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authorEric Blake <eblake@redhat.com>2017-05-06 19:05:52 -0500
committerMax Reitz <mreitz@redhat.com>2017-05-11 14:28:07 +0200
commitd2cb36af2b0040d421b347e6e4e803e07220f78d (patch)
treef44bece1bc4c24dde4d33057ad6f499e89047cc3 /block/qcow2-snapshot.c
parentf10ee139adee1c18d399dc57a7ee22a03fa59513 (diff)
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qcow2: Discard/zero clusters by byte count
Passing a byte offset, but sector count, when we ultimately want to operate on cluster granularity, is madness. Clean up the external interfaces to take both offset and count as bytes, while still keeping the assertion added previously that the caller must align the values to a cluster. Then rename things to make sure backports don't get confused by changed units: instead of qcow2_discard_clusters() and qcow2_zero_clusters(), we now have qcow2_cluster_discard() and qcow2_cluster_zeroize(). The internal functions still operate on clusters at a time, and return an int for number of cleared clusters; but on an image with 2M clusters, a single L2 table holds 256k entries that each represent a 2M cluster, totalling well over INT_MAX bytes if we ever had a request for that many bytes at once. All our callers currently limit themselves to 32-bit bytes (and therefore fewer clusters), but by making this function 64-bit clean, we have one less place to clean up if we later improve the block layer to support 64-bit bytes through all operations (with the block layer auto-fragmenting on behalf of more-limited drivers), rather than the current state where some interfaces are artificially limited to INT_MAX at a time. Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-id: 20170507000552.20847-13-eblake@redhat.com Signed-off-by: Max Reitz <mreitz@redhat.com>
Diffstat (limited to 'block/qcow2-snapshot.c')
-rw-r--r--block/qcow2-snapshot.c7
1 files changed, 3 insertions, 4 deletions
diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 0324243..44243e0 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -440,10 +440,9 @@ int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
/* The VM state isn't needed any more in the active L1 table; in fact, it
* hurts by causing expensive COW for the next snapshot. */
- qcow2_discard_clusters(bs, qcow2_vm_state_offset(s),
- align_offset(sn->vm_state_size, s->cluster_size)
- >> BDRV_SECTOR_BITS,
- QCOW2_DISCARD_NEVER, false);
+ qcow2_cluster_discard(bs, qcow2_vm_state_offset(s),
+ align_offset(sn->vm_state_size, s->cluster_size),
+ QCOW2_DISCARD_NEVER, false);
#ifdef DEBUG_ALLOC
{