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[PATCH v5 11/12] nbd: Expose actual depth in qemu:allocation-depth
From: |
Eric Blake |
Subject: |
[PATCH v5 11/12] nbd: Expose actual depth in qemu:allocation-depth |
Date: |
Fri, 23 Oct 2020 13:36:51 -0500 |
Preserve the tri-state encoding in the low bits, as that still remains
a valuable way to utilize qemu-img map with x-dirty-bitmap for
accessing quick information without needing a third-party NBD client.
But now that the block layer gives us an actual depth, we can easily
expose it in the remaining bits of our metadata context (leaving two
bits reserved, to make it easier to read depth out of a raw hex
number). This assumes no one runs a backing chain larger than 256M
elements.
iotest 309 remains unchanged (an example of the above-mentioned
x-dirty-bitmap hack); actually testing the new bits requires libnbd or
a similar client, and I didn't want to make iotests depend on libnbd
at this point in time; rather, see the libnbd project for interop
tests that exercise this new feature.
Signed-off-by: Eric Blake <eblake@redhat.com>
---
docs/interop/nbd.txt | 6 +++++-
include/block/nbd.h | 2 ++
nbd/server.c | 27 +++++++++++++++------------
3 files changed, 22 insertions(+), 13 deletions(-)
diff --git a/docs/interop/nbd.txt b/docs/interop/nbd.txt
index 7e948bd42218..d90723ffe991 100644
--- a/docs/interop/nbd.txt
+++ b/docs/interop/nbd.txt
@@ -34,7 +34,8 @@ the image, with a single metadata context named:
qemu:allocation-depth
-In the allocation depth context, bits 0 and 1 form a tri-state value:
+In the allocation depth context, bits 0 and 1 form a tri-state value,
+along with 28 bits giving an actual depth:
bits 0-1: 00: NBD_STATE_DEPTH_UNALLOC, the extent is unallocated
01: NBD_STATE_DEPTH_LOCAL, the extent is allocated in the
@@ -42,6 +43,9 @@ In the allocation depth context, bits 0 and 1 form a
tri-state value:
10: NBD_STATE_DEPTH_BACKING, the extent is inherited from a
backing layer
11: invalid, never returned
+ bits 2-3: reserved, always 0
+ bits 4-31: NBD_STATE_DEPTH_RAW, the backing layer depth (0 if
+ UNALLOC, 1 for LOCAL, 2 or more for BACKING)
For NBD_OPT_LIST_META_CONTEXT the following queries are supported
in addition to the specific "qemu:allocation-depth" and
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 956687f5c368..3c0692aec642 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -264,6 +264,8 @@ enum {
#define NBD_STATE_DEPTH_UNALLOC 0x0
#define NBD_STATE_DEPTH_LOCAL 0x1
#define NBD_STATE_DEPTH_BACKING 0x2
+#define NBD_STATE_DEPTH_RAW_MASK 0xfffffff0
+#define NBD_STATE_DEPTH_RAW_SHIFT 4
static inline bool nbd_reply_type_is_error(int type)
{
diff --git a/nbd/server.c b/nbd/server.c
index 53526090b0a2..afa79e63a7a6 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -2037,22 +2037,25 @@ static int blockalloc_to_extents(BlockDriverState *bs,
uint64_t offset,
while (bytes) {
uint32_t flags;
int64_t num;
- int ret = bdrv_is_allocated(bs, offset, bytes, &num);
+ int depth = bdrv_is_allocated_above(bs, NULL, false, offset, bytes,
+ &num);
- if (ret < 0) {
- return ret;
- }
-
- if (ret == 1) {
+ switch (depth) {
+ case 0:
+ flags = NBD_STATE_DEPTH_UNALLOC;
+ break;
+ case 1:
flags = NBD_STATE_DEPTH_LOCAL;
- } else {
- ret = bdrv_is_allocated_above(bs, NULL, false, offset, num,
- &num);
- if (ret < 0) {
- return ret;
+ break;
+ default:
+ if (depth < 0) {
+ return depth;
}
- flags = ret ? NBD_STATE_DEPTH_BACKING : NBD_STATE_DEPTH_UNALLOC;
+ flags = NBD_STATE_DEPTH_BACKING;
+ break;
}
+ assert(depth <= UINT32_MAX >> NBD_STATE_DEPTH_RAW_SHIFT);
+ flags |= depth << NBD_STATE_DEPTH_RAW_SHIFT;
if (nbd_extent_array_add(ea, num, flags) < 0) {
return 0;
--
2.29.0
- [PATCH v5 05/12] nbd: Add 'qemu-nbd -A' to expose allocation depth, (continued)
- [PATCH v5 05/12] nbd: Add 'qemu-nbd -A' to expose allocation depth, Eric Blake, 2020/10/23
- [PATCH v5 06/12] nbd: Update qapi to support exporting multiple bitmaps, Eric Blake, 2020/10/23
- [PATCH v5 08/12] nbd: Refactor counting of metadata contexts, Eric Blake, 2020/10/23
- [PATCH v5 07/12] nbd: Simplify qemu bitmap context name, Eric Blake, 2020/10/23
- [PATCH v5 09/12] nbd: Allow export of multiple bitmaps for one device, Eric Blake, 2020/10/23
- [PATCH v5 10/12] block: Return depth level during bdrv_is_allocated_above, Eric Blake, 2020/10/23
- [PATCH v5 11/12] nbd: Expose actual depth in qemu:allocation-depth,
Eric Blake <=
- [PATCH v5 12/12] qapi: Use QAPI_LIST_ADD() where possible, Eric Blake, 2020/10/23
- Re: [PATCH v5 00/12] Exposing backing-chain allocation over NBD, Eric Blake, 2020/10/23