On Tue, Jul 08, 2014 at 04:49:24PM +0200, Francesco Romani wrote: > @@ -5813,3 +5815,57 @@ void bdrv_flush_io_queue(BlockDriverState *bs) > bdrv_flush_io_queue(bs->file); > } > } > + > +static bool watermark_exceeded(BlockDriverState *bs, > + int64_t sector_num, > + int nb_sectors) > +{ > + > + if (bs->wr_watermark_perc > 0) { > + int64_t watermark = (bs->total_sectors) / 100 * > bs->wr_watermark_perc;
bs->total_sectors should not be used directly. Have you considered making the watermark parameter take sector units instead of a percentage? I'm not sure whether a precentage makes sense because 25% of a 10GB image is 2.5 GB so a 75% watermark might be reasonable. 25% of a 1 TB image is 250 GB and that's probably not a reasonable watermark. So let the block-set-watermark caller pass an absolute sector number instead. It keeps things simple for both QEMU and thin provisioning manager. > + if (sector_num >= watermark) { > + return true; > + } > + } > + return false; > +} > + > +static int coroutine_fn watermark_before_write_notify(NotifierWithReturn > *notifier, > + void *opaque) > +{ > + BdrvTrackedRequest *req = opaque; > + int64_t sector_num = req->offset >> BDRV_SECTOR_BITS; > + int nb_sectors = req->bytes >> BDRV_SECTOR_BITS; > + > +/* FIXME: needed? */ > + assert((req->offset & (BDRV_SECTOR_SIZE - 1)) == 0); > + assert((req->bytes & (BDRV_SECTOR_SIZE - 1)) == 0); Not really needed here. Emulated storage controllers either get requests in block units (i.e. they are automatically aligned) or check them (like virtio-blk). I guess there's no harm in checking, but I would drop it. > + > + if (watermark_exceeded(req->bs, sector_num, nb_sectors)) { > + BlockDriverState *bs = req->bs; > + qapi_event_send_block_watermark( > + bdrv_get_device_name(bs), > + sector_num, > + bs->wr_highest_sector, > + &error_abort); How do you prevent flooding events if every write request exceeds the watermark? Perhaps the watermark should be disabled until block-set-watermark is called again. > + } > + > + return 0; /* should always let other notifiers run */ > +} > + > +void bdrv_set_watermark_perc(BlockDriverState *bs, > + int watermark_perc) > +{ > + NotifierWithReturn before_write = { > + .notify = watermark_before_write_notify, > + }; > + > + if (watermark_perc <= 0) { > + return; > + } > + > + if (bs->wr_watermark_perc == 0) { > + bdrv_add_before_write_notifier(bs, &before_write); before_write must be a BlockDriverState field so it has the correct lifetime. In this patch before_write is allocated on the stack and will cause invalid memory accesses once we leave this function.
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