On Tue, Jul 21, 2020 at 07:51:00AM +0800, Qu Wenruo wrote: > > > On 2020/7/21 上午12:09, David Sterba wrote: > > On Mon, Jul 20, 2020 at 08:51:08PM +0800, Qu Wenruo wrote: > >> --- a/convert/source-ext2.c > >> +++ b/convert/source-ext2.c > >> @@ -87,7 +87,8 @@ static int ext2_open_fs(struct btrfs_convert_context *cctx, const char *name) > >> cctx->fs_data = ext2_fs; > >> cctx->blocksize = ext2_fs->blocksize; > >> cctx->block_count = ext2_fs->super->s_blocks_count; > >> - cctx->total_bytes = ext2_fs->blocksize * ext2_fs->super->s_blocks_count; > >> + cctx->total_bytes = (u64)ext2_fs->blocksize * > >> + (u64)ext2_fs->super->s_blocks_count; > > > > Do you need to cast both? Once one of the types is wide enough for the > > result, there should be no loss. > > > I just want to be extra safe. Typecasts in code raise questions why are they needed, 'to be extra' safe is not a good reason. One typecast in multiplication/shifts is a common pattern to widen the result but two look more like lack of understanding of the integer promotion rules.
