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From db1e692c13290fba4d1c9a5e81b7374c677cb421 Mon Sep 17 00:00:00 2001
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From: Fabian Deutsch <fabiand@fedoraproject.org>
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Date: Wed, 18 Feb 2015 14:31:40 +0100
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Subject: [PATCH] dmsquash: Add rd.live.overlay.thin
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This option changes the underlying mechanism for the overlay in the
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dmsquash module.
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Instead of a plain dm snapshot a dm thin snapshot is used. The advantage
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of the thin snapshot is, that the TRIM command is recognized, which
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means that at runtime, only the occupied blocks will be claimed from
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memory, and freed blocks will really be freed in ram.
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Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>
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(cherry picked from commit d6e34d362a05cda61baaf8e231ad3f0e8665a9cc)
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---
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dracut.cmdline.7.asc | 7 +++++++
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modules.d/90dmsquash-live/dmsquash-live-root.sh | 27 ++++++++++++++++++++++++-
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2 files changed, 33 insertions(+), 1 deletion(-)
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diff --git a/dracut.cmdline.7.asc b/dracut.cmdline.7.asc
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index 0493dcd..0c3bc29 100644
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--- a/dracut.cmdline.7.asc
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+++ b/dracut.cmdline.7.asc
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@@ -802,6 +802,13 @@ Enables debug output from the live boot process.
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Specifies the directory within the squashfs where the ext3fs.img or rootfs.img
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can be found. By default, this is __LiveOS__.
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+**rd.live.overlay.thin=**1::
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+Enables the usage of thin snapshots instead of classic dm snapshots.
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+The advantage of thin snapshots is, that they support discards, and will free
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+blocks which are not claimed by the filesystem. In this use case this means,
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+that memory is given back to the kernel, when the filesystem does not claim it
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+anymore.
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+
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**rd.writable.fsimg=**1::
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Enables writable filesystem support. The system will boot with a fully
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writable filesystem without snapshots __(see notes above about available live boot options)__.
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diff --git a/modules.d/90dmsquash-live/dmsquash-live-root.sh b/modules.d/90dmsquash-live/dmsquash-live-root.sh
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index c6c02c7..0645a0b 100755
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--- a/modules.d/90dmsquash-live/dmsquash-live-root.sh
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+++ b/modules.d/90dmsquash-live/dmsquash-live-root.sh
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@@ -30,6 +30,8 @@ getargbool 0 rd.live.overlay.readonly -d -y readonly_overlay && readonly_overlay
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overlay=$(getarg rd.live.overlay -d overlay)
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getargbool 0 rd.writable.fsimg -d -y writable_fsimg && writable_fsimg="yes"
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+getargbool 0 rd.live.overlay.thin && thin_snapshot="yes"
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+
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# CD/DVD media check
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[ -b $livedev ] && fs=$(blkid -s TYPE -o value $livedev)
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if [ "$fs" = "iso9660" -o "$fs" = "udf" ]; then
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@@ -146,7 +148,30 @@ do_live_overlay() {
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base=$BASE_LOOPDEV
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over=$OVERLAY_LOOPDEV
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fi
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- echo 0 $sz snapshot $base $over p 8 | dmsetup create live-rw
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+ if [ -n "$thin_snapshot" ]; then
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+ modprobe dm_thin_pool
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+ mkdir /run/initramfs/thin-overlay
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+
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+ # In block units (512b)
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+ thin_data_sz=$(( $overlay_size * 1024 * 1024 / 512 ))
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+ thin_meta_sz=$(( $thin_data_sz / 10 ))
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+
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+ # It is important to have the backing file on a tmpfs
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+ # this is needed to let the loopdevice support TRIM
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+ dd if=/dev/null of=/run/initramfs/thin-overlay/meta bs=1b count=1 seek=$((thin_meta_sz)) 2> /dev/null
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+ dd if=/dev/null of=/run/initramfs/thin-overlay/data bs=1b count=1 seek=$((thin_data_sz)) 2> /dev/null
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+
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+ THIN_META_LOOPDEV=$( losetup --show -f /run/initramfs/thin-overlay/meta )
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+ THIN_DATA_LOOPDEV=$( losetup --show -f /run/initramfs/thin-overlay/data )
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+
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+ echo 0 $thin_data_sz thin-pool $THIN_META_LOOPDEV $THIN_DATA_LOOPDEV 1024 1024 | dmsetup create live-overlay-pool
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+ dmsetup message /dev/mapper/live-overlay-pool 0 "create_thin 0"
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+
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+ # Create a snapshot of the base image
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+ echo 0 $sz thin /dev/mapper/live-overlay-pool 0 $base | dmsetup create live-rw
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+ else
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+ echo 0 $sz snapshot $base $over p 8 | dmsetup create live-rw
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+ fi
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# Create a device that always points to a ro base image
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echo 0 $sz linear $base 0 | dmsetup create --readonly live-base
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