Add Read-Only Btrfs Snapshots Option (issue #332)

[CloverGit]

Adds an option to create read-only Btrfs snapshots by default. Resolves #332

[ygerlach]

Do we need a warning if someone tries to use --readonly in an rsync setup?

[CloverGit]

The shell argument description already clarifies that this feature is specifically for Btrfs, and I believe that users familiar with rsync will understand that it doesn't have a "read-only" concept. However, if necessary, perhaps consider changing the argument name to '--btrfs-readonly'?

[cshandley-uk]

Please do NOT make snapshots read-only, as this will basically break "grub-btrfs", and prevent the ability to boot into a snapshot. Or if you DO make them read-only, then there should be a separate set of snapshots that are read-write, but I think that would be over-complicating things. At best make this change optional please.

[agusdmb]

Please do NOT make snapshots read-only, as this will basically break "grub-btrfs", and prevent the ability to boot into a snapshot. Or if you DO make them read-only, then there should be a separate set of snapshots that are read-write, but I think that would be over-complicating things. At best make this change optional please.

i think having it optional would be ideal

[CloverGit]

Please do NOT make snapshots read-only, as this will basically break "grub-btrfs", and prevent the ability to boot into a snapshot. Or if you DO make them read-only, then there should be a separate set of snapshots that are read-write, but I think that would be over-complicating things. At best make this change optional please.

I agree with making it optional, but I still recommend keeping read-only as the default behavior, a "writable snapshot" contradicts the design purpose of snapshot (frozen disk state).
For read-only snapshots, you should use grub-btrfs-overlayfs instead of grub-btrfs.

[ygerlach]

One can always change the "read-only-nes" of a snapshot by either

• creating a new writeable snapshot of the given read-only snapshot (btrfs subvolume snapshot /path/to/snapshot /path/to/snapshot_rw
  or
• actually changing the flag btrfs property set -ts /path/to/snapshot ro false

I think having an option to set the value for all new snapshots (default to ro) and having the option to toggle a snapshot with the context menu would be the best option for everybody.
Users often booting into snapshots can set the default to be writable and other users are protected against accidentally destroying their snapshots, but still have the option to edit a snapshot for what ever reason they may need.

At best make this change optional please.

commit 797d8c2 makes it an option in the settings.