diff options
Diffstat (limited to 'docs/interop/nbd.txt')
| -rw-r--r-- | docs/interop/nbd.txt | 23 |
1 files changed, 18 insertions, 5 deletions
diff --git a/docs/interop/nbd.txt b/docs/interop/nbd.txt index f3b3cacc96..10ce098a29 100644 --- a/docs/interop/nbd.txt +++ b/docs/interop/nbd.txt @@ -17,19 +17,31 @@ namespace "qemu". == "qemu" namespace == -The "qemu" namespace currently contains only one type of context, -related to exposing the contents of a dirty bitmap alongside the -associated disk contents. That context has the following form: +The "qemu" namespace currently contains two available metadata context +types. The first is related to exposing the contents of a dirty +bitmap alongside the associated disk contents. That metadata context +is named with the following form: qemu:dirty-bitmap:<dirty-bitmap-export-name> Each dirty-bitmap metadata context defines only one flag for extents in reply for NBD_CMD_BLOCK_STATUS: - bit 0: NBD_STATE_DIRTY, means that the extent is "dirty" + bit 0: NBD_STATE_DIRTY, set when the extent is "dirty" + +The second is related to exposing the source of various extents within +the image, with a single metadata context named: + + qemu:allocation-depth + +In the allocation depth context, the entire 32-bit value represents a +depth of which layer in a thin-provisioned backing chain provided the +data (0 for unallocated, 1 for the active layer, 2 for the first +backing layer, and so forth). For NBD_OPT_LIST_META_CONTEXT the following queries are supported -in addition to "qemu:dirty-bitmap:<dirty-bitmap-export-name>": +in addition to the specific "qemu:allocation-depth" and +"qemu:dirty-bitmap:<dirty-bitmap-export-name>": * "qemu:" - returns list of all available metadata contexts in the namespace. @@ -55,3 +67,4 @@ the operation of that feature. NBD_CMD_BLOCK_STATUS for "qemu:dirty-bitmap:", NBD_CMD_CACHE * 4.2: NBD_FLAG_CAN_MULTI_CONN for shareable read-only exports, NBD_CMD_FLAG_FAST_ZERO +* 5.2: NBD_CMD_BLOCK_STATUS for "qemu:allocation-depth" |