On 25/05/2016 06:37, Eric Blake wrote:
> Similar to commit df7b97ff, we are mishandling clients that
> give an unaligned NBD_CMD_TRIM request, and potentially
> trimming bytes that occur before their request; which in turn
> can cause potential unintended data loss (unlikely in
> practice, since most clients are sane and issue aligned trim
> requests). However, while we fixed read and write by switching
> to the byte interfaces of blk_, we don't yet have a byte
> interface for discard. On the other hand, trim is advisory, so
> rounding the user's request to simply ignore the first and last
> unaligned sectors (or the entire request, if it is sub-sector
> in length) is just fine.
>
> CC: qemu-sta...@nongnu.org
> Signed-off-by: Eric Blake <ebl...@redhat.com>
> ---
> nbd/server.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/nbd/server.c b/nbd/server.c
> index fa862cd..5aed8db 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -1153,8 +1153,12 @@ static void nbd_trip(void *opaque)
> break;
> case NBD_CMD_TRIM:
> TRACE("Request type is TRIM");
> - ret = blk_co_discard(exp->blk, (request.from + exp->dev_offset)
> - / BDRV_SECTOR_SIZE,
> + /* Ignore unaligned head or tail, until block layer adds byte
> + * interface */
> + request.len -= (request.from + request.len) % BDRV_SECTOR_SIZE;
> + ret = blk_co_discard(exp->blk,
> + DIV_ROUND_UP(request.from + exp->dev_offset,
> + BDRV_SECTOR_SIZE),
> request.len / BDRV_SECTOR_SIZE);
> if (ret < 0) {
> LOG("discard failed");
>
Thanks, queued for 2.7.
Paolo
