fix(convert): wait for nbd device release before qemu-img convert

[imlk0]

Problem

test-convert intermittently fails at step 11 with:

qemu-img: Could not open '.../input.qcow2.work': Failed to get shared "write" lock
Is another process using the image [ .../input.qcow2.work ]?
make: *** [Makefile:215: run-convert-test-case] Error 1

Example failing run: https://github.com/openanolis/cryptpilot/actions/runs/36511833625/job/109231935489

Root cause

At step 11 (cryptpilot-convert.sh), the nbd device was detached with a fixed guard:

qemu-nbd --disconnect "${device}"
sleep 2 # wait for the qemu-nbd daemon to release the file lock
...
qemu-img convert -p -O qcow2 "${work_file}" "${output_file}"

qemu-nbd --disconnect returns before the nbd daemon finishes exiting and releases the OFD write lock it holds on the backing image. The fixed sleep 2 covers it most of the time but is a race: under CI load the lock can still be held when qemu-img convert opens the image, so it bails out.

A first attempt polled blockdev --getsize64 (== 0 means free device). That is not a reliable signal — confirmed on this PR's own CI, the device reports size 0 within the same millisecond as --disconnect while the daemon still holds the file lock, so the poll exits immediately and the race is back.

Fix

Replace the fixed sleep with disk::nbd_disconnect_and_wait, which disconnects and then polls lsof on the image file (lsof -t "${image}"): once no process holds the file open, the daemon has exited and the OFD write lock is released. qemu-img convert only runs after the lock is truly gone. The loop is bounded by interval + max attempts (never blocks forever); on timeout it warns and proceeds rather than hard-failing.

lsof is already installed by the test harness (tool_packages=(qemu-img cryptsetup veritysetup lvm2 parted e2fsprogs lsof ...)).

Assisted-by

Assisted-by: Claude:claude-opus-4-8

[ostest-bot]

@imlk0 ，您好，您的请求已接收，请耐心等待结果。

[ostest-bot]

@imlk0 ，您好，未检测到有镜像需要构建，如需重新检测请评论 /start 。

[ostest-bot]

@imlk0 ，您好，您的请求已接收，请耐心等待结果。

[ostest-bot]

@imlk0 ，您好，未检测到有镜像需要构建，如需重新检测请评论 /start 。