[archiso] Allow persistent cow dm-snapshots.

Add some options to control where all COW files will be located.
Until this moment all files are located in a tmpfs filesystem.
Now is posible to set a device via a filesystem label or device node
plus a directory, where all these files will be stored.
All dm-snapshot devices will be persistent by default,
but this can be changed if wanted.

Take care, a filesystem that does not support sparse files maybe
is not the best choice for COW files, because they are created with
the same size (is apparent) like the read-only device (the image.fs inside .sfs).
Of course sooner or later, depending on use, these files actually end up
being as big as the read-only device.

KNOW-ISSUE: On shutdown in step "Unmounting Filesystems" will [FAIL],
    all filesystem except $cow_device, will be unmounted/remounted-ro.
    For this reason this change needs an archiso_shutdown hook, thats
    unmount all block devices used by archiso. (Work in progress)

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

1 files changed, 10 insertions, 0 deletions

diff --git a/README b/README
index 9c49946..8f59be3 100644
--- a/README
+++ b/README
@@ -35,6 +35,16 @@ INDEX
                     performs a self-test of all files inside ${install_dir},
                     and continue booting if ok.
                     Default: (unset)
+* cow_label=        Set the filesystem label where COW (dm-snapshot)
+                    files must be stored.
+                    Default: (unset)
+* cow_device=       Set the device node where COW (dm-snapshot) files
+                    must be stored.
+                    Default: (unset) or "/dev/disk/by-label/${cow_label}"
+* cow_directory=    Set a directory inside ${cow_device}.
+                    Default: "/persistent_${archisolabel}/${arch}"
+* cow_persistent=   Set if snapshots are persistent "P" or non-persistent "N".
+                    Default: "N" (if no ${cow_device} is used) otherwise "P".
 * cowspace_size=    Set the size of tmpfs /cowspace. This space is used for
                     Copy-On-Write files of dm-snapshot.
                     (directory not visible outside initramfs)