如何在docker中成功启用udev同步？

Question

我已docker 1.6.1从此站点下载并安装静态链接,并在以下位置运行RHEL 7.1:

[root@localhost bin]# ./docker -d
WARN[0000] Udev sync is not supported. This will lead to unexpected behavior, data loss and errors
INFO[0000] +job init_networkdriver()
INFO[0000] +job serveapi(unix:///var/run/docker.sock)
INFO[0000] Listening for HTTP on unix (/var/run/docker.sock)
INFO[0000] -job init_networkdriver() = OK (0)
INFO[0000] Loading containers: start.

INFO[0000] Loading containers: done.
INFO[0000] docker daemon: 1.6.1 97cd073; execdriver: native-0.2; graphdriver: devicemapper
INFO[0000] +job acceptconnections()
INFO[0000] -job acceptconnections() = OK (0)
INFO[0000] Daemon has completed initialization

我可以看到有一个警告:" Udev sync is not supported. This will lead to unexpected behavior, data loss and errors",在检查docker源代码后,我发现警告日志来自deviceset.go:

func (devices *DeviceSet) initDevmapper(doInit bool) error {
    ......

    // https://github.com/docker/docker/issues/4036
    if supported := devicemapper.UdevSetSyncSupport(true); !supported {
        log.Warnf("Udev sync is not supported. This will lead to unexpected behavior, data loss and errors")
    }
    log.Debugf("devicemapper: udev sync support: %v", devicemapper.UdevSyncSupported())

    ......
}

这devicemapper.UdevSetSyncSupport是这样的:

// UdevSyncSupported returns whether device-mapper is able to sync with udev
//
// This is essential otherwise race conditions can arise where both udev and
// device-mapper attempt to create and destroy devices.
func UdevSyncSupported() bool {
    return DmUdevGetSyncSupport() != 0
}

// UdevSetSyncSupport allows setting whether the udev sync should be enabled.
// The return bool indicates the state of whether the sync is enabled.
func UdevSetSyncSupport(enable bool) bool {
    if enable {
        DmUdevSetSyncSupport(1)
    } else {
        DmUdevSetSyncSupport(0)
    }
    return UdevSyncSupported()
}

我可以看到原因是启用udev同步失败.如何udev成功启用同步？

更新:检查反汇编代码后dm_udev_set_sync_support:

(gdb) disassemble dm_udev_set_sync_support
Dump of assembler code for function dm_udev_set_sync_support:
=> 0x0000000000a3e4e0 <+0>:     repz retq
End of assembler dump.

它是一个空函数,什么都不做,没有提到set sync支持.这是否意味着这个静态构建的docker二进制文件是不可用的？

Answer 1

我无法重现您的问题；我得到以下信息：

(gdb) disassemble dm_udev_set_sync_support
Dump of assembler code for function dm_udev_set_sync_support@plt:
   0x0000000000403420 <+0>:     jmpq   *0xda8c92(%rip)        # 0x11ac0b8 <dm_udev_set_sync_support@got.plt>
   0x0000000000403426 <+6>:     pushq  $0x14
   0x000000000040342b <+11>:    jmpq   0x4032d0

帮自己一个忙：忽略 docker.io 所做的构建，直接从 RHEL 获取 Docker。它可以在 Extras 频道中找到。虽然它通常会比上游版本晚几周（例如 1.6 而不是 1.7），但它也经过了良好的测试并保证实际工作。