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nbd/server: Optimize final chunk of sparse read 

If we are careful to handle 0-length read requests correctly,
we can optimize our sparse read to send the NBD_REPLY_FLAG_DONE
bit on our last OFFSET_DATA or OFFSET_HOLE chunk rather than
needing a separate chunk.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20171107030912.23930-3-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
This commit is contained in:
Eric Blake 2017-11-06 21:09:12 -06:00
parent 418638d3e4
commit e2de3256c3
1 changed files with 7 additions and 6 deletions
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13
nbd/server.c
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@ -1339,12 +1339,14 @@ static int coroutine_fn nbd_co_send_sparse_read(NBDClient *client,
offset + progress,
size - progress, &pnum, NULL,
NULL);
bool final;
if (status < 0) {
error_setg_errno(errp, -status, "unable to check for holes");
return status;
}
assert(pnum && pnum <= size - progress);
final = progress + pnum == size;
if (status & BDRV_BLOCK_ZERO) {
NBDStructuredReadHole chunk;
struct iovec iov[] = {
@ -1353,7 +1355,8 @@ static int coroutine_fn nbd_co_send_sparse_read(NBDClient *client,
trace_nbd_co_send_structured_read_hole(handle, offset + progress,
pnum);
set_be_chunk(&chunk.h, 0, NBD_REPLY_TYPE_OFFSET_HOLE,
set_be_chunk(&chunk.h, final ? NBD_REPLY_FLAG_DONE : 0,
NBD_REPLY_TYPE_OFFSET_HOLE,
handle, sizeof(chunk) - sizeof(chunk.h));
stq_be_p(&chunk.offset, offset + progress);
stl_be_p(&chunk.length, pnum);
@ -1366,7 +1369,7 @@ static int coroutine_fn nbd_co_send_sparse_read(NBDClient *client,
break;
}
ret = nbd_co_send_structured_read(client, handle, offset + progress,
data + progress, pnum, false,
data + progress, pnum, final,
errp);
}
@ -1375,9 +1378,6 @@ static int coroutine_fn nbd_co_send_sparse_read(NBDClient *client,
}
progress += pnum;
}
if (!ret) {
ret = nbd_co_send_structured_done(client, handle, errp);
}
return ret;
}
@ -1542,7 +1542,8 @@ static coroutine_fn void nbd_trip(void *opaque)
}
}
if (client->structured_reply && !(request.flags & NBD_CMD_FLAG_DF)) {
if (client->structured_reply && !(request.flags & NBD_CMD_FLAG_DF) &&
request.len) {
ret = nbd_co_send_sparse_read(req->client, request.handle,
request.from, req->data, request.len,
&local_err);