From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40441) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YOnqb-0007GJ-Hl for qemu-devel@nongnu.org; Fri, 20 Feb 2015 08:42:30 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YOnqX-0001It-ED for qemu-devel@nongnu.org; Fri, 20 Feb 2015 08:42:25 -0500 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:40528 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YOnqW-0001Ge-U2 for qemu-devel@nongnu.org; Fri, 20 Feb 2015 08:42:21 -0500 Message-ID: <54E739B7.1010601@kamp.de> Date: Fri, 20 Feb 2015 14:42:15 +0100 From: Peter Lieven MIME-Version: 1.0 References: <7d15cff8d75566a93a52801605d8761c.squirrel@ssl.dlhnet.de> <54E4FE1B.5090202@kamp.de> <20150219120734.GB3893@noname.redhat.com> In-Reply-To: <20150219120734.GB3893@noname.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Fwd: [PATCH v2] vpc: Implement bdrv_co_get_block_status()] List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: Paolo Bonzini , "qemu-devel@nongnu.org" , "stefanha@redhat.com >> Stefan Hajnoczi" , mreitz@redhat.com Am 19.02.2015 um 13:07 schrieb Kevin Wolf: > Am 18.02.2015 um 22:03 hat Peter Lieven geschrieben: >> Am 18.02.2015 um 21:57 schrieb Peter Lieven: >>> This implements bdrv_co_get_block_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 >>> --- >>> block/vpc.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++-- >>> 1 file changed, 48 insertions(+), 2 deletions(-) >>> >>> diff --git a/block/vpc.c b/block/vpc.c >>> index 7fddbf0..1533b6a 100644 >>> --- a/block/vpc.c >>> +++ b/block/vpc.c >>> @@ -597,6 +597,51 @@ 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; >>> + int64_t start, offset, next; >>> + 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); >>> + start = offset; >>> + allocated = (offset != -1); >>> + *pnum = 0; >>> + >>> + do { >>> + /* All sectors in a block are contiguous (without using the >>> bitmap) */ >>> + n = ROUND_UP(sector_num + 1, s->block_size / BDRV_SECTOR_SIZE) >>> + - sector_num; >>> + n = MIN(n, nb_sectors); >>> + >>> + *pnum += n; >>> + sector_num += n; >>> + nb_sectors -= n; >>> + next = start + (*pnum * BDRV_SECTOR_SIZE); >>> + >>> + if (nb_sectors == 0) { >>> + break; >>> + } >>> + >>> + offset = get_sector_offset(bs, sector_num, 0); >>> + } while ((allocated && offset == next) || (!allocated && offset == -1)); >>> + >>> + if (allocated) { >>> + return BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID | start; >>> + } else { >>> + return 0; >> Shouldn't this be >> >> return BDRV_BLOCK_ZERO; >> >> ? >> >> vpc_read memsets all blocks with offset == -1 to 0x00. > Yes, but the blocks are still unallocated, as opposed to allocated as > zero clusters, and this is indicated by 0. Okay, than I somehow have to fix that up in the iscsi driver. There I tread unallocated and anchored identically. Has that changed somewhen after the initial introduction of bdrv_get_block_status? > > vpc_get_info() sets bdi->unallocated_blocks_are_zero = true, so we end > up with bdrv_co_get_block_status() returning BDRV_BLOCK_ZERO, but not > BDRV_BLOCK_ALLOCATED (which would be set if we had BDRV_BLOCK_ZERO > here). > > I'm not sure if a wrong allocated flag would cause problem currently, > but it's definitely necessary to get right once we add support for > differencing images (patches are on the list, pending review). > >> Not for this patch, but couldn't we use your new function to signifincantly speed up >> reading of continous allocated areas in vpc_read? > There aren't really contiguous blocks in VHD, you always have a bitmap > in between. In some cases it might be better to read the bitmap as well > as the two adjacent blocks and throw that buffer away in order to save > one read request, but with relatively large block sizes of VHD it's > probably not going to help that much. If there is always a bitmap between 2 clusters I do not understand the loop in your bdrv_co_get_block_status implementation for VPC? If I understand correctly you skip over the bitmaps in the loop and report continous sectors as allocated from start. If there are bitmaps in between at least qemu-img map would produce wrong output. Peter