| Message ID | 961e6f3e3af13a25c666859b391b7ed147873d8b.1590429901.git.berto@igalia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add subcluster allocation to qcow2 | expand |
On 5/25/20 1:08 PM, Alberto Garcia wrote: > This patch adds QCow2SubclusterType, which is the subcluster-level > version of QCow2ClusterType. All QCOW2_SUBCLUSTER_* values have the > the same meaning as their QCOW2_CLUSTER_* equivalents (when they > exist). See below for details and caveats. > > In images without extended L2 entries clusters are treated as having > exactly one subcluster so it is possible to replace one data type with > the other while keeping the exact same semantics. > > With extended L2 entries there are new possible values, and every > subcluster in the same cluster can obviously have a different > QCow2SubclusterType so functions need to be adapted to work on the > subcluster level. > > There are several things that have to be taken into account: > > a) QCOW2_SUBCLUSTER_COMPRESSED means that the whole cluster is > compressed. We do not support compression at the subcluster > level. > > b) There are two different values for unallocated subclusters: > QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN which means that the whole > cluster is unallocated, and QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC > which means that the cluster is allocated but the subcluster is > not. The latter can only happen in images with extended L2 > entries. > > c) QCOW2_SUBCLUSTER_INVALID is used to detect the cases where an L2 > entry has a value that violates the specification. The caller is > responsible for handling these situations. > > To prevent compatibility problems with images that have invalid > values but are currently being read by QEMU without causing side > effects, QCOW2_SUBCLUSTER_INVALID is only returned for images > with extended L2 entries. > > qcow2_cluster_to_subcluster_type() is added as a separate function > from qcow2_get_subcluster_type(), but this is only temporary and both > will be merged in a subsequent patch. > > Signed-off-by: Alberto Garcia <berto@igalia.com> > --- > block/qcow2.h | 126 +++++++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 125 insertions(+), 1 deletion(-) > > diff --git a/block/qcow2.h b/block/qcow2.h > index 5c6bf48c7a..27dbcbc502 100644 > --- a/block/qcow2.h > +++ b/block/qcow2.h > @@ -80,6 +80,21 @@ > > #define QCOW_EXTL2_SUBCLUSTERS_PER_CLUSTER 32 > > +/* The subcluster X [0..31] is allocated */ > +#define QCOW_OFLAG_SUB_ALLOC(X) (1ULL << (X)) > +/* The subcluster X [0..31] reads as zeroes */ > +#define QCOW_OFLAG_SUB_ZERO(X) (QCOW_OFLAG_SUB_ALLOC(X) << 32) > +/* Subclusters [X, Y) (0 <= X <= Y <= 32) are allocated */ As you are now using a half-open range, should this be: (0 <= X < Y <= 32) > +#define QCOW_OFLAG_SUB_ALLOC_RANGE(X, Y) \ > + (QCOW_OFLAG_SUB_ALLOC(Y) - QCOW_OFLAG_SUB_ALLOC(X)) with <= instead of <, then it is impossible to distinguish between QCOW_OFLAG_SUB_ALLOC_RANGE(0,0) and QCOW_OFLAG_SUB_ALLOC_RANGE(31,31) which both resolve to 0. I guess it depends on whether the later uses of this macro require a non-zero mask ('X < Y') or tolerate the corner case of no subclusters selected ('X <= Y'). > +/* Subclusters [X, Y) (0 <= X <= Y <= 32) read as zeroes */ > +#define QCOW_OFLAG_SUB_ZERO_RANGE(X, Y) \ > + (QCOW_OFLAG_SUB_ALLOC_RANGE(X, Y) << 32) > +/* L2 entry bitmap with all allocation bits set */ > +#define QCOW_L2_BITMAP_ALL_ALLOC (QCOW_OFLAG_SUB_ALLOC_RANGE(0, 32)) > +/* L2 entry bitmap with all "read as zeroes" bits set */ > +#define QCOW_L2_BITMAP_ALL_ZEROES (QCOW_OFLAG_SUB_ZERO_RANGE(0, 32)) > + Fixing the comment (if necessary) does not change the code, and the rest of this patch is fine, so: Reviewed-by: Eric Blake <eblake@redhat.com>
On Tue 26 May 2020 10:32:08 PM CEST, Eric Blake wrote: >> +/* The subcluster X [0..31] is allocated */ >> +#define QCOW_OFLAG_SUB_ALLOC(X) (1ULL << (X)) >> +/* The subcluster X [0..31] reads as zeroes */ >> +#define QCOW_OFLAG_SUB_ZERO(X) (QCOW_OFLAG_SUB_ALLOC(X) << 32) >> +/* Subclusters [X, Y) (0 <= X <= Y <= 32) are allocated */ > > As you are now using a half-open range, should this be: > (0 <= X < Y <= 32) I changed the macros because I wanted to allow cases where X == Y. The reason is the new qcow2_get_subcluster_range_type() function: case QCOW2_SUBCLUSTER_NORMAL: val = l2_bitmap | QCOW_OFLAG_SUB_ALLOC_RANGE(0, sc_from); return cto32(val) - sc_from; If sc_from is 0 then the result of the macro is also 0, and 'val' equals the lower 32 bits (allocation status bits) of the L2 bitmap, as expected. >> +#define QCOW_OFLAG_SUB_ALLOC_RANGE(X, Y) \ >> + (QCOW_OFLAG_SUB_ALLOC(Y) - QCOW_OFLAG_SUB_ALLOC(X)) > > with <= instead of <, then it is impossible to distinguish between > QCOW_OFLAG_SUB_ALLOC_RANGE(0,0) and QCOW_OFLAG_SUB_ALLOC_RANGE(31,31) > which both resolve to 0. Exactly, there is no difference and there should not be. Berto
On 5/27/20 4:51 AM, Alberto Garcia wrote: > On Tue 26 May 2020 10:32:08 PM CEST, Eric Blake wrote: >>> +/* The subcluster X [0..31] is allocated */ >>> +#define QCOW_OFLAG_SUB_ALLOC(X) (1ULL << (X)) >>> +/* The subcluster X [0..31] reads as zeroes */ >>> +#define QCOW_OFLAG_SUB_ZERO(X) (QCOW_OFLAG_SUB_ALLOC(X) << 32) >>> +/* Subclusters [X, Y) (0 <= X <= Y <= 32) are allocated */ >> >> As you are now using a half-open range, should this be: >> (0 <= X < Y <= 32) > > I changed the macros because I wanted to allow cases where X == Y. > > The reason is the new qcow2_get_subcluster_range_type() function: > > case QCOW2_SUBCLUSTER_NORMAL: > val = l2_bitmap | QCOW_OFLAG_SUB_ALLOC_RANGE(0, sc_from); > return cto32(val) - sc_from; > > If sc_from is 0 then the result of the macro is also 0, and 'val' equals > the lower 32 bits (allocation status bits) of the L2 bitmap, as > expected. > >>> +#define QCOW_OFLAG_SUB_ALLOC_RANGE(X, Y) \ >>> + (QCOW_OFLAG_SUB_ALLOC(Y) - QCOW_OFLAG_SUB_ALLOC(X)) >> >> with <= instead of <, then it is impossible to distinguish between >> QCOW_OFLAG_SUB_ALLOC_RANGE(0,0) and QCOW_OFLAG_SUB_ALLOC_RANGE(31,31) >> which both resolve to 0. > > Exactly, there is no difference and there should not be. Okay, then with that explanation, I agree that the comment is correct as written.
diff --git a/block/qcow2.h b/block/qcow2.h index 5c6bf48c7a..27dbcbc502 100644 --- a/block/qcow2.h +++ b/block/qcow2.h @@ -80,6 +80,21 @@ #define QCOW_EXTL2_SUBCLUSTERS_PER_CLUSTER 32 +/* The subcluster X [0..31] is allocated */ +#define QCOW_OFLAG_SUB_ALLOC(X) (1ULL << (X)) +/* The subcluster X [0..31] reads as zeroes */ +#define QCOW_OFLAG_SUB_ZERO(X) (QCOW_OFLAG_SUB_ALLOC(X) << 32) +/* Subclusters [X, Y) (0 <= X <= Y <= 32) are allocated */ +#define QCOW_OFLAG_SUB_ALLOC_RANGE(X, Y) \ + (QCOW_OFLAG_SUB_ALLOC(Y) - QCOW_OFLAG_SUB_ALLOC(X)) +/* Subclusters [X, Y) (0 <= X <= Y <= 32) read as zeroes */ +#define QCOW_OFLAG_SUB_ZERO_RANGE(X, Y) \ + (QCOW_OFLAG_SUB_ALLOC_RANGE(X, Y) << 32) +/* L2 entry bitmap with all allocation bits set */ +#define QCOW_L2_BITMAP_ALL_ALLOC (QCOW_OFLAG_SUB_ALLOC_RANGE(0, 32)) +/* L2 entry bitmap with all "read as zeroes" bits set */ +#define QCOW_L2_BITMAP_ALL_ZEROES (QCOW_OFLAG_SUB_ZERO_RANGE(0, 32)) + /* Size of normal and extended L2 entries */ #define L2E_SIZE_NORMAL (sizeof(uint64_t)) #define L2E_SIZE_EXTENDED (sizeof(uint64_t) * 2) @@ -462,6 +477,33 @@ typedef struct QCowL2Meta QLIST_ENTRY(QCowL2Meta) next_in_flight; } QCowL2Meta; +/* + * In images with standard L2 entries all clusters are treated as if + * they had one subcluster so QCow2ClusterType and QCow2SubclusterType + * can be mapped to each other and have the exact same meaning + * (QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC cannot happen in these images). + * + * In images with extended L2 entries QCow2ClusterType refers to the + * complete cluster and QCow2SubclusterType to each of the individual + * subclusters, so there are several possible combinations: + * + * |--------------+---------------------------| + * | Cluster type | Possible subcluster types | + * |--------------+---------------------------| + * | UNALLOCATED | UNALLOCATED_PLAIN | + * | | ZERO_PLAIN | + * |--------------+---------------------------| + * | NORMAL | UNALLOCATED_ALLOC | + * | | ZERO_ALLOC | + * | | NORMAL | + * |--------------+---------------------------| + * | COMPRESSED | COMPRESSED | + * |--------------+---------------------------| + * + * QCOW2_SUBCLUSTER_INVALID means that the L2 entry is incorrect and + * the image should be marked corrupt. + */ + typedef enum QCow2ClusterType { QCOW2_CLUSTER_UNALLOCATED, QCOW2_CLUSTER_ZERO_PLAIN, @@ -470,6 +512,16 @@ typedef enum QCow2ClusterType { QCOW2_CLUSTER_COMPRESSED, } QCow2ClusterType; +typedef enum QCow2SubclusterType { + QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN, + QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC, + QCOW2_SUBCLUSTER_ZERO_PLAIN, + QCOW2_SUBCLUSTER_ZERO_ALLOC, + QCOW2_SUBCLUSTER_NORMAL, + QCOW2_SUBCLUSTER_COMPRESSED, + QCOW2_SUBCLUSTER_INVALID, +} QCow2SubclusterType; + typedef enum QCow2MetadataOverlap { QCOW2_OL_MAIN_HEADER_BITNR = 0, QCOW2_OL_ACTIVE_L1_BITNR = 1, @@ -634,9 +686,11 @@ static inline int64_t qcow2_vm_state_offset(BDRVQcow2State *s) static inline QCow2ClusterType qcow2_get_cluster_type(BlockDriverState *bs, uint64_t l2_entry) { + BDRVQcow2State *s = bs->opaque; + if (l2_entry & QCOW_OFLAG_COMPRESSED) { return QCOW2_CLUSTER_COMPRESSED; - } else if (l2_entry & QCOW_OFLAG_ZERO) { + } else if ((l2_entry & QCOW_OFLAG_ZERO) && !has_subclusters(s)) { if (l2_entry & L2E_OFFSET_MASK) { return QCOW2_CLUSTER_ZERO_ALLOC; } @@ -656,6 +710,76 @@ static inline QCow2ClusterType qcow2_get_cluster_type(BlockDriverState *bs, } } +/* + * For an image without extended L2 entries, return the + * QCow2SubclusterType equivalent of a given QCow2ClusterType. + */ +static inline +QCow2SubclusterType qcow2_cluster_to_subcluster_type(QCow2ClusterType type) +{ + switch (type) { + case QCOW2_CLUSTER_COMPRESSED: + return QCOW2_SUBCLUSTER_COMPRESSED; + case QCOW2_CLUSTER_ZERO_PLAIN: + return QCOW2_SUBCLUSTER_ZERO_PLAIN; + case QCOW2_CLUSTER_ZERO_ALLOC: + return QCOW2_SUBCLUSTER_ZERO_ALLOC; + case QCOW2_CLUSTER_NORMAL: + return QCOW2_SUBCLUSTER_NORMAL; + case QCOW2_CLUSTER_UNALLOCATED: + return QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN; + default: + g_assert_not_reached(); + } +} + +/* + * In an image without subsclusters @l2_bitmap is ignored and + * @sc_index must be 0. + * Return QCOW2_SUBCLUSTER_INVALID if an invalid l2 entry is detected + * (this checks the whole entry and bitmap, not only the bits related + * to subcluster @sc_index). + */ +static inline +QCow2SubclusterType qcow2_get_subcluster_type(BlockDriverState *bs, + uint64_t l2_entry, + uint64_t l2_bitmap, + unsigned sc_index) +{ + BDRVQcow2State *s = bs->opaque; + QCow2ClusterType type = qcow2_get_cluster_type(bs, l2_entry); + assert(sc_index < s->subclusters_per_cluster); + + if (has_subclusters(s)) { + switch (type) { + case QCOW2_CLUSTER_COMPRESSED: + return QCOW2_SUBCLUSTER_COMPRESSED; + case QCOW2_CLUSTER_NORMAL: + if ((l2_bitmap >> 32) & l2_bitmap) { + return QCOW2_SUBCLUSTER_INVALID; + } else if (l2_bitmap & QCOW_OFLAG_SUB_ZERO(sc_index)) { + return QCOW2_SUBCLUSTER_ZERO_ALLOC; + } else if (l2_bitmap & QCOW_OFLAG_SUB_ALLOC(sc_index)) { + return QCOW2_SUBCLUSTER_NORMAL; + } else { + return QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC; + } + case QCOW2_CLUSTER_UNALLOCATED: + if (l2_bitmap & QCOW_L2_BITMAP_ALL_ALLOC) { + return QCOW2_SUBCLUSTER_INVALID; + } else if (l2_bitmap & QCOW_OFLAG_SUB_ZERO(sc_index)) { + return QCOW2_SUBCLUSTER_ZERO_PLAIN; + } else { + return QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN; + } + default: + g_assert_not_reached(); + } + } else { + return qcow2_cluster_to_subcluster_type(type); + } +} + /* Check whether refcounts are eager or lazy */ static inline bool qcow2_need_accurate_refcounts(BDRVQcow2State *s) {
This patch adds QCow2SubclusterType, which is the subcluster-level version of QCow2ClusterType. All QCOW2_SUBCLUSTER_* values have the the same meaning as their QCOW2_CLUSTER_* equivalents (when they exist). See below for details and caveats. In images without extended L2 entries clusters are treated as having exactly one subcluster so it is possible to replace one data type with the other while keeping the exact same semantics. With extended L2 entries there are new possible values, and every subcluster in the same cluster can obviously have a different QCow2SubclusterType so functions need to be adapted to work on the subcluster level. There are several things that have to be taken into account: a) QCOW2_SUBCLUSTER_COMPRESSED means that the whole cluster is compressed. We do not support compression at the subcluster level. b) There are two different values for unallocated subclusters: QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN which means that the whole cluster is unallocated, and QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC which means that the cluster is allocated but the subcluster is not. The latter can only happen in images with extended L2 entries. c) QCOW2_SUBCLUSTER_INVALID is used to detect the cases where an L2 entry has a value that violates the specification. The caller is responsible for handling these situations. To prevent compatibility problems with images that have invalid values but are currently being read by QEMU without causing side effects, QCOW2_SUBCLUSTER_INVALID is only returned for images with extended L2 entries. qcow2_cluster_to_subcluster_type() is added as a separate function from qcow2_get_subcluster_type(), but this is only temporary and both will be merged in a subsequent patch. Signed-off-by: Alberto Garcia <berto@igalia.com> --- block/qcow2.h | 126 +++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 125 insertions(+), 1 deletion(-)