From 4b96fa3846f001981ef6f33673cdb65f619b2997 Mon Sep 17 00:00:00 2001 From: Max Reitz Date: Tue, 5 May 2020 16:18:01 +0200 Subject: [PATCH] qcow2: Fix preallocation on block devices Calling bdrv_getlength() to get the pre-truncate file size will not really work on block devices, because they have always the same length, and trying to write beyond it will fail with a rather cryptic error message. Instead, we should use qcow2_get_last_cluster() and bdrv_getlength() only as a fallback. Before this patch: $ truncate -s 1G test.img $ sudo losetup -f --show test.img /dev/loop0 $ sudo qemu-img create -f qcow2 -o preallocation=full /dev/loop0 64M Formatting '/dev/loop0', fmt=qcow2 size=67108864 cluster_size=65536 preallocation=full lazy_refcounts=off refcount_bits=16 qemu-img: /dev/loop0: Could not resize image: Failed to resize refcount structures: No space left on device With this patch: $ sudo qemu-img create -f qcow2 -o preallocation=full /dev/loop0 64M Formatting '/dev/loop0', fmt=qcow2 size=67108864 cluster_size=65536 preallocation=full lazy_refcounts=off refcount_bits=16 qemu-img: /dev/loop0: Could not resize image: Failed to resize underlying file: Preallocation mode 'full' unsupported for this non-regular file So as you can see, it still fails, but now the problem is missing support on the block device level, so we at least get a better error message. Note that we cannot preallocate block devices on truncate by design, because we do not know what area to preallocate. Their length is always the same, the truncate operation does not change it. Signed-off-by: Max Reitz Message-Id: <20200505141801.1096763-1-mreitz@redhat.com> Signed-off-by: Kevin Wolf --- block/qcow2.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/block/qcow2.c b/block/qcow2.c index fc7d4b185ed9..11903fb54763 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -4107,7 +4107,7 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset, { int64_t allocation_start, host_offset, guest_offset; int64_t clusters_allocated; - int64_t old_file_size, new_file_size; + int64_t old_file_size, last_cluster, new_file_size; uint64_t nb_new_data_clusters, nb_new_l2_tables; /* With a data file, preallocation means just allocating the metadata @@ -4127,7 +4127,13 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset, ret = old_file_size; goto fail; } - old_file_size = ROUND_UP(old_file_size, s->cluster_size); + + last_cluster = qcow2_get_last_cluster(bs, old_file_size); + if (last_cluster >= 0) { + old_file_size = (last_cluster + 1) * s->cluster_size; + } else { + old_file_size = ROUND_UP(old_file_size, s->cluster_size); + } nb_new_data_clusters = DIV_ROUND_UP(offset - old_length, s->cluster_size);