| Message ID | 1418647857-3589-9-git-send-email-mreitz@redhat.com |
|---|---|
| State | New |
| Headers | show |
Am 15.12.2014 um 13:50 hat Max Reitz geschrieben: > qcow2_alloc_bytes() may reuse a cluster multiple times, in which case > the refcount is increased accordingly. However, if this would lead to an > overflow the function should instead just not reuse this cluster and > allocate a new one. > > Signed-off-by: Max Reitz <mreitz@redhat.com> > Reviewed-by: Eric Blake <eblake@redhat.com> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> > --- > block/qcow2-refcount.c | 31 ++++++++++++++++++++++++++++++- > 1 file changed, 30 insertions(+), 1 deletion(-) > > diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c > index db81647..fd28a13 100644 > --- a/block/qcow2-refcount.c > +++ b/block/qcow2-refcount.c > @@ -780,9 +780,11 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) > BDRVQcowState *s = bs->opaque; > int64_t offset, cluster_offset, new_cluster; > int free_in_cluster, ret; > + uint64_t refcount; > > BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_BYTES); > assert(size > 0 && size <= s->cluster_size); > + redo: > if (s->free_byte_offset == 0) { > offset = qcow2_alloc_clusters(bs, s->cluster_size); > if (offset < 0) { > @@ -790,12 +792,25 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) > } > s->free_byte_offset = offset; > } > - redo: > + > free_in_cluster = s->cluster_size - > offset_into_cluster(s, s->free_byte_offset); > if (size <= free_in_cluster) { > /* enough space in current cluster */ > offset = s->free_byte_offset; > + > + if (offset_into_cluster(s, offset) != 0) { > + /* We will have to increase the refcount of this cluster; if the > + * maximum has been reached already, this cluster cannot be used */ > + ret = qcow2_get_refcount(bs, offset >> s->cluster_bits, &refcount); > + if (ret < 0) { > + return ret; > + } else if (refcount == s->refcount_max) { > + s->free_byte_offset = 0; > + goto redo; > + } > + } > + > s->free_byte_offset += size; > free_in_cluster -= size; > if (free_in_cluster == 0) > @@ -816,6 +831,20 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) > if ((cluster_offset + s->cluster_size) == new_cluster) { > /* we are lucky: contiguous data */ > offset = s->free_byte_offset; > + > + /* Same as above: In order to reuse the cluster, the refcount has to > + * be increased; if that will not work, we are not so lucky after > + * all */ > + ret = qcow2_get_refcount(bs, offset >> s->cluster_bits, &refcount); > + if (ret < 0) { > + qcow2_free_clusters(bs, new_cluster, s->cluster_size, > + QCOW2_DISCARD_NEVER); > + return ret; > + } else if (refcount == s->refcount_max) { > + s->free_byte_offset = offset; I think you mean 0. offset is already the old value. > + goto redo; > + } > + > ret = qcow2_update_cluster_refcount(bs, offset >> s->cluster_bits, > 1, false, QCOW2_DISCARD_NEVER); > if (ret < 0) { I wonder if the code duplication is necessary. I was already thinking that there was some duplication when I reviewed the previous patch, but now it seems to become even more obvious that the three parts of this function are: 1. Allocate a new cluster 2. Allocate space in the already allocated cluster 3. Allocate a new cluster and space inside it, which is just 1. + 2. Kevin
On 2015-02-04 at 06:55, Kevin Wolf wrote: > Am 15.12.2014 um 13:50 hat Max Reitz geschrieben: >> qcow2_alloc_bytes() may reuse a cluster multiple times, in which case >> the refcount is increased accordingly. However, if this would lead to an >> overflow the function should instead just not reuse this cluster and >> allocate a new one. >> >> Signed-off-by: Max Reitz <mreitz@redhat.com> >> Reviewed-by: Eric Blake <eblake@redhat.com> >> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> >> --- >> block/qcow2-refcount.c | 31 ++++++++++++++++++++++++++++++- >> 1 file changed, 30 insertions(+), 1 deletion(-) >> >> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c >> index db81647..fd28a13 100644 >> --- a/block/qcow2-refcount.c >> +++ b/block/qcow2-refcount.c >> @@ -780,9 +780,11 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) >> BDRVQcowState *s = bs->opaque; >> int64_t offset, cluster_offset, new_cluster; >> int free_in_cluster, ret; >> + uint64_t refcount; >> >> BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_BYTES); >> assert(size > 0 && size <= s->cluster_size); >> + redo: >> if (s->free_byte_offset == 0) { >> offset = qcow2_alloc_clusters(bs, s->cluster_size); >> if (offset < 0) { >> @@ -790,12 +792,25 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) >> } >> s->free_byte_offset = offset; >> } >> - redo: >> + >> free_in_cluster = s->cluster_size - >> offset_into_cluster(s, s->free_byte_offset); >> if (size <= free_in_cluster) { >> /* enough space in current cluster */ >> offset = s->free_byte_offset; >> + >> + if (offset_into_cluster(s, offset) != 0) { >> + /* We will have to increase the refcount of this cluster; if the >> + * maximum has been reached already, this cluster cannot be used */ >> + ret = qcow2_get_refcount(bs, offset >> s->cluster_bits, &refcount); >> + if (ret < 0) { >> + return ret; >> + } else if (refcount == s->refcount_max) { >> + s->free_byte_offset = 0; >> + goto redo; >> + } >> + } >> + >> s->free_byte_offset += size; >> free_in_cluster -= size; >> if (free_in_cluster == 0) >> @@ -816,6 +831,20 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) >> if ((cluster_offset + s->cluster_size) == new_cluster) { >> /* we are lucky: contiguous data */ >> offset = s->free_byte_offset; >> + >> + /* Same as above: In order to reuse the cluster, the refcount has to >> + * be increased; if that will not work, we are not so lucky after >> + * all */ >> + ret = qcow2_get_refcount(bs, offset >> s->cluster_bits, &refcount); >> + if (ret < 0) { >> + qcow2_free_clusters(bs, new_cluster, s->cluster_size, >> + QCOW2_DISCARD_NEVER); >> + return ret; >> + } else if (refcount == s->refcount_max) { >> + s->free_byte_offset = offset; > I think you mean 0. offset is already the old value. Oh, right. Thanks for catching! >> + goto redo; >> + } >> + >> ret = qcow2_update_cluster_refcount(bs, offset >> s->cluster_bits, >> 1, false, QCOW2_DISCARD_NEVER); >> if (ret < 0) { > I wonder if the code duplication is necessary. I was already thinking > that there was some duplication when I reviewed the previous patch, but > now it seems to become even more obvious that the three parts of this > function are: > > 1. Allocate a new cluster > 2. Allocate space in the already allocated cluster > 3. Allocate a new cluster and space inside it, which is just 1. + 2. Well, I can try rewriting this function, but I guess the diffcount will be even higher. I think I'll try to write an independent patch which rewrites this function and then drop these two patches from this series. Max
Am 04.02.2015 um 16:33 hat Max Reitz geschrieben: > On 2015-02-04 at 06:55, Kevin Wolf wrote: > >Am 15.12.2014 um 13:50 hat Max Reitz geschrieben: > >>qcow2_alloc_bytes() may reuse a cluster multiple times, in which case > >>the refcount is increased accordingly. However, if this would lead to an > >>overflow the function should instead just not reuse this cluster and > >>allocate a new one. > >> > >>Signed-off-by: Max Reitz <mreitz@redhat.com> > >>Reviewed-by: Eric Blake <eblake@redhat.com> > >>Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> > >>--- > >> block/qcow2-refcount.c | 31 ++++++++++++++++++++++++++++++- > >> 1 file changed, 30 insertions(+), 1 deletion(-) > >> > >>diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c > >>index db81647..fd28a13 100644 > >>--- a/block/qcow2-refcount.c > >>+++ b/block/qcow2-refcount.c > >>@@ -780,9 +780,11 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) > >> BDRVQcowState *s = bs->opaque; > >> int64_t offset, cluster_offset, new_cluster; > >> int free_in_cluster, ret; > >>+ uint64_t refcount; > >> BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_BYTES); > >> assert(size > 0 && size <= s->cluster_size); > >>+ redo: > >> if (s->free_byte_offset == 0) { > >> offset = qcow2_alloc_clusters(bs, s->cluster_size); > >> if (offset < 0) { > >>@@ -790,12 +792,25 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) > >> } > >> s->free_byte_offset = offset; > >> } > >>- redo: > >>+ > >> free_in_cluster = s->cluster_size - > >> offset_into_cluster(s, s->free_byte_offset); > >> if (size <= free_in_cluster) { > >> /* enough space in current cluster */ > >> offset = s->free_byte_offset; > >>+ > >>+ if (offset_into_cluster(s, offset) != 0) { > >>+ /* We will have to increase the refcount of this cluster; if the > >>+ * maximum has been reached already, this cluster cannot be used */ > >>+ ret = qcow2_get_refcount(bs, offset >> s->cluster_bits, &refcount); > >>+ if (ret < 0) { > >>+ return ret; > >>+ } else if (refcount == s->refcount_max) { > >>+ s->free_byte_offset = 0; > >>+ goto redo; > >>+ } > >>+ } > >>+ > >> s->free_byte_offset += size; > >> free_in_cluster -= size; > >> if (free_in_cluster == 0) > >>@@ -816,6 +831,20 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) > >> if ((cluster_offset + s->cluster_size) == new_cluster) { > >> /* we are lucky: contiguous data */ > >> offset = s->free_byte_offset; > >>+ > >>+ /* Same as above: In order to reuse the cluster, the refcount has to > >>+ * be increased; if that will not work, we are not so lucky after > >>+ * all */ > >>+ ret = qcow2_get_refcount(bs, offset >> s->cluster_bits, &refcount); > >>+ if (ret < 0) { > >>+ qcow2_free_clusters(bs, new_cluster, s->cluster_size, > >>+ QCOW2_DISCARD_NEVER); > >>+ return ret; > >>+ } else if (refcount == s->refcount_max) { > >>+ s->free_byte_offset = offset; > >I think you mean 0. offset is already the old value. > > Oh, right. Thanks for catching! > > >>+ goto redo; > >>+ } > >>+ > >> ret = qcow2_update_cluster_refcount(bs, offset >> s->cluster_bits, > >> 1, false, QCOW2_DISCARD_NEVER); > >> if (ret < 0) { > >I wonder if the code duplication is necessary. I was already thinking > >that there was some duplication when I reviewed the previous patch, but > >now it seems to become even more obvious that the three parts of this > >function are: > > > >1. Allocate a new cluster > >2. Allocate space in the already allocated cluster > >3. Allocate a new cluster and space inside it, which is just 1. + 2. > > Well, I can try rewriting this function, but I guess the diffcount > will be even higher. > > I think I'll try to write an independent patch which rewrites this > function and then drop these two patches from this series. Anything that makes the series shorter is welcome. ;-) In fact, I've been considering merging the first few patches even if they aren't valuable in themselves, just to make v6 shorter. Kevin
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index db81647..fd28a13 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -780,9 +780,11 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) BDRVQcowState *s = bs->opaque; int64_t offset, cluster_offset, new_cluster; int free_in_cluster, ret; + uint64_t refcount; BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_BYTES); assert(size > 0 && size <= s->cluster_size); + redo: if (s->free_byte_offset == 0) { offset = qcow2_alloc_clusters(bs, s->cluster_size); if (offset < 0) { @@ -790,12 +792,25 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) } s->free_byte_offset = offset; } - redo: + free_in_cluster = s->cluster_size - offset_into_cluster(s, s->free_byte_offset); if (size <= free_in_cluster) { /* enough space in current cluster */ offset = s->free_byte_offset; + + if (offset_into_cluster(s, offset) != 0) { + /* We will have to increase the refcount of this cluster; if the + * maximum has been reached already, this cluster cannot be used */ + ret = qcow2_get_refcount(bs, offset >> s->cluster_bits, &refcount); + if (ret < 0) { + return ret; + } else if (refcount == s->refcount_max) { + s->free_byte_offset = 0; + goto redo; + } + } + s->free_byte_offset += size; free_in_cluster -= size; if (free_in_cluster == 0) @@ -816,6 +831,20 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) if ((cluster_offset + s->cluster_size) == new_cluster) { /* we are lucky: contiguous data */ offset = s->free_byte_offset; + + /* Same as above: In order to reuse the cluster, the refcount has to + * be increased; if that will not work, we are not so lucky after + * all */ + ret = qcow2_get_refcount(bs, offset >> s->cluster_bits, &refcount); + if (ret < 0) { + qcow2_free_clusters(bs, new_cluster, s->cluster_size, + QCOW2_DISCARD_NEVER); + return ret; + } else if (refcount == s->refcount_max) { + s->free_byte_offset = offset; + goto redo; + } + ret = qcow2_update_cluster_refcount(bs, offset >> s->cluster_bits, 1, false, QCOW2_DISCARD_NEVER); if (ret < 0) {