Re: [libvirt PATCH 2/2] storage_file: add support to probe cluster_size from QCOW2 images
On Thu, May 13, 2021 at 13:23:05 +0200, Pavel Hrdina wrote:
>From QEMU docs/interop/qcow2.txt :
Byte 20 - 23: cluster_bits
Number of bits that are used for addressing an offset
within a cluster (1 << cluster_bits is the cluster size).
With this patch libvirt will be able to report the current cluster_size
for all existing storage volumes managed by storage driver.
Signed-off-by: Pavel Hrdina <phrdina(a)redhat.com>
---
src/storage/storage_util.c | 3 ++
src/storage_file/storage_file_probe.c | 55 +++++++++++++++++++--------
2 files changed, 42 insertions(+), 16 deletions(-)
[...]
diff --git a/src/storage_file/storage_file_probe.c
b/src/storage_file/storage_file_probe.c
index afe64da02e..423597049f 100644
--- a/src/storage_file/storage_file_probe.c
+++ b/src/storage_file/storage_file_probe.c
@@ -94,6 +94,9 @@ struct FileTypeInfo {
/* Store a COW base image path (possibly relative),
* or NULL if there is no COW base image, to RES;
* return BACKING_STORE_* */
+ int clusterBitsOffset; /* Byte offset from start of file where we find
+ * number of cluster bits, -1 to skip. */
+ int clusterBitsSize; /* Number of bytes for cluster bits. */
This isn't actually used [1].
const struct FileEncryptionInfo *cryptInfo; /* Encryption info
*/
int (*getBackingStore)(char **res, int *format,
const char *buf, size_t buf_size);
Given how the value is stored in the header it seems that it won't
really be usable for any other format. I think we should parse it via a
callback rather than the generic offset/size parser.
Specifically since the cluster size is stored as number of bits.
@@ -116,7 +119,8 @@ qedGetBackingStore(char **, int *, const char *,
size_t);
#define QCOWX_HDR_VERSION (4)
#define QCOWX_HDR_BACKING_FILE_OFFSET (QCOWX_HDR_VERSION+4)
#define QCOWX_HDR_BACKING_FILE_SIZE (QCOWX_HDR_BACKING_FILE_OFFSET+8)
-#define QCOWX_HDR_IMAGE_SIZE (QCOWX_HDR_BACKING_FILE_SIZE+4+4)
+#define QCOWX_HDR_CLUSTER_BITS_OFFSET (QCOWX_HDR_BACKING_FILE_SIZE+4)
+#define QCOWX_HDR_IMAGE_SIZE (QCOWX_HDR_CLUSTER_BITS_OFFSET+4)
#define QCOW1_HDR_CRYPT (QCOWX_HDR_IMAGE_SIZE+8+1+1+2)
#define QCOW2_HDR_CRYPT (QCOWX_HDR_IMAGE_SIZE+8)
G_STATIC_ASSERT(G_N_ELEMENTS(fileTypeInfo) ==
VIR_STORAGE_FILE_LAST);
@@ -890,6 +896,23 @@ virStorageFileProbeGetMetadata(virStorageSource *meta,
meta->capacity *= fileTypeInfo[meta->format].sizeMultiplier;
}
+ if (fileTypeInfo[meta->format].clusterBitsOffset != -1) {
+ int clusterBits = 0;
+
+ if ((fileTypeInfo[meta->format].clusterBitsOffset + 4) > len)
[1] ... you hardcode the value.
+ return 0;
+
+ if (fileTypeInfo[meta->format].endian == LV_LITTLE_ENDIAN)
+ clusterBits = virReadBufInt32LE(buf +
+
fileTypeInfo[meta->format].clusterBitsOffset);
+ else
+ clusterBits = virReadBufInt32BE(buf +
+
fileTypeInfo[meta->format].clusterBitsOffset);
+
+ if (clusterBits > 0)
+ meta->clusterSize = 1 << clusterBits;
+ }
+
VIR_FREE(meta->backingStoreRaw);
if (fileTypeInfo[meta->format].getBackingStore != NULL) {
int store =
fileTypeInfo[meta->format].getBackingStore(&meta->backingStoreRaw,
--
2.31.1