From c018040299805135af45098641391a2818ddac8a Mon Sep 17 00:00:00 2001 From: Maxim Levitsky Date: Mon, 26 Aug 2019 09:19:44 +0200 Subject: [PATCH 4/4] qemu-img: Enable BDRV_REQ_MAY_UNMAP in convert RH-Author: Maxim Levitsky Message-id: <20190826091944.16113-2-mlevitsk@redhat.com> Patchwork-id: 90164 O-Subject: [RHEL-7.7.z qemu-kvm-rhev PATCH v3 1/1] qemu-img: Enable BDRV_REQ_MAY_UNMAP in convert Bugzilla: 1648622 RH-Acked-by: John Snow RH-Acked-by: Max Reitz RH-Acked-by: Stefano Garzarella From: Nir Soffer With Kevin's "block: Fix slow pre-zeroing in qemu-img convert"[1] (commit c9fdcf202f, 'qemu-img: Use BDRV_REQ_NO_FALLBACK for pre-zeroing') we skip the pre zero step called like this: blk_make_zero(s->target, BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) And we write zeroes later using: blk_co_pwrite_zeroes(s->target, sector_num << BDRV_SECTOR_BITS, n << BDRV_SECTOR_BITS, 0); Since we use flags=0, this is translated to NBD_CMD_WRITE_ZEROES with NBD_CMD_FLAG_NO_HOLE flag, which cause the NBD server to allocated space instead of punching a hole. Here is an example failure: $ dd if=/dev/urandom of=src.img bs=1M count=5 $ truncate -s 50m src.img $ truncate -s 50m dst.img $ nbdkit -f -v -e '' -U nbd.sock file file=dst.img $ ./qemu-img convert -n src.img nbd:unix:nbd.sock We can see in nbdkit log that it received the NBD_CMD_FLAG_NO_HOLE (may_trim=0): nbdkit: file[1]: debug: newstyle negotiation: flags: export 0x4d nbdkit: file[1]: debug: pwrite count=2097152 offset=0 nbdkit: file[1]: debug: pwrite count=2097152 offset=2097152 nbdkit: file[1]: debug: pwrite count=1048576 offset=4194304 nbdkit: file[1]: debug: zero count=33554432 offset=5242880 may_trim=0 nbdkit: file[1]: debug: zero count=13631488 offset=38797312 may_trim=0 nbdkit: file[1]: debug: flush And the image became fully allocated: $ qemu-img info dst.img virtual size: 50M (52428800 bytes) disk size: 50M With this change we see that nbdkit did not receive the NBD_CMD_FLAG_NO_HOLE (may_trim=1): nbdkit: file[1]: debug: newstyle negotiation: flags: export 0x4d nbdkit: file[1]: debug: pwrite count=2097152 offset=0 nbdkit: file[1]: debug: pwrite count=2097152 offset=2097152 nbdkit: file[1]: debug: pwrite count=1048576 offset=4194304 nbdkit: file[1]: debug: zero count=33554432 offset=5242880 may_trim=1 nbdkit: file[1]: debug: zero count=13631488 offset=38797312 may_trim=1 nbdkit: file[1]: debug: flush And the file is sparse as expected: $ qemu-img info dst.img virtual size: 50M (52428800 bytes) disk size: 5.0M [1] http://lists.nongnu.org/archive/html/qemu-block/2019-03/msg00761.html Signed-off-by: Nir Soffer Signed-off-by: Kevin Wolf (cherry picked from commit a3d6ae2299eaab1bced05551d0a0abfbcd9d08d0) Signed-off-by: Maxim Levitsky Signed-off-by: Miroslav Rezanina --- qemu-img.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/qemu-img.c b/qemu-img.c index d588183..f7c1483 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -1738,7 +1738,8 @@ static int coroutine_fn convert_co_write(ImgConvertState *s, int64_t sector_num, } ret = blk_co_pwrite_zeroes(s->target, sector_num << BDRV_SECTOR_BITS, - n << BDRV_SECTOR_BITS, 0); + n << BDRV_SECTOR_BITS, + BDRV_REQ_MAY_UNMAP); if (ret < 0) { return ret; } -- 1.8.3.1