| Message ID | 20231020215622.789260-3-andrey.drobyshev@virtuozzo.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | qcow2: make subclusters discardable | expand |
On 20.10.23 23:56, Andrey Drobyshev wrote: > This helper simply obtains the l2 table parameters of the cluster which > contains the given subclusters range. Right now this info is being > obtained and used by zero_l2_subclusters(). As we're about to introduce > the subclusters discard operation, this helper would let us avoid code > duplication. > > Also introduce struct SubClusterRangeInfo, which would contain all the > needed params. > > Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com> > --- > block/qcow2-cluster.c | 90 +++++++++++++++++++++++++++++-------------- > 1 file changed, 62 insertions(+), 28 deletions(-) > > diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c > index 904f00d1b3..8801856b93 100644 > --- a/block/qcow2-cluster.c > +++ b/block/qcow2-cluster.c > @@ -32,6 +32,13 @@ > #include "qemu/memalign.h" > #include "trace.h" > > +typedef struct SubClusterRangeInfo { > + uint64_t *l2_slice; We should document that this is a strong reference that must be returned via qcow2_cache_put(). Maybe you could also define a clean-up function using G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC() that does this, allowing this type to be used with g_auto(). > + int l2_index; > + uint64_t l2_entry; > + uint64_t l2_bitmap; > +} SubClusterRangeInfo; > + > int coroutine_fn qcow2_shrink_l1_table(BlockDriverState *bs, > uint64_t exact_size) > { > @@ -1892,6 +1899,50 @@ again: > return 0; > } > > +static int get_sc_range_info(BlockDriverState *bs, uint64_t offset, > + unsigned nb_subclusters, > + SubClusterRangeInfo *scri) It would be good to have documentation for this function, for example that it only works on a single cluster, i.e. that the range denoted by @offset and @nb_subclusters must not cross a cluster boundary, and that @offset must be aligned to subclusters. In general, it is unclear to me at this point what this function does. OK, it gets the SCRI for all subclusters in the cluster at @offset (this is what its name implies), but then it also has this loop that checks whether there are compressed clusters among the @nb_subclusters. It has a comment about being unable to zero/discard subclusters in compressed clusters, but the function name says nothing about this scope of zeroing/discarding. > +{ > + BDRVQcow2State *s = bs->opaque; > + int ret, sc_cleared = 0, sc_index = offset_to_sc_index(s, offset); > + QCow2SubclusterType sctype; > + > + /* Here we only work with the subclusters within single cluster. */ > + assert(nb_subclusters > 0 && nb_subclusters < s->subclusters_per_cluster); > + assert(sc_index + nb_subclusters <= s->subclusters_per_cluster); > + assert(offset_into_subcluster(s, offset) == 0); > + > + ret = get_cluster_table(bs, offset, &scri->l2_slice, &scri->l2_index); > + if (ret < 0) { > + return ret; > + } > + > + scri->l2_entry = get_l2_entry(s, scri->l2_slice, scri->l2_index); > + scri->l2_bitmap = get_l2_bitmap(s, scri->l2_slice, scri->l2_index); > + > + do { > + qcow2_get_subcluster_range_type(bs, scri->l2_entry, scri->l2_bitmap, > + sc_index, &sctype); I think there’s a `ret = ` missing here. > + if (ret < 0) { > + return ret; > + } > + > + switch (sctype) { > + case QCOW2_SUBCLUSTER_COMPRESSED: > + /* We cannot partially zeroize/discard compressed clusters. */ > + return -ENOTSUP; > + case QCOW2_SUBCLUSTER_INVALID: > + return -EINVAL; > + default: > + break; > + } > + > + sc_cleared += ret; > + } while (sc_cleared < nb_subclusters); > + > + return 0; > +} > + > /* > * This discards as many clusters of nb_clusters as possible at once (i.e. > * all clusters in the same L2 slice) and returns the number of discarded > @@ -2097,44 +2148,27 @@ zero_l2_subclusters(BlockDriverState *bs, uint64_t offset, > unsigned nb_subclusters) > { > BDRVQcow2State *s = bs->opaque; > - uint64_t *l2_slice; > - uint64_t old_l2_bitmap, l2_bitmap; > - int l2_index, ret, sc = offset_to_sc_index(s, offset); > + uint64_t new_l2_bitmap; > + int ret, sc = offset_to_sc_index(s, offset); > + SubClusterRangeInfo scri = { 0 }; > > - /* For full clusters use zero_in_l2_slice() instead */ > - assert(nb_subclusters > 0 && nb_subclusters < s->subclusters_per_cluster); > - assert(sc + nb_subclusters <= s->subclusters_per_cluster); > - assert(offset_into_subcluster(s, offset) == 0); > - > - ret = get_cluster_table(bs, offset, &l2_slice, &l2_index); > + ret = get_sc_range_info(bs, offset, nb_subclusters, &scri); > if (ret < 0) { > - return ret; > - } > - > - switch (qcow2_get_cluster_type(bs, get_l2_entry(s, l2_slice, l2_index))) { > - case QCOW2_CLUSTER_COMPRESSED: > - ret = -ENOTSUP; /* We cannot partially zeroize compressed clusters */ > goto out; > - case QCOW2_CLUSTER_NORMAL: > - case QCOW2_CLUSTER_UNALLOCATED: > - break; > - default: > - g_assert_not_reached(); > } > > - old_l2_bitmap = l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index); > - > - l2_bitmap |= QCOW_OFLAG_SUB_ZERO_RANGE(sc, sc + nb_subclusters); > - l2_bitmap &= ~QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + nb_subclusters); > + new_l2_bitmap = scri.l2_bitmap; > + new_l2_bitmap |= QCOW_OFLAG_SUB_ZERO_RANGE(sc, sc + nb_subclusters); > + new_l2_bitmap &= ~QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + nb_subclusters); > > - if (old_l2_bitmap != l2_bitmap) { > - set_l2_bitmap(s, l2_slice, l2_index, l2_bitmap); > - qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice); > + if (new_l2_bitmap != scri.l2_bitmap) { > + set_l2_bitmap(s, scri.l2_slice, scri.l2_index, new_l2_bitmap); > + qcow2_cache_entry_mark_dirty(s->l2_table_cache, scri.l2_slice); > } > > ret = 0; > out: > - qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice); > + qcow2_cache_put(s->l2_table_cache, (void **) &scri.l2_slice); qcow2_cache_put() doesn’t look like it’s safe to be called if the table is NULL (i.e. `scri.l2_slice == NULL`). We can get here if get_sc_range_info() fails, so that may happen. I think you should either: (A) Implement G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC() for the SCRI type so it isn’t an issue (at least I assume that could solve it), or (B) Call qcow2_cache_put() here only if `scri.l2_slice != NULL`. In any case, I think it also makes sense to have get_sc_range_info() only return a valid table if it returns success, i.e. if there’s any error in get_sc_range_info(), it should clean up `scri.l2_slice` itself. Hanna > > return ret; > }
Hello Hanna, Sorry for the delay and thanks for your thorough and detailed review. On 10/31/23 17:53, Hanna Czenczek wrote: > On 20.10.23 23:56, Andrey Drobyshev wrote: >> This helper simply obtains the l2 table parameters of the cluster which >> contains the given subclusters range. Right now this info is being >> obtained and used by zero_l2_subclusters(). As we're about to introduce >> the subclusters discard operation, this helper would let us avoid code >> duplication. >> >> Also introduce struct SubClusterRangeInfo, which would contain all the >> needed params. >> >> Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com> >> --- >> block/qcow2-cluster.c | 90 +++++++++++++++++++++++++++++-------------- >> 1 file changed, 62 insertions(+), 28 deletions(-) >> >> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c >> index 904f00d1b3..8801856b93 100644 >> --- a/block/qcow2-cluster.c >> +++ b/block/qcow2-cluster.c >> @@ -32,6 +32,13 @@ >> #include "qemu/memalign.h" >> #include "trace.h" >> +typedef struct SubClusterRangeInfo { >> + uint64_t *l2_slice; > > We should document that this is a strong reference that must be returned > via qcow2_cache_put(). Maybe you could also define a clean-up function > using G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC() that does this, allowing this > type to be used with g_auto(). > >> + int l2_index; >> + uint64_t l2_entry; >> + uint64_t l2_bitmap; >> +} SubClusterRangeInfo; >> + >> int coroutine_fn qcow2_shrink_l1_table(BlockDriverState *bs, >> uint64_t exact_size) >> { >> @@ -1892,6 +1899,50 @@ again: >> return 0; >> } >> +static int get_sc_range_info(BlockDriverState *bs, uint64_t offset, >> + unsigned nb_subclusters, >> + SubClusterRangeInfo *scri) > > It would be good to have documentation for this function, for example > that it only works on a single cluster, i.e. that the range denoted by > @offset and @nb_subclusters must not cross a cluster boundary, and that > @offset must be aligned to subclusters. > I figured out those restrictions are derived from the number of asserts in the function body itself, much like it's done in zero_l2_subclusters() and friends. But of course I don't mind documenting this. > In general, it is unclear to me at this point what this function does. The sole purpose of this function is to avoid the code duplication, since both zero_l2_subclusters() (pre-existing) and discard_l2_subclusters() (newly introduced) need to obtain the same info about the subclusters range they're working with. > OK, it gets the SCRI for all subclusters in the cluster at @offset (this > is what its name implies), but then it also has this loop that checks > whether there are compressed clusters among the @nb_subclusters. Look at the pre-existing implementation of zero_l2_subclusters(): it also checks that the subcluster range we're dealing with isn't contained within a compressed cluster (otherwise there's no point zeroizing individual subclusters). So the logic isn't changed here. The only reason I decided to loop through the subclusters (instead of calling qcow2_get_cluster_type() for the whole cluster) is so that I could detect invalid subclusters and return -EINVAL right away. > It has a comment about being unable to zero/discard subclusters in compressed > clusters, but the function name says nothing about this scope of > zeroing/discarding. > Maybe rename it then to stress out that we're dealing with the regular subclusters only? get_normal_sc_range_info()? >> +{ >> + BDRVQcow2State *s = bs->opaque; >> + int ret, sc_cleared = 0, sc_index = offset_to_sc_index(s, offset); >> + QCow2SubclusterType sctype; >> + >> + /* Here we only work with the subclusters within single cluster. */ >> + assert(nb_subclusters > 0 && nb_subclusters < >> s->subclusters_per_cluster); >> + assert(sc_index + nb_subclusters <= s->subclusters_per_cluster); >> + assert(offset_into_subcluster(s, offset) == 0); >> + >> + ret = get_cluster_table(bs, offset, &scri->l2_slice, >> &scri->l2_index); >> + if (ret < 0) { >> + return ret; >> + } >> + >> + scri->l2_entry = get_l2_entry(s, scri->l2_slice, scri->l2_index); >> + scri->l2_bitmap = get_l2_bitmap(s, scri->l2_slice, scri->l2_index); >> + >> + do { >> + qcow2_get_subcluster_range_type(bs, scri->l2_entry, >> scri->l2_bitmap, >> + sc_index, &sctype); > > I think there’s a `ret = ` missing here. > Of course there is, thanks for catching this. >> + if (ret < 0) { >> + return ret; >> + } >> + >> + switch (sctype) { >> + case QCOW2_SUBCLUSTER_COMPRESSED: >> + /* We cannot partially zeroize/discard compressed >> clusters. */ >> + return -ENOTSUP; >> + case QCOW2_SUBCLUSTER_INVALID: >> + return -EINVAL; >> + default: >> + break; >> + } >> + >> + sc_cleared += ret; >> + } while (sc_cleared < nb_subclusters); >> + >> + return 0; >> +} >> + >> /* >> * This discards as many clusters of nb_clusters as possible at once >> (i.e. >> * all clusters in the same L2 slice) and returns the number of >> discarded >> @@ -2097,44 +2148,27 @@ zero_l2_subclusters(BlockDriverState *bs, >> uint64_t offset, >> unsigned nb_subclusters) >> { >> BDRVQcow2State *s = bs->opaque; >> - uint64_t *l2_slice; >> - uint64_t old_l2_bitmap, l2_bitmap; >> - int l2_index, ret, sc = offset_to_sc_index(s, offset); >> + uint64_t new_l2_bitmap; >> + int ret, sc = offset_to_sc_index(s, offset); >> + SubClusterRangeInfo scri = { 0 }; >> - /* For full clusters use zero_in_l2_slice() instead */ >> - assert(nb_subclusters > 0 && nb_subclusters < >> s->subclusters_per_cluster); >> - assert(sc + nb_subclusters <= s->subclusters_per_cluster); >> - assert(offset_into_subcluster(s, offset) == 0); >> - >> - ret = get_cluster_table(bs, offset, &l2_slice, &l2_index); >> + ret = get_sc_range_info(bs, offset, nb_subclusters, &scri); >> if (ret < 0) { >> - return ret; >> - } >> - >> - switch (qcow2_get_cluster_type(bs, get_l2_entry(s, l2_slice, >> l2_index))) { >> - case QCOW2_CLUSTER_COMPRESSED: >> - ret = -ENOTSUP; /* We cannot partially zeroize compressed >> clusters */ >> goto out; >> - case QCOW2_CLUSTER_NORMAL: >> - case QCOW2_CLUSTER_UNALLOCATED: >> - break; >> - default: >> - g_assert_not_reached(); >> } >> - old_l2_bitmap = l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index); >> - >> - l2_bitmap |= QCOW_OFLAG_SUB_ZERO_RANGE(sc, sc + nb_subclusters); >> - l2_bitmap &= ~QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + nb_subclusters); >> + new_l2_bitmap = scri.l2_bitmap; >> + new_l2_bitmap |= QCOW_OFLAG_SUB_ZERO_RANGE(sc, sc + >> nb_subclusters); >> + new_l2_bitmap &= ~QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + >> nb_subclusters); >> - if (old_l2_bitmap != l2_bitmap) { >> - set_l2_bitmap(s, l2_slice, l2_index, l2_bitmap); >> - qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice); >> + if (new_l2_bitmap != scri.l2_bitmap) { >> + set_l2_bitmap(s, scri.l2_slice, scri.l2_index, new_l2_bitmap); >> + qcow2_cache_entry_mark_dirty(s->l2_table_cache, scri.l2_slice); >> } >> ret = 0; >> out: >> - qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice); >> + qcow2_cache_put(s->l2_table_cache, (void **) &scri.l2_slice); > > qcow2_cache_put() doesn’t look like it’s safe to be called if the table > is NULL (i.e. `scri.l2_slice == NULL`). We can get here if > get_sc_range_info() fails, so that may happen. I think you should either: > > (A) Implement G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC() for the SCRI type so it > isn’t an issue (at least I assume that could solve it), or > > (B) Call qcow2_cache_put() here only if `scri.l2_slice != NULL`. > Since in patch 5 I add the code path zero_l2_subclusters() -> discard_l2_subclusters(), option (A) would only be valid if we manage to skip SCRI param on this call. If I understand correctly, you're suggesting adding a destructor for the SCRI type so that we call qcow2_cache_put() in one place and one place only when this structure goes out of the current scope. But even in this case we'd have to perform the '!= NULL' check in that destructor, the only benefit is that we do this in one place. > In any case, I think it also makes sense to have get_sc_range_info() > only return a valid table if it returns success, i.e. if there’s any > error in get_sc_range_info(), it should clean up `scri.l2_slice` itself. > Yes, this seems like a sane behaviour. > Hanna > >> return ret; >> } >
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 904f00d1b3..8801856b93 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -32,6 +32,13 @@ #include "qemu/memalign.h" #include "trace.h" +typedef struct SubClusterRangeInfo { + uint64_t *l2_slice; + int l2_index; + uint64_t l2_entry; + uint64_t l2_bitmap; +} SubClusterRangeInfo; + int coroutine_fn qcow2_shrink_l1_table(BlockDriverState *bs, uint64_t exact_size) { @@ -1892,6 +1899,50 @@ again: return 0; } +static int get_sc_range_info(BlockDriverState *bs, uint64_t offset, + unsigned nb_subclusters, + SubClusterRangeInfo *scri) +{ + BDRVQcow2State *s = bs->opaque; + int ret, sc_cleared = 0, sc_index = offset_to_sc_index(s, offset); + QCow2SubclusterType sctype; + + /* Here we only work with the subclusters within single cluster. */ + assert(nb_subclusters > 0 && nb_subclusters < s->subclusters_per_cluster); + assert(sc_index + nb_subclusters <= s->subclusters_per_cluster); + assert(offset_into_subcluster(s, offset) == 0); + + ret = get_cluster_table(bs, offset, &scri->l2_slice, &scri->l2_index); + if (ret < 0) { + return ret; + } + + scri->l2_entry = get_l2_entry(s, scri->l2_slice, scri->l2_index); + scri->l2_bitmap = get_l2_bitmap(s, scri->l2_slice, scri->l2_index); + + do { + qcow2_get_subcluster_range_type(bs, scri->l2_entry, scri->l2_bitmap, + sc_index, &sctype); + if (ret < 0) { + return ret; + } + + switch (sctype) { + case QCOW2_SUBCLUSTER_COMPRESSED: + /* We cannot partially zeroize/discard compressed clusters. */ + return -ENOTSUP; + case QCOW2_SUBCLUSTER_INVALID: + return -EINVAL; + default: + break; + } + + sc_cleared += ret; + } while (sc_cleared < nb_subclusters); + + return 0; +} + /* * This discards as many clusters of nb_clusters as possible at once (i.e. * all clusters in the same L2 slice) and returns the number of discarded @@ -2097,44 +2148,27 @@ zero_l2_subclusters(BlockDriverState *bs, uint64_t offset, unsigned nb_subclusters) { BDRVQcow2State *s = bs->opaque; - uint64_t *l2_slice; - uint64_t old_l2_bitmap, l2_bitmap; - int l2_index, ret, sc = offset_to_sc_index(s, offset); + uint64_t new_l2_bitmap; + int ret, sc = offset_to_sc_index(s, offset); + SubClusterRangeInfo scri = { 0 }; - /* For full clusters use zero_in_l2_slice() instead */ - assert(nb_subclusters > 0 && nb_subclusters < s->subclusters_per_cluster); - assert(sc + nb_subclusters <= s->subclusters_per_cluster); - assert(offset_into_subcluster(s, offset) == 0); - - ret = get_cluster_table(bs, offset, &l2_slice, &l2_index); + ret = get_sc_range_info(bs, offset, nb_subclusters, &scri); if (ret < 0) { - return ret; - } - - switch (qcow2_get_cluster_type(bs, get_l2_entry(s, l2_slice, l2_index))) { - case QCOW2_CLUSTER_COMPRESSED: - ret = -ENOTSUP; /* We cannot partially zeroize compressed clusters */ goto out; - case QCOW2_CLUSTER_NORMAL: - case QCOW2_CLUSTER_UNALLOCATED: - break; - default: - g_assert_not_reached(); } - old_l2_bitmap = l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index); - - l2_bitmap |= QCOW_OFLAG_SUB_ZERO_RANGE(sc, sc + nb_subclusters); - l2_bitmap &= ~QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + nb_subclusters); + new_l2_bitmap = scri.l2_bitmap; + new_l2_bitmap |= QCOW_OFLAG_SUB_ZERO_RANGE(sc, sc + nb_subclusters); + new_l2_bitmap &= ~QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + nb_subclusters); - if (old_l2_bitmap != l2_bitmap) { - set_l2_bitmap(s, l2_slice, l2_index, l2_bitmap); - qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice); + if (new_l2_bitmap != scri.l2_bitmap) { + set_l2_bitmap(s, scri.l2_slice, scri.l2_index, new_l2_bitmap); + qcow2_cache_entry_mark_dirty(s->l2_table_cache, scri.l2_slice); } ret = 0; out: - qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice); + qcow2_cache_put(s->l2_table_cache, (void **) &scri.l2_slice); return ret; }
This helper simply obtains the l2 table parameters of the cluster which contains the given subclusters range. Right now this info is being obtained and used by zero_l2_subclusters(). As we're about to introduce the subclusters discard operation, this helper would let us avoid code duplication. Also introduce struct SubClusterRangeInfo, which would contain all the needed params. Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com> --- block/qcow2-cluster.c | 90 +++++++++++++++++++++++++++++-------------- 1 file changed, 62 insertions(+), 28 deletions(-)