Add ephemeral state to mount fs without altering fstab #264

NeodymiumFerBore · 2021-09-12T21:07:20Z

SUMMARY

Add ephemeral possible value for state parameter.

The ephemeral state allows end-users to mount a volume on a given path, without altering an fstab file or creating a dummy one.

There have been debates about splitting this module into an fstab module and a mount module, but nothing has been done in 5 years. This is why I'd like to propose this feature.

Downside: the way the posix.mount module handles the mount options prevent it to be able to check exactly if the given opts perfectly match the mount options of an already mounted volume. To achieve this, the module would have to be aware of every mount default options, for all platforms. This is why the ephemeral state always return changed=yes. In other terms, a remount will always be triggered if the volume is already mounted, even if the options look to be the same. However, using state unmounted on a volume previously mounted with ephemeral behaves correctly.

ISSUE TYPE

Feature Pull Request

Related issues:

COMPONENT NAME

mount

ADDITIONAL INFORMATION

Example use case

Sometimes it is handy to be able to temporarily mount a volume. I've seen this in some companies where they use Ansible to generate reports and put it on network shares. However, some admins don't look into mount options such as krb5 and multiuser for SMB shares. Being forced to use fstab-based mounts leads to clear text passwords being stored more or less temporarily on the host filesystem, requiring "manual" deletion (with the hassle of using blocks, rescues, always, etc.). This feature respond to this use case by providing a way to mount a volume without having to alter an fstab file.

Description of changes

Edit DOCUMENTATION section to add ephemeral state
Edit EXAMPLES section to add ephemeral state example
Add new function _set_ephemeral_args to use instead of _set_fstab_args when using ephemeral state
Add new function _is_same_mount_src to determine if the mounted volume on the destination path has the same source than the one supplied to the module
Add new function _get_mount_info to avoid redundant code between functions get_linux_mounts and _is_same_mount_src
Modify get_linux_mount to use the new function _get_mount_info. Behavior is preserved.
Integrate ephemeral parameter treatment into mounted treatment, and add if statements to avoid IO from/to fstab
Add ephemeral as a possible value for the state parameter in main()
Add required_if dependencies for ephemeral state

- Edit DOCUMENTATION section to add ephemeral state - Edit EXAMPLES section to add ephemeral state example - Add new function `_set_ephemeral_args` to replace `_set_fstab_args` when using ephemeral state - Add new function `_is_same_mount_src` to determine if the mounted volume on the destination path has the same source than the one supplied to the module - Add new function `_get_mount_info` to avoid redundant code between functions `get_linux_mounts` and `_is_same_mount_src` - Modify `get_linux_mount` to use the new function `_get_mount_info`. Behavior is preserved. - Integrate `ephemeral` parameter treatment into `mounted` treatment, and add `if` statements to avoid IO from/to fstab - Add `ephemeral` as a possible value for the `state` parameter in `main()` - Add `required_if` dependencies for `ephemeral` state

NeodymiumFerBore

Added comments on major modifications in mount.py.

NeodymiumFerBore · 2021-09-12T21:37:16Z

plugins/modules/mount.py

+    path: /mnt/smb_share
+    opts: "rw,vers=3,file_mode=0600,dir_mode=0700,dom={{ ad_domain }},username={{ ad_username }},password={{ ad_password }}"
+    fstype: cifs
+    state: ephemeral


Examples: add an example for the use of state=ephemeral. This example has been tested on my side.

NeodymiumFerBore · 2021-09-12T21:40:30Z

plugins/modules/mount.py

@@ -426,6 +443,23 @@ def _set_fstab_args(fstab_file):
    return result


+def _set_ephemeral_args(args):


_set_ephemeral_args(args): When using ephemeral, we cannot rely on an fstab entry to set the mount options. This function sets the mount options accordingly to what was supplied to the module: fstype, opts and src.

NeodymiumFerBore · 2021-09-12T21:48:10Z

plugins/modules/mount.py

-    """Gather mount information"""
-
+def _get_mount_info(module, mntinfo_file="/proc/self/mountinfo"):
+    """Return raw mount information"""


New function _get_mount_info and minor change in function get_linux_mounts. As my new function _is_same_mount_src uses the mount info, I created this new function to avoid code redundancy. The function get_linux_mounts has been edited accordingly, and the original behavior is entirely preserved.

This function does exactly what get_linux_mounts used to do to retrieve mount info.

NeodymiumFerBore · 2021-09-12T21:50:02Z

plugins/modules/mount.py

+    # Keep same behavior than before
+    if lines is None:
+        return
+


The condition if lines is None: return preserve the function behavior from before the edit.

NeodymiumFerBore · 2021-09-12T21:50:18Z

plugins/modules/mount.py

+    return lines
+
+
+def get_linux_mounts(module, mntinfo_file="/proc/self/mountinfo"):


As previously noticed, this function has been edited to use the new function _get_mount_info, instead of retrieving "manually" the mount info.

NeodymiumFerBore · 2021-09-12T21:55:09Z

plugins/modules/mount.py

@@ -659,6 +709,24 @@ def get_linux_mounts(module, mntinfo_file="/proc/self/mountinfo"):
    return mounts


+def _is_same_mount_src(module, args, mntinfo_file="/proc/self/mountinfo"):
+    """Return True if the mounted fs on mountpoint is the same source than src"""


New function _is_same_mount_src: This function is used for the ephemeral state: if this function returns False, then it means that the provided mount point has already a volume mounted on it, which is NOT the volume given in src. This leads to a module failure, to avoid an unwanted unmount.

NeodymiumFerBore · 2021-09-12T21:59:58Z

plugins/modules/mount.py

+
+    for line in lines:
+        fields = line.split()
+        if fields[4] == mountpoint and fields[-2] == src:


fields[4] contains a mountpoint and fields[-2] contains the associated source. See get_linux_mounts for more info about mountinfo fields. The logic behind picking these fields was already implemented, I only copy-pasted after test and review.

NeodymiumFerBore · 2021-09-12T22:02:56Z

plugins/modules/mount.py

-        except Exception as e:
-            module.fail_json(msg="Failed to open %s due to %s" % (args['fstab'], to_native(e)))
+    # If state is 'ephemeral', we do not need fstab file
+    if module.params['state'] != 'ephemeral':


Only this line changed (add if statement and fix block indent). This code block is in charge of creating the provided fstab file. For ephemeral state, the fstab file does not have to be created.

NeodymiumFerBore · 2021-09-12T22:04:10Z

plugins/modules/mount.py

@@ -797,7 +870,7 @@ def main():
                        msg="Error unmounting %s: %s" % (name, msg))

            changed = True
-    elif state == 'mounted':
+    elif state == 'mounted' or state == 'ephemeral':


ephemeral treatment is based on the mounted logic, bypassing the fstab read and write.

NeodymiumFerBore · 2021-09-12T22:10:05Z

plugins/modules/mount.py

+                            'unwanted unmount or override operation. Try replacing this command with '
+                            'a "state: unmounted" followed by a "state: ephemeral", or use '
+                            'a different destination path.'))
+


When state is ephemeral or mounted, it tests if the provided mountpoint has already a volume mounted on it.

In the case of ephemeral, there is no fstab file to provide an authoritative answer to the question "What should be mounted here". To avoid an unwanted unmount and a possible service outage, the module fails if the volume already mounted on the mountpoint is not the same as the one provided in src (this is checked with the new function _is_same_mount_src).

NeodymiumFerBore · 2021-09-14T17:13:10Z

Renaming the branch closed the pull request. I thought the PR would be relocated, but this only works the other way around... Sorry for that. New PR: #267

NeodymiumFerBore and others added 3 commits September 12, 2021 22:41

Add changelog fragment for ephemeral mount state

c458204

Fix wrong PR URL in changelog fragment

d218c37

NeodymiumFerBore commented Sep 12, 2021

View reviewed changes

NeodymiumFerBore added 2 commits September 13, 2021 00:32

Add blank lines to respect linter policy

c4b3678

Pass mntinfo_file to _get_mount_info to avoid possible future code break

53a10bd

NeodymiumFerBore closed this Sep 13, 2021

NeodymiumFerBore deleted the patch-1 branch September 13, 2021 21:08

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Add ephemeral state to mount fs without altering fstab #264

Add ephemeral state to mount fs without altering fstab #264

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NeodymiumFerBore commented Sep 14, 2021

		@@ -426,6 +443,23 @@ def _set_fstab_args(fstab_file):
		return result


		def _set_ephemeral_args(args):

		return lines


		def get_linux_mounts(module, mntinfo_file="/proc/self/mountinfo"):

Add ephemeral state to mount fs without altering fstab #264

Add ephemeral state to mount fs without altering fstab #264

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NeodymiumFerBore commented Sep 12, 2021 • edited Loading

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NeodymiumFerBore commented Sep 14, 2021

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