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Bug 1337409 - Mounting volume read-write under read-only volume mount fails
Summary: Mounting volume read-write under read-only volume mount fails
Keywords:
Status: CLOSED NOTABUG
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: docker
Version: 7.2
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Daniel Walsh
QA Contact: atomic-bugs@redhat.com
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2016-05-19 07:06 UTC by Jan Pazdziora
Modified: 2019-03-06 01:08 UTC (History)
2 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2016-06-03 18:29:12 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)

Description Jan Pazdziora 2016-05-19 07:06:20 UTC 
Description of problem:

When software wants to generate output in its subdirectory, it might be useful to mount volume for the output read-write, while reading the software itself read-only. Attempt to do that fails.

Version-Release number of selected component (if applicable):

docker-1.9.1-40.el7.x86_64

How reproducible:

Deterministic.

Steps to Reproduce:
1. mkdir -p /tmp/parent-ro /tmp/child-rw
2. docker run -ti -v /tmp/parent-ro:/data:ro -v /tmp/child-rw:/data/_build:Z rhel7 bash

Actual results:

Timestamp: 2016-05-19 03:02:32.120707018 -0400 EDT
Code: System error

Message: mkdir /var/lib/docker/devicemapper/mnt/7279426326d7425f6f2c4c501c9ae43ce25a490a2b1bc11f392a9205fa11992c/rootfs/data/_build: read-only file system

Frames:
---
0: setupRootfs
Package: github.com/opencontainers/runc/libcontainer
File: rootfs_linux.go@40
---
1: Init
Package: github.com/opencontainers/runc/libcontainer.(*linuxStandardInit)
File: standard_init_linux.go@57
---
2: StartInitialization
Package: github.com/opencontainers/runc/libcontainer.(*LinuxFactory)
File: factory_linux.go@242
---
3: initializer
Package: github.com/docker/docker/daemon/execdriver/native
File: init.go@35
---
4: Init
Package: github.com/docker/docker/pkg/reexec
File: reexec.go@26
---
5: main
Package: main
File: docker.go@18
---
6: main
Package: runtime
File: proc.go@63
---
7: goexit
Package: runtime
File: asm_amd64.s@2232
Error response from daemon: Cannot start container 7279426326d7425f6f2c4c501c9ae43ce25a490a2b1bc11f392a9205fa11992c: [8] System error: mkdir /var/lib/docker/devicemapper/mnt/7279426326d7425f6f2c4c501c9ae43ce25a490a2b1bc11f392a9205fa11992c/rootfs/data/_build: read-only file system

Expected results:

Container started, both volumes mounted.

Additional info:
Comment 2 Daniel Walsh 2016-06-03 18:29:12 UTC 
1. mkdir -p /tmp/parent-ro /tmp/child-rw
2. docker run -ti -v /tmp/parent-ro:/data:ro -v /tmp/child-rw:/data/_build:Z rhel7 bash

The problem here is docker attempts to create the _build directory under /tmp/parent-ro after it is mounted ro.

1. mkdir -p /tmp/parent-ro/_build /tmp/child-rw


Would fix the problem.

There is no way to fix this since you started with a readonly directory.
Comment 3 Jan Pazdziora 2016-06-07 16:08:04 UTC 
You are right, this fixes the problem. Thank you.
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