projects / mirror_qemu.git / blame
| Commit | Line | Data |
|---|---|---|
| 5135fe71 | 1 | QEMU supports the NBD protocol, and has an internal NBD client (see |
| 3229a835 VSO |
2 | block/nbd.c), an internal NBD server (see blockdev-nbd.c), and an |
| 3 | external NBD server tool (see qemu-nbd.c). The common code is placed | |
| 4 | in nbd/*. | |
| 5 | ||
| 6 | The NBD protocol is specified here: | |
| 7 | https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md | |
| 8 | ||
| 9 | The following paragraphs describe some specific properties of NBD | |
| 5135fe71 | 10 | protocol realization in QEMU. |
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11 | |
| 12 | = Metadata namespaces = | |
| 13 | ||
| 5135fe71 | 14 | QEMU supports the "base:allocation" metadata context as defined in the |
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15 | NBD protocol specification, and also defines an additional metadata |
| 16 | namespace "qemu". | |
| 17 | ||
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18 | == "qemu" namespace == |
| 19 | ||
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20 | The "qemu" namespace currently contains two available metadata context |
| 21 | types. The first is related to exposing the contents of a dirty | |
| 22 | bitmap alongside the associated disk contents. That metadata context | |
| 23 | is named with the following form: | |
| 3229a835 VSO |
24 | |
| 25 | qemu:dirty-bitmap:<dirty-bitmap-export-name> | |
| 26 | ||
| 27 | Each dirty-bitmap metadata context defines only one flag for extents | |
| 28 | in reply for NBD_CMD_BLOCK_STATUS: | |
| 29 | ||
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30 | bit 0: NBD_STATE_DIRTY, set when the extent is "dirty" |
| 31 | ||
| 32 | The second is related to exposing the source of various extents within | |
| 33 | the image, with a single metadata context named: | |
| 34 | ||
| 35 | qemu:allocation-depth | |
| 36 | ||
| 37 | In the allocation depth context, the entire 32-bit value represents a | |
| 38 | depth of which layer in a thin-provisioned backing chain provided the | |
| 39 | data (0 for unallocated, 1 for the active layer, 2 for the first | |
| 40 | backing layer, and so forth). | |
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41 | |
| 42 | For NBD_OPT_LIST_META_CONTEXT the following queries are supported | |
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43 | in addition to the specific "qemu:allocation-depth" and |
| 44 | "qemu:dirty-bitmap:<dirty-bitmap-export-name>": | |
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45 | |
| 46 | * "qemu:" - returns list of all available metadata contexts in the | |
| 47 | namespace. | |
| 48 | * "qemu:dirty-bitmap:" - returns list of all available dirty-bitmap | |
| 49 | metadata contexts. | |
| ba2d3b3a EB |
50 | |
| 51 | = Features by version = | |
| 52 | ||
| 53 | The following list documents which qemu version first implemented | |
| 54 | various features (both as a server exposing the feature, and as a | |
| 55 | client taking advantage of the feature when present), to make it | |
| 56 | easier to plan for cross-version interoperability. Note that in | |
| 57 | several cases, the initial release containing a feature may require | |
| 58 | additional patches from the corresponding stable branch to fix bugs in | |
| 59 | the operation of that feature. | |
| 60 | ||
| 61 | * 2.6: NBD_OPT_STARTTLS with TLS X.509 Certificates | |
| 62 | * 2.8: NBD_CMD_WRITE_ZEROES | |
| 63 | * 2.10: NBD_OPT_GO, NBD_INFO_BLOCK | |
| 64 | * 2.11: NBD_OPT_STRUCTURED_REPLY | |
| 65 | * 2.12: NBD_CMD_BLOCK_STATUS for "base:allocation" | |
| 66 | * 3.0: NBD_OPT_STARTTLS with TLS Pre-Shared Keys (PSK), | |
| 67 | NBD_CMD_BLOCK_STATUS for "qemu:dirty-bitmap:", NBD_CMD_CACHE | |
| 76ca4b58 | 68 | * 4.2: NBD_FLAG_CAN_MULTI_CONN for shareable read-only exports, |
| 0a479545 | 69 | NBD_CMD_FLAG_FAST_ZERO |
| 71719cd5 | 70 | * 5.2: NBD_CMD_BLOCK_STATUS for "qemu:allocation-depth" |
| 58a6fdcc | 71 | * 7.1: NBD_FLAG_CAN_MULTI_CONN for shareable writable exports |