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From: | Max Reitz |
Subject: | Re: [Qemu-devel] [PATCH v5 07/26] qcow2: Respect error in qcow2_alloc_bytes() |
Date: | Wed, 04 Feb 2015 10:04:37 -0500 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 |
On 2015-02-04 at 06:40, Kevin Wolf wrote:
Am 15.12.2014 um 13:50 hat Max Reitz geschrieben:qcow2_update_cluster_refcount() may fail, and qcow2_alloc_bytes() should mind that case. Signed-off-by: Max Reitz <address@hidden> Reviewed-by: Eric Blake <address@hidden> Reviewed-by: Stefan Hajnoczi <address@hidden> --- block/qcow2-refcount.c | 33 +++++++++++++++++++++------------ 1 file changed, 21 insertions(+), 12 deletions(-) diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index 0308a7e..db81647 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -778,8 +778,8 @@ int qcow2_alloc_clusters_at(BlockDriverState *bs, uint64_t offset, int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) { BDRVQcowState *s = bs->opaque; - int64_t offset, cluster_offset; - int free_in_cluster; + int64_t offset, cluster_offset, new_cluster; + int free_in_cluster, ret;BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_BYTES);assert(size > 0 && size <= s->cluster_size); @@ -800,23 +800,32 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) free_in_cluster -= size; if (free_in_cluster == 0) s->free_byte_offset = 0; - if (offset_into_cluster(s, offset) != 0) - qcow2_update_cluster_refcount(bs, offset >> s->cluster_bits, 1, - false, QCOW2_DISCARD_NEVER); + if (offset_into_cluster(s, offset) != 0) { + ret = qcow2_update_cluster_refcount(bs, offset >> s->cluster_bits, + 1, false, QCOW2_DISCARD_NEVER); + if (ret < 0) { + return ret;Not sure how relevant it is, but s->free_byte_offset has already been increased, so we're leaving sub-cluster space unused. (It's not really leaking as freeing all references still frees the cluster.)
Right, will fix.
+ } + } } else { - offset = qcow2_alloc_clusters(bs, s->cluster_size); - if (offset < 0) { - return offset; + new_cluster = qcow2_alloc_clusters(bs, s->cluster_size); + if (new_cluster < 0) { + return new_cluster; }offset is the return value of this function, and now there are cases where it isn't set to new_cluster any more (I wonder why gcc doesn't warn).
Because @offset is always set. In case the next condition is true, it is set to s->free_byte_offset, just like it was before. In case it isn't, s->free_byte_offset will be set to @new_cluster and the loop will be started again (probably always resulting in size <= free_in_cluster being true and thus @offset being set to s->free_byte_offset).
Why can't we keep offset where it was used and only assign new_cluster additionally so we can do the cleanup?
Why should we? If I were a reader of this code, I think it would confuse me to have two variables holding the same value but for some reason only using @offset, but once it's been overwritten, suddenly using @new_cluster (whereas one could just use @new_cluster everywhere, and then writing @offset would be superfluous). Also, the idea was having @offset hold the offset of where the compressed data is to be stored, whereas @new_cluster is just the offset of a new cluster, but not necessarily the offset where compressed data will be stored (it won't be if (cluster_offset + s->cluster_size) == new_cluster).
Max
cluster_offset = start_of_cluster(s, s->free_byte_offset); - if ((cluster_offset + s->cluster_size) == offset) { + if ((cluster_offset + s->cluster_size) == new_cluster) { /* we are lucky: contiguous data */ offset = s->free_byte_offset; - qcow2_update_cluster_refcount(bs, offset >> s->cluster_bits, 1, - false, QCOW2_DISCARD_NEVER); + ret = qcow2_update_cluster_refcount(bs, offset >> s->cluster_bits, + 1, false, QCOW2_DISCARD_NEVER); + if (ret < 0) { + qcow2_free_clusters(bs, new_cluster, s->cluster_size, + QCOW2_DISCARD_NEVER); + return ret; + } s->free_byte_offset += size; } else { - s->free_byte_offset = offset; + s->free_byte_offset = new_cluster; goto redo; } }Kevin
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