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qcow2: Don't assume 0 is an invalid cluster offset

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The cluster allocation code uses 0 as an invalid offset that is used in
case of errors or as "offset not yet determined". With external data
files, a host cluster offset of 0 becomes valid, though.

Define a constant INV_OFFSET (which is not cluster aligned and will
therefore never be a valid offset) that can be used for such purposes.

This removes the additional host_offset == 0 check that commit
ff52aab2df introduced; the confusion between an invalid offset and
(erroneous) allocation at offset 0 is removed with this change.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2019-01-18 14:40:36 +01:00
parent b8c8353a38
commit c6d619cc12
2 changed files with 29 additions and 32 deletions
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59
block/qcow2-cluster.c
View File

@ -1109,9 +1109,9 @@ static int handle_dependencies(BlockDriverState *bs, uint64_t guest_offset,
/*
* Checks how many already allocated clusters that don't require a copy on
* write there are at the given guest_offset (up to *bytes). If
* *host_offset is not zero, only physically contiguous clusters beginning at
* this host offset are counted.
* write there are at the given guest_offset (up to *bytes). If *host_offset is
* not INV_OFFSET, only physically contiguous clusters beginning at this host
* offset are counted.
*
* Note that guest_offset may not be cluster aligned. In this case, the
* returned *host_offset points to exact byte referenced by guest_offset and
@ -1143,8 +1143,8 @@ static int handle_copied(BlockDriverState *bs, uint64_t guest_offset,
trace_qcow2_handle_copied(qemu_coroutine_self(), guest_offset, *host_offset,
*bytes);
assert(*host_offset == 0 || offset_into_cluster(s, guest_offset)
== offset_into_cluster(s, *host_offset));
assert(*host_offset == INV_OFFSET || offset_into_cluster(s, guest_offset)
== offset_into_cluster(s, *host_offset));
/*
* Calculate the number of clusters to look for. We stop at L2 slice
@ -1182,7 +1182,7 @@ static int handle_copied(BlockDriverState *bs, uint64_t guest_offset,
goto out;
}
if (*host_offset != 0 && !offset_matches) {
if (*host_offset != INV_OFFSET && !offset_matches) {
*bytes = 0;
ret = 0;
goto out;
@ -1225,10 +1225,10 @@ out:
* contain the number of clusters that have been allocated and are contiguous
* in the image file.
*
* If *host_offset is non-zero, it specifies the offset in the image file at
* which the new clusters must start. *nb_clusters can be 0 on return in this
* case if the cluster at host_offset is already in use. If *host_offset is
* zero, the clusters can be allocated anywhere in the image file.
* If *host_offset is not INV_OFFSET, it specifies the offset in the image file
* at which the new clusters must start. *nb_clusters can be 0 on return in
* this case if the cluster at host_offset is already in use. If *host_offset
* is INV_OFFSET, the clusters can be allocated anywhere in the image file.
*
* *host_offset is updated to contain the offset into the image file at which
* the first allocated cluster starts.
@ -1247,7 +1247,7 @@ static int do_alloc_cluster_offset(BlockDriverState *bs, uint64_t guest_offset,
/* Allocate new clusters */
trace_qcow2_cluster_alloc_phys(qemu_coroutine_self());
if (*host_offset == 0) {
if (*host_offset == INV_OFFSET) {
int64_t cluster_offset =
qcow2_alloc_clusters(bs, *nb_clusters * s->cluster_size);
if (cluster_offset < 0) {
@ -1267,8 +1267,8 @@ static int do_alloc_cluster_offset(BlockDriverState *bs, uint64_t guest_offset,
/*
* Allocates new clusters for an area that either is yet unallocated or needs a
* copy on write. If *host_offset is non-zero, clusters are only allocated if
* the new allocation can match the specified host offset.
* copy on write. If *host_offset is not INV_OFFSET, clusters are only
* allocated if the new allocation can match the specified host offset.
*
* Note that guest_offset may not be cluster aligned. In this case, the
* returned *host_offset points to exact byte referenced by guest_offset and
@ -1296,7 +1296,7 @@ static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset,
int ret;
bool keep_old_clusters = false;
uint64_t alloc_cluster_offset = 0;
uint64_t alloc_cluster_offset = INV_OFFSET;
trace_qcow2_handle_alloc(qemu_coroutine_self(), guest_offset, *host_offset,
*bytes);
@ -1335,7 +1335,7 @@ static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset,
if (qcow2_get_cluster_type(bs, entry) == QCOW2_CLUSTER_ZERO_ALLOC &&
(entry & QCOW_OFLAG_COPIED) &&
(!*host_offset ||
(*host_offset == INV_OFFSET ||
start_of_cluster(s, *host_offset) == (entry & L2E_OFFSET_MASK)))
{
int preallocated_nb_clusters;
@ -1367,9 +1367,10 @@ static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset,
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
if (!alloc_cluster_offset) {
if (alloc_cluster_offset == INV_OFFSET) {
/* Allocate, if necessary at a given offset in the image file */
alloc_cluster_offset = start_of_cluster(s, *host_offset);
alloc_cluster_offset = *host_offset == INV_OFFSET ? INV_OFFSET :
start_of_cluster(s, *host_offset);
ret = do_alloc_cluster_offset(bs, guest_offset, &alloc_cluster_offset,
&nb_clusters);
if (ret < 0) {
@ -1382,16 +1383,7 @@ static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset,
return 0;
}
/* !*host_offset would overwrite the image header and is reserved for
* "no host offset preferred". If 0 was a valid host offset, it'd
* trigger the following overlap check; do that now to avoid having an
* invalid value in *host_offset. */
if (!alloc_cluster_offset) {
ret = qcow2_pre_write_overlap_check(bs, 0, alloc_cluster_offset,
nb_clusters * s->cluster_size);
assert(ret < 0);
goto fail;
}
assert(alloc_cluster_offset != INV_OFFSET);
}
/*
@ -1483,14 +1475,14 @@ int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
again:
start = offset;
remaining = *bytes;
cluster_offset = 0;
*host_offset = 0;
cluster_offset = INV_OFFSET;
*host_offset = INV_OFFSET;
cur_bytes = 0;
*m = NULL;
while (true) {
if (!*host_offset) {
if (*host_offset == INV_OFFSET && cluster_offset != INV_OFFSET) {
*host_offset = start_of_cluster(s, cluster_offset);
}
@ -1498,7 +1490,10 @@ again:
start += cur_bytes;
remaining -= cur_bytes;
cluster_offset += cur_bytes;
if (cluster_offset != INV_OFFSET) {
cluster_offset += cur_bytes;
}
if (remaining == 0) {
break;
@ -1570,7 +1565,7 @@ again:
*bytes -= remaining;
assert(*bytes > 0);
assert(*host_offset != 0);
assert(*host_offset != INV_OFFSET);
return 0;
}

2
block/qcow2.h
View File

@ -463,6 +463,8 @@ typedef enum QCow2MetadataOverlap {
#define REFT_OFFSET_MASK 0xfffffffffffffe00ULL
#define INV_OFFSET (-1ULL)
static inline bool has_data_file(BlockDriverState *bs)
{
BDRVQcow2State *s = bs->opaque;