

Yes, that's what it should be. Can be fixed up while applying. I had a
0/1/-errno return value in an intermediate version, which is how it
became 'int', but it's not necessary any more in this version.

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

Thanks!

Kevin