Am 11.02.2015 um 23:51 hat Max Reitz geschrieben: > On 2015-02-11 at 11:23, Kevin Wolf wrote: > >This implements bdrv_co_get_status() for VHD images. This can > >significantly speed up qemu-img convert operation because only with this > >function implemented sparseness can be considered. (Before, converting a > >1 TB empty image took several minutes for me, now it's instantaneous.) > > > >Signed-off-by: Kevin Wolf <kw...@redhat.com> > >--- > > block/vpc.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++-- > > 1 file changed, 52 insertions(+), 2 deletions(-) > > > >diff --git a/block/vpc.c b/block/vpc.c > >index 46803b1..379ff4a 100644 > >--- a/block/vpc.c > >+++ b/block/vpc.c > >@@ -597,6 +597,55 @@ static coroutine_fn int vpc_co_write(BlockDriverState > >*bs, int64_t sector_num, > > return ret; > > } > >+static int64_t coroutine_fn vpc_co_get_block_status(BlockDriverState *bs, > >+ int64_t sector_num, int nb_sectors, int *pnum) > >+{ > >+ BDRVVPCState *s = bs->opaque; > >+ VHDFooter *footer = (VHDFooter *) s->footer_buf; > > Double space before the left parenthesis.
Fun. As it happens, I copied this line from elsewhere... > >+ int64_t start, offset; > >+ bool allocated; > >+ int n; > >+ > >+ if (be32_to_cpu(footer->type) == VHD_FIXED) { > >+ *pnum = nb_sectors; > >+ return BDRV_BLOCK_RAW | BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_DATA | > >+ (sector_num << BDRV_SECTOR_BITS); > >+ } > >+ > >+ offset = get_sector_offset(bs, sector_num, 0); > >+ > >+ *pnum = 1; > >+ start = offset; > >+ allocated = (offset != -1); > >+ nb_sectors--; > >+ > >+ while (nb_sectors > 0) { > >+ offset = get_sector_offset(bs, sector_num, 0); > > During the first iteration, this will is exactly the function call > as the one before this loop. > > >+ > >+ if ((offset != -1) != allocated) { > >+ break; > >+ } > >+ > >+ if (allocated && offset != start + (*pnum * 512)) { > > Therefore, if allocated is true, this check will always fail because > offset == start. Whoops, thanks for catching that. I'll fix it, even though it doesn't seem to have any practicel consequences. VHD is a format braindead enough that you never get two contiguous blocks anyway. There's always a bitmap in between. > >+ break; > >+ } > >+ > >+ /* All sectors in a block are contiguous (without using the bitmap) > >*/ > >+ n = ROUND_UP(sector_num + 1, s->block_size / 512) - sector_num; > >+ n = MIN(n, nb_sectors); > > I think you can make use of this assumption even before calling > get_sector_offset() in the first iteration. Hm... Maybe I need to make it a do-while loop to get rid of some duplication with the first iteration. > Also, 512 is shorter than BDRV_SECTOR_SIZE and it's nice to get it > on a single line, but I think not introducing another literal 512 in > the code would be nicer; the same applies above in "*pnum * 512". Fair enough. Kevin