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− | = The problem = | + | = Problem = |
| A mount namespace is a tree of mount points. In addition, mounts have another type of dependencies which is called groups. Each mount can be a member of two groups, it can be a slave in one group and a member of another group. Currently groups can’t be set, it can be only inherited from a source mount. It is always a problem when more than one type of properties have to restored for one call. This means that we have to find a sequence of steps to get a required state. | | A mount namespace is a tree of mount points. In addition, mounts have another type of dependencies which is called groups. Each mount can be a member of two groups, it can be a slave in one group and a member of another group. Currently groups can’t be set, it can be only inherited from a source mount. It is always a problem when more than one type of properties have to restored for one call. This means that we have to find a sequence of steps to get a required state. |
| In case of mount namespaces, one more problem is over-mounts. A few mounts may be over-mounted or processes can have file descriptors which are linked with over-mounted files. | | In case of mount namespaces, one more problem is over-mounts. A few mounts may be over-mounted or processes can have file descriptors which are linked with over-mounted files. |
| Another difficulty is that we are not able to create bind-mounts between namespaces, but each file system have to be mounted from a specified user namespace. | | Another difficulty is that we are not able to create bind-mounts between namespaces, but each file system have to be mounted from a specified user namespace. |
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− | = The solution = | + | = Solution = |
| When we see all variation of commands to build a mount tree, we can understand that the final picture may be very complicated to be repeated, so we suggest to add [https://patchwork.kernel.org/patch/9703885/ a new flag] to the mount() syscall, which allows us to add a mount into an existing group. | | When we see all variation of commands to build a mount tree, we can understand that the final picture may be very complicated to be repeated, so we suggest to add [https://patchwork.kernel.org/patch/9703885/ a new flag] to the mount() syscall, which allows us to add a mount into an existing group. |
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| = Source code = | | = Source code = |
− | [https://github.com/avagin/criu/tree/mntns-2.0 github.com/avagin/criu/tree/mntns-2.0] | + | * [https://github.com/avagin/criu/tree/mntns-2.0 github.com/avagin/criu/tree/mntns-2.0] |
| + | * [https://lkml.org/lkml/2017/5/9/634 [PATCH] fs: add an ioctl to get an owning userns for a superblock] |
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| [[Category: Under the hood]] | | [[Category: Under the hood]] |