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config: clarify Linux mount options #1181

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config: clarify Linux mount options #1181

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81 changes: 79 additions & 2 deletions config.md
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Expand Up @@ -77,11 +77,87 @@ For Solaris, the mount entry corresponds to the 'fs' resource in the [zonecfg(1M
* Windows: a local directory on the filesystem of the container host. UNC paths and mapped drives are not supported.
* Solaris: corresponds to "special" of the fs resource in [zonecfg(1M)][zonecfg.1m].
* **`options`** (array of strings, OPTIONAL) Mount options of the filesystem to be used.
* Linux: supported options are listed in the [mount(8)][mount.8] man page.
Note both [filesystem-independent][mount.8-filesystem-independent] and [filesystem-specific][mount.8-filesystem-specific] options are listed.
* Linux: See [Linux mount options](#configLinuxMountOptions) below.
* Solaris: corresponds to "options" of the fs resource in [zonecfg(1M)][zonecfg.1m].
* Windows: runtimes MUST support `ro`, mounting the filesystem read-only when `ro` is given.

### <a name="configLinuxMountOptions" />Linux mount options

Runtimes MUST/SHOULD/MAY implement the following option strings for Linux:

Option name | Requirement | Description
------------------|-------------|-----------------------------------------------------
`async` | MUST | [^1]
`atime` | MUST | [^1]
`bind` | MUST | [^2] (bind mounts)
`defaults` | MUST | [^1]
`dev` | MUST | [^1]
`diratime` | MUST | [^1]
`dirsync` | MUST | [^1]
`exec` | MUST | [^1]
`iversion` | MUST | [^1]
`lazytime` | MUST | [^1]
`loud` | MUST | [^1]
`mand` | MAY | [^1] (Deprecated in kernel 5.15, util-linux 2.38)
`noatime` | MUST | [^1]
`nodev` | MUST | [^1]
`nodiratime` | MUST | [^1]
`noexec` | MUST | [^1]
`noiversion` | MUST | [^1]
`nolazytime` | MUST | [^1]
`nomand` | MAY | [^1]
`norelatime` | MUST | [^1]
`nostrictatime` | MUST | [^1]
`nosuid` | MUST | [^1]
`nosymfollow` | SHOULD | [^1] (Introduced in kernel 5.10, util-linux 2.38)
`private` | MUST | [^2] (bind mounts)
`ratime` | SHOULD | Recursive `atime` [^3]
`rbind` | MUST | [^2] (bind mounts)
`rdev` | SHOULD | Recursive `dev` [^3]
`rdiratime` | SHOULD | Recursive `diratime` [^3]
`relatime` | MUST | [^1]
`remount` | MUST | [^1]
`rexec` | SHOULD | Recursive `dev` [^3]
`rnoatime` | SHOULD | Recursive `noatime` [^3]
`rnodiratime` | SHOULD | Recursive `nodiratime` [^3]
`rnoexec` | SHOULD | Recursive `noexec` [^3]
`rnorelatime` | SHOULD | Recursive `norelatime` [^3]
`rnostrictatime` | SHOULD | Recursive `nostrictatime` [^3]
`rnosuid` | SHOULD | Recursive `nosuid` [^3]
`rnosymfollow` | SHOULD | Recursive `nosymfollow` [^3]
`ro` | MUST | [^1]
`rprivate` | MUST | [^2] (bind mounts)
`rrelatime ` | SHOULD | Recursive `relatime` [^3]
`rro` | SHOULD | Recursive `ro` [^3]
`rrw` | SHOULD | Recursive `rw` [^3]
`rshared` | MUST | [^2] (bind mounts)
`rslave` | MUST | [^2] (bind mounts)
`rstrictatime` | SHOULD | Recursive `strictatime` [^3]
`rsuid` | SHOULD | Recursive `suid` [^3]
`rsymfollow` | SHOULD | Recursive `symfollow` [^3]
`runbindable` | MUST | [^2] (bind mounts)
`rw` | MUST | [^1]
`shared` | MUST | [^1]
`silent` | MUST | [^1]
`slave` | MUST | [^2] (bind mounts)
`strictatime` | MUST | [^1]
`suid` | MUST | [^1]
`symfollow` | SHOULD | Opposite of `nosymfollow`
`sync` | MUST | [^1]
`tmpcopyup` | MAY | copy up the contents to a tmpfs
`unbindable` | MUST | [^2] (bind mounts)

[^1]: Corresponds to [`mount(8)` (filesystem-independent)][mount.8-filesystem-independent].
[^2]: Corresponds to [`mount(8)` (filesystem-specific)][mount.8-filesystem-specific].
[^3]: These `AT_RECURSIVE` options need kernel 5.12 or later. See [`mount_setattr(2)`][mount_setattr.2]

The "MUST" options correspond to [`mount(8)`][mount.8].

Runtimes MAY also implement custom option strings that are not listed in the table above.
If a custom option string is already recognized by [`mount(8)`][mount.8], the runtime SHOULD follow the behavior of [`mount(8)`][mount.8].

Runtimes SHOULD pass unknown options to [`mount(2)`][mount.2] via the fifth argument (`const void *data`).

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(The list of the implemented options is printed in runc features)

### Example (Windows)

```json
Expand Down Expand Up @@ -1004,6 +1080,7 @@ Here is a full example `config.json` for reference.
[mount.8]: http://man7.org/linux/man-pages/man8/mount.8.html
[mount.8-filesystem-independent]: http://man7.org/linux/man-pages/man8/mount.8.html#FILESYSTEM-INDEPENDENT_MOUNT_OPTIONS
[mount.8-filesystem-specific]: http://man7.org/linux/man-pages/man8/mount.8.html#FILESYSTEM-SPECIFIC_MOUNT_OPTIONS
[mount_setattr.2]: http://man7.org/linux/man-pages/man2/mount_setattr.2.html
[getrlimit.2]: http://man7.org/linux/man-pages/man2/getrlimit.2.html
[getrlimit.3]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/getrlimit.html
[stdin.3]: http://man7.org/linux/man-pages/man3/stdin.3.html
Expand Down