In CI we run make root-test via gotestsum, which executes multiple
package tests concurrently. TestAutoclearTrueLoop attempts to invoke
LOOP_CLR_FD using a device name, which introduces a race condition.
Example race:
Process P1 represents mount.test which runs TestAutoclearTrueLoop
Process P2 represents manager.test which runs TestLoopbackMount
T1: P1 closes fd of loop-device (loop3) (kernel unsets backing-file on close)
T2: P2 gets loop3 from /dev/loop-control
T3: P2 configures loop3 with backing file successfully
T4: P1 invokes removeLoop to clear backing file for loop3
You might see that failure like this
```
=== FAIL: core/mount/manager TestLoopbackMount (0.05s)
log_hook.go:47: time="2025-10-23T21:49:22.532811960Z" level=debug msg="activating mount" func="manager.(*mountManager).Activate" file="/home/runner/work/containerd/containerd/core/mount/manager/manager.go:134" mounts="[{loop /tmp/TestLoopbackMount989607109/001/fs-1621892597 []} {format/ext4 {{ mount 0 }} []}]" name=id1 testcase=TestLoopbackMount
helpers.go💯 unmount /tmp/TestLoopbackMount989607109/001/test-mount-3030342351
manager_linux_test.go:80:
Error Trace: /home/runner/work/containerd/containerd/core/mount/manager/manager_linux_test.go:80
/home/runner/work/containerd/containerd/core/mount/manager/manager_linux_test.go:105
Error: Received unexpected error:
failed to get loop device info: no such device or address
Test: TestLoopbackMount
```
To fix this, the test now compares backing-file's inode directly and does
not call removeLoop when autoclear is set.
Signed-off-by: Wei Fu <fuweid89@gmail.com>
Commit ee8ae9d569 ("Update erofs snapshotter to use mount manager")
temporarily removed the file-backed mount feature to adapt to the new
mount manager infrastructure as a quick start.
After the mount manager was introduced, a specific mount type can be
handled with a mount handler plugin to provide a dedicated mount
process (e.g. setup loopback devices in advance or calling external
mount helpers).
This commit adds a default EROFS mount handler for the Linux hosts
to set up loop devices for mount sources and "device=" external file
blobs if necessary (i.e. when file-backed mounts are unavailable),
allowing common runtimes such as runC to work directly, e.g.
``` sh
mount -t erofs /var/lib/containerd/io.containerd.snapshotter.v1.erofs/snapshots/1/layer.erofs \
/run/containerd/io.containerd.mount-manager.v1.bolt/t/346/1
```
will be handled as
``` sh
mount -t erofs /dev/loop1 /run/containerd/io.containerd.mount-manager.v1.bolt/t/346/1
```
and
``` sh
mount -t erofs /var/lib/containerd/io.containerd.snapshotter.v1.erofs/snapshots/7/fsmeta.erofs \
-odevice=/var/lib/containerd/io.containerd.snapshotter.v1.erofs/snapshots/1/layer.erofs,\
device=/var/lib/containerd/io.containerd.snapshotter.v1.erofs/snapshots/2/layer.erofs,\
...
device=/var/lib/containerd/io.containerd.snapshotter.v1.erofs/snapshots/7/layer.erofs
/run/containerd/io.containerd.mount-manager.v1.bolt/t/335/1
```
will be handled as
``` sh
mount -t erofs /dev/loop1 -odevice=/dev/loop2,device=/dev/loop3,... \
/run/containerd/io.containerd.mount-manager.v1.bolt/t/335/1
```
if file-backed mounts are unavailable.
For other host platforms (e.g. Darwin hosts) or specific runtimes
that require EROFS raw mounts instead of parsed mounts, this plugin
can be explicitly masked off by users.
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
