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nbd: Add 'qemu-nbd -A' to expose allocation depth

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Allow the server to expose an additional metacontext to be requested
by savvy clients.  qemu-nbd adds a new option -A to expose the
qemu:allocation-depth metacontext through NBD_CMD_BLOCK_STATUS; this
can also be set via QMP when using block-export-add.

qemu as client is hacked into viewing the key aspects of this new
context by abusing the already-experimental x-dirty-bitmap option to
collapse all depths greater than 2, which results in a tri-state value
visible in the output of 'qemu-img map --output=json' (yes, that means
x-dirty-bitmap is now a bit of a misnomer, but I didn't feel like
renaming it as it would introduce a needless break of back-compat,
even though we make no compat guarantees with x- members):

unallocated (depth 0) => "zero":false, "data":true
local (depth 1)       => "zero":false, "data":false
backing (depth 2+)    => "zero":true,  "data":true

libnbd as client is probably a nicer way to get at the information
without having to decipher such hacks in qemu as client. ;)

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20201027050556.269064-11-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
This commit is contained in:
Eric Blake
2020-10-27 00:05:55 -05:00
parent 71719cd57f
commit dbc7b01492
9 changed files with 151 additions and 11 deletions
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12
qemu-nbd.c
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@@ -100,6 +100,7 @@ static void usage(const char *name)
"\n"
"Exposing part of the image:\n"
" -o, --offset=OFFSET offset into the image\n"
" -A, --allocation-depth expose the allocation depth\n"
" -B, --bitmap=NAME expose a persistent dirty bitmap\n"
"\n"
"General purpose options:\n"
@@ -524,7 +525,7 @@ int main(int argc, char **argv)
char *device = NULL;
QemuOpts *sn_opts = NULL;
const char *sn_id_or_name = NULL;
const char *sopt = "hVb:o:p:rsnc:dvk:e:f:tl:x:T:D:B:L";
const char *sopt = "hVb:o:p:rsnc:dvk:e:f:tl:x:T:D:AB:L";
struct option lopt[] = {
{ "help", no_argument, NULL, 'h' },
{ "version", no_argument, NULL, 'V' },
@@ -533,6 +534,7 @@ int main(int argc, char **argv)
{ "socket", required_argument, NULL, 'k' },
{ "offset", required_argument, NULL, 'o' },
{ "read-only", no_argument, NULL, 'r' },
{ "allocation-depth", no_argument, NULL, 'A' },
{ "bitmap", required_argument, NULL, 'B' },
{ "connect", required_argument, NULL, 'c' },
{ "disconnect", no_argument, NULL, 'd' },
@@ -575,6 +577,7 @@ int main(int argc, char **argv)
const char *export_name = NULL; /* defaults to "" later for server mode */
const char *export_description = NULL;
strList *bitmaps = NULL;
bool alloc_depth = false;
const char *tlscredsid = NULL;
bool imageOpts = false;
bool writethrough = true;
@@ -689,6 +692,9 @@ int main(int argc, char **argv)
readonly = true;
flags &= ~BDRV_O_RDWR;
break;
case 'A':
alloc_depth = true;
break;
case 'B':
QAPI_LIST_PREPEND(bitmaps, g_strdup(optarg));
break;
@@ -787,7 +793,7 @@ int main(int argc, char **argv)
}
if (export_name || export_description || dev_offset ||
device || disconnect || fmt || sn_id_or_name || bitmaps ||
seen_aio || seen_discard || seen_cache) {
alloc_depth || seen_aio || seen_discard || seen_cache) {
error_report("List mode is incompatible with per-device settings");
exit(EXIT_FAILURE);
}
@@ -1073,6 +1079,8 @@ int main(int argc, char **argv)
.description = g_strdup(export_description),
.has_bitmaps = !!bitmaps,
.bitmaps = bitmaps,
.has_allocation_depth = alloc_depth,
.allocation_depth = alloc_depth,
},
};
blk_exp_add(export_opts, &error_fatal);