2 * QEMU Enhanced Disk Format
4 * Copyright IBM, Corp. 2010
7 * Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
8 * Anthony Liguori <aliguori@us.ibm.com>
10 * This work is licensed under the terms of the GNU LGPL, version 2 or later.
11 * See the COPYING.LIB file in the top-level directory.
18 #include "block_int.h"
20 /* The layout of a QED file is as follows:
22 * +--------+----------+----------+----------+-----+
23 * | header | L1 table | cluster0 | cluster1 | ... |
24 * +--------+----------+----------+----------+-----+
26 * There is a 2-level pagetable for cluster allocation:
32 * +----------+ | +----------+
33 * | L2 table | ... | L2 table |
34 * +----------+ +----------+
36 * +----------+ | +----------+
37 * | Data | ... | Data |
38 * +----------+ +----------+
40 * The L1 table is fixed size and always present. L2 tables are allocated on
41 * demand. The L1 table size determines the maximum possible image size; it
42 * can be influenced using the cluster_size and table_size values.
44 * All fields are little-endian on disk.
48 QED_MAGIC
= 'Q' | 'E' << 8 | 'D' << 16 | '\0' << 24,
50 /* The image supports a backing file */
51 QED_F_BACKING_FILE
= 0x01,
53 /* The backing file format must not be probed, treat as raw image */
54 QED_F_BACKING_FORMAT_NO_PROBE
= 0x04,
56 /* Feature bits must be used when the on-disk format changes */
57 QED_FEATURE_MASK
= QED_F_BACKING_FILE
| /* supported feature bits */
58 QED_F_BACKING_FORMAT_NO_PROBE
,
59 QED_COMPAT_FEATURE_MASK
= 0, /* supported compat feature bits */
60 QED_AUTOCLEAR_FEATURE_MASK
= 0, /* supported autoclear feature bits */
62 /* Data is stored in groups of sectors called clusters. Cluster size must
63 * be large to avoid keeping too much metadata. I/O requests that have
64 * sub-cluster size will require read-modify-write.
66 QED_MIN_CLUSTER_SIZE
= 4 * 1024, /* in bytes */
67 QED_MAX_CLUSTER_SIZE
= 64 * 1024 * 1024,
68 QED_DEFAULT_CLUSTER_SIZE
= 64 * 1024,
70 /* Allocated clusters are tracked using a 2-level pagetable. Table size is
71 * a multiple of clusters so large maximum image sizes can be supported
72 * without jacking up the cluster size too much.
74 QED_MIN_TABLE_SIZE
= 1, /* in clusters */
75 QED_MAX_TABLE_SIZE
= 16,
76 QED_DEFAULT_TABLE_SIZE
= 4,
80 uint32_t magic
; /* QED\0 */
82 uint32_t cluster_size
; /* in bytes */
83 uint32_t table_size
; /* for L1 and L2 tables, in clusters */
84 uint32_t header_size
; /* in clusters */
86 uint64_t features
; /* format feature bits */
87 uint64_t compat_features
; /* compatible feature bits */
88 uint64_t autoclear_features
; /* self-resetting feature bits */
90 uint64_t l1_table_offset
; /* in bytes */
91 uint64_t image_size
; /* total logical image size, in bytes */
93 /* if (features & QED_F_BACKING_FILE) */
94 uint32_t backing_filename_offset
; /* in bytes from start of header */
95 uint32_t backing_filename_size
; /* in bytes */
99 BlockDriverState
*bs
; /* device */
100 uint64_t file_size
; /* length of image file, in bytes */
102 QEDHeader header
; /* always cpu-endian */
103 uint32_t table_nelems
;
110 * Round down to the start of a cluster
112 static inline uint64_t qed_start_of_cluster(BDRVQEDState
*s
, uint64_t offset
)
114 return offset
& ~(uint64_t)(s
->header
.cluster_size
- 1);
118 * Test if a cluster offset is valid
120 static inline bool qed_check_cluster_offset(BDRVQEDState
*s
, uint64_t offset
)
122 uint64_t header_size
= (uint64_t)s
->header
.header_size
*
123 s
->header
.cluster_size
;
125 if (offset
& (s
->header
.cluster_size
- 1)) {
128 return offset
>= header_size
&& offset
< s
->file_size
;
132 * Test if a table offset is valid
134 static inline bool qed_check_table_offset(BDRVQEDState
*s
, uint64_t offset
)
136 uint64_t end_offset
= offset
+ (s
->header
.table_size
- 1) *
137 s
->header
.cluster_size
;
140 if (end_offset
<= offset
) {
144 return qed_check_cluster_offset(s
, offset
) &&
145 qed_check_cluster_offset(s
, end_offset
);
148 #endif /* BLOCK_QED_H */