dmsquash-live: Support a flattened squashfs.img
A simplified root filesystem structure may be provided for OverlayFS overlays by squashing the root filesystem directly instead of squashing an embedded image file at /LiveOS/rootfs.img. Detect and configure such a squashed root filesystem for live booting. For OverlayFS boots, avoid the read-only Device-mapper linear device at /dev/mapper/live-base. Create a consistent device link at /dev/live-base for the read-only base loop device for all overlayed live root filesystems. Consistently provide a link at /dev/root for wait_for_dev. Update documentation.master
Frederick Grose
Harald Hoyer
parent
e791d753be
commit
789668deb3
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@ -838,23 +838,24 @@ Booting live images
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Dracut offers multiple options for live booted images:
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=====================
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SquashFS with read-only filesystem image::: The system will boot with a read
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only filesystem from the SquashFS and apply a writable device-mapper snapshot
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over the read only filesystem. Using this method ensures a relatively fast
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boot and lower RAM usage. Users **must be careful** to avoid writing too many
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blocks to the snapshot volume. Once the blocks of the snapshot overlay are
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exhausted, the root filesystem becomes read only and may cause application
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failures. The overlay file is marked 'Overflow', and a difficult recovery is
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required to repair and enlarge the overlay offline. Non-persistent overlays
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are sparse files in RAM that only consume content space as required blocks are
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allocated. They default to an apparent size of 32 GiB in RAM. The size can be
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adjusted with the **rd.live.overlay.size=** kernel command line option.
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SquashFS with read-only filesystem image::: The system will boot with a
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read-only filesystem from the SquashFS and apply a writable Device-mapper
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snapshot or an OverlayFS overlay mount for the read-only base filesystem. This
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method ensures a relatively fast boot and lower RAM usage. Users **must be
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careful** to avoid writing too many blocks to a snapshot volume. Once the
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blocks of the snapshot overlay are exhausted, the root filesystem becomes
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read-only and may cause application failures. The snapshot overlay file is
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marked 'Overflow', and a difficult recovery is required to repair and enlarge
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the overlay offline. Non-persistent overlays are sparse files in RAM that only
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consume content space as required blocks are allocated. They default to an
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apparent size of 32 GiB in RAM. The size can be adjusted with the
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**rd.live.overlay.size=** kernel command line option.
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+
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The filesystem structure is expected to be:
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The filesystem structure is traditionally expected to be:
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+
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[listing]
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--
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squashfs.img | Squashfs from LiveCD .iso downloaded via network
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squashfs.img | SquashFS from LiveCD .iso
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!(mount)
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/LiveOS
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|- rootfs.img | Filesystem image to mount read-only
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@ -865,21 +866,35 @@ squashfs.img | Squashfs from LiveCD .iso downloaded via network
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... |
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--
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+
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Dracut uses this method of live booting by default. No additional command line
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options are required other than **root=live:<URL>** to specify the location
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of your squashed filesystem.
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For OverlayFS mount overlays, the filesystem structure may also be a direct
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compression of the root filesystem:
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+
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[listing]
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--
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squashfs.img | SquashFS from LiveCD .iso
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!(mount)
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/bin | Live filesystem
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/boot |
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/dev |
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... |
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--
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+
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Dracut uses one of the overlay methods of live booting by default. No
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additional command line options are required other than **root=live:<URL>** to
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specify the location of your squashed filesystem.
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+
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- The compressed SquashFS image can be copied during boot to RAM at
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`/run/initramfs/squashed.img` by using the **rd.live.ram=1** option.
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- A device with a persistent overlay can be booted read only by using the
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- A device with a persistent overlay can be booted read-only by using the
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**rd.live.overlay.readonly** option on the kernel command line. This will
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cause a temporary, writable overlay to be stacked over a read-only snapshot
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of the root filesystem.
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either cause a temporary, writable overlay to be stacked over a read-only
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snapshot of the root filesystem or the OverlayFS mount will use an additional
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lower layer with the root filesystem.
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+
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Uncompressed live filesystem image:::
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When the live system was installed with the '--skipcompress' option of the
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__livecd-iso-to-disk__ installation script for Live USB devices, the root
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filesystem image, `rootfs.img`, is expanded on installation and no SquashFS
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filesystem image, __rootfs.img__, is expanded on installation and no SquashFS
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is involved during boot.
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+
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- If **rd.live.ram=1** is used in this situation, the full, uncompressed
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@ -887,12 +902,12 @@ root filesystem is copied during boot to `/run/initramfs/rootfs.img` in the
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`/run` tmpfs.
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+
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- If **rd.live.overlay=none** is provided as a kernel command line option,
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a writable, linear device-mapper target is created on boot with no overlay.
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a writable, linear Device-mapper target is created on boot with no overlay.
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writable filesystem image:::
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Writable filesystem image:::
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The system will retrieve a compressed filesystem image, extract it to
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`/run/initramfs/fsimg/rootfs.img`, connect it to a loop device, create a
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writable, linear device-mapper target at `/dev/mapper/live-rw`, and mount that
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writable, linear Device-mapper target at `/dev/mapper/live-rw`, and mount that
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as a writable volume at `/`. More RAM is required during boot but the live
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filesystem is easier to manage if it becomes full. Users can make a filesystem
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image of any size and that size will be maintained when the system boots. There
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@ -902,7 +917,7 @@ The filesystem structure is expected to be:
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+
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[listing]
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--
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rootfs.tgz | Compressed tarball containing fileystem image
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rootfs.tgz | Compressed tarball containing filesystem image
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!(unpack)
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/rootfs.img | Filesystem image at /run/initramfs/fsimg/
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!(mount)
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@ -930,11 +945,11 @@ NOTE: There must be enough free RAM available to hold the complete image.
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This method is very suitable for diskless boots.
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**root=**live:__<url>__::
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Boots a live image retrieved from __<url>__. Requires dracut 'livenet' module.
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Valid handlers: __http, https, ftp, torrent, tftp__.
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Boots a live image retrieved from __<url>__. Requires the dracut 'livenet'
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module. Valid handlers: __http, https, ftp, torrent, tftp__.
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+
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[listing]
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.Example
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.Examples
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--
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root=live:http://example.com/liveboot.img
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root=live:ftp://ftp.example.com/liveboot.img
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@ -946,7 +961,7 @@ Enables debug output from the live boot process.
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**rd.live.dir=**__<path>__::
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Specifies the directory within the boot device where the squashfs.img or
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rootfs.img can be found. By default, this is __LiveOS__.
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rootfs.img can be found. By default, this is `/LiveOS`.
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**rd.live.squashimg=**__<filename of SquashFS image>__::
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Specifies the filename for a SquashFS image of the root filesystem.
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@ -954,35 +969,52 @@ By default, this is __squashfs.img__.
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**rd.live.ram=**1::
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Copy the complete image to RAM and use this for booting. This is useful
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when the image resides on, i.e., a DVD which needs to be ejected later on.
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when the image resides on, e.g., a DVD which needs to be ejected later on.
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**rd.live.overlay={**__<devspec>__[:__{<pathspec>|auto}__]|__none__}::
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Allow the usage of a permanent overlay.
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- _<devspec>_ specifies the path to a device with a mountable filesystem.
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- _<pathspec>_ is the path to a file within that filesystem, which shall be
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Manage the usage of a permanent overlay.
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+
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--
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* _<devspec>_ specifies the path to a device with a mountable filesystem.
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* _<pathspec>_ is the path to a file within that filesystem, which shall be
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used to persist the changes made to the device specified by the
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**root=live:__<url>__** option.
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- _none_ specifies no overlay when an uncompressed live root filesystem is
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available.
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If a persistent overlay is detected at the standard LiveOS path, the overlay &
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overlay type detected (whether Device-mapper or OverlayFS) will be used.
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+
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The default _pathspec_, when _auto_ or no _:<pathspec>_ is given, is
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`/<+++<b>rd.live.dir</b>+++>/overlay-<label>-<uuid>`, where _<label>_ is the
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device LABEL, and _<uuid>_ is the device UUID.
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* _none_ (the word itself) specifies that no overlay will be used, such as when
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an uncompressed, writable live root filesystem is available.
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+
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If a persistent overlay __is detected__ at the standard LiveOS path, the
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overlay & overlay type detected, whether Device-mapper or OverlayFS, will be
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used.
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--
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+
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[listing]
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.Example
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.Examples
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--
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rd.live.overlay=/dev/sdb1:persistent-overlay.img
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rd.live.overlay=UUID=99440c1f-8daa-41bf-b965-b7240a8996f4
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--
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**rd.live.overlay.size=**__<size_MiB>__::
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Specifies a non-persistent overlay size in MiB. The default is _32768_.
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Specifies a non-persistent Device-mapper overlay size in MiB. The default is
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_32768_.
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**rd.live.overlay.readonly=**1::
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Specifies a non-persistent, writable snapshot overlay to be stacked over a
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read-only snapshot of the root filesystem, `/dev/mapper/live-ro`, or a read-
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only loop device of a writable `rootfs.img`.
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This is used to boot with a normally read-write persistent overlay in a
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read-only mode. With this option, either an additional, non-persistent,
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writable snapshot overlay will be stacked over a read-only snapshot,
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`/dev/mapper/live‑ro`, of the base filesystem with the persistent overlay, or a
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read-only loop device, in the case of a writable __rootfs.img__, or an OverlayFS
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mount will use the persistent overlay directory linked at `/run/overlayfs‑r` as
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an additional lower layer along with the base root filesystem and apply a
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transient, writable upper directory overlay, in order to complete the booted
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root filesystem.
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**rd.live.overlay.reset=**1::
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Specifies that a persistent overlay should be reset on boot. All root
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Specifies that a persistent overlay should be reset on boot. All previous root
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filesystem changes are vacated by this action.
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**rd.live.overlay.thin=**1::
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@ -993,25 +1025,25 @@ that memory is given back to the kernel when the filesystem does not claim it
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anymore.
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**rd.live.overlay.overlayfs=**1::
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Enables the use of the **OverlayFS** kernel module, if available, to provide a
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Enables the use of the *OverlayFS* kernel module, if available, to provide a
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copy-on-write union directory for the root filesystem. OverlayFS overlays are
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directories of the files that have changed on the read-only base (lower)
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filesystem. The root filesystem is provided through a special overlay type
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mount that merges the lower and upper directories. If an OverlayFS upper
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directory is not present on the boot device, a tmpfs directory will be created
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at /run/overlayfs to provide temporary storage. Persistent storage can be
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at `/run/overlayfs` to provide temporary storage. Persistent storage can be
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provided on vfat or msdos formatted devices by supplying the OverlayFS upper
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directory within an embedded filesystem that supports the creation of trusted.*
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extended attributes and provides a valid d_type in readdir responses, such as
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with ext4 and xfs. On non-vfat-formatted devices, a persistent OverlayFS
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overlay can extend the available root filesystem storage up to the capacity of
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the LiveOS device.
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the LiveOS disk device.
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+
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If a persistent overlay is detected at the standard LiveOS path, the overlay &
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overlay type detected (whether OverlayFS or Device-mapper) will be used.
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overlay type detected, whether OverlayFS or Device-mapper, will be used.
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+
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The **rd.live.overlay.readonly** option, which allows a persistent overlayfs to
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be mounted read only through a higher level transient overlay directory, has
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be mounted read-only through a higher level transient overlay directory, has
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been implemented through the multiple lower layers feature of OverlayFS.
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@ -250,13 +250,11 @@ do_live_overlay() {
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echo 0 $sz snapshot $base $over PO 8 | dmsetup create live-rw
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fi
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# Create a device that always points to a ro base image
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if [ -n "$overlayfs" ]; then
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BASE_LOOPDUP=$(losetup -f --show -r $BASE_LOOPDEV)
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echo 0 $sz linear $BASE_LOOPDUP 0 | dmsetup create --readonly live-base
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else
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# Create a device for the ro base of overlayed file systems.
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if [ -z "$overlayfs" ]; then
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echo 0 $sz linear $BASE_LOOPDEV 0 | dmsetup create --readonly live-base
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fi
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ln -s $BASE_LOOPDEV /dev/live-base
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}
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# we might have a genMinInstDelta delta file for anaconda to take advantage of
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@ -291,10 +289,21 @@ if [ -e "$SQUASHED" ]; then
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mkdir -m 0755 -p /run/initramfs/squashfs
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mount -n -t squashfs -o ro $SQUASHED_LOOPDEV /run/initramfs/squashfs
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if [ -f /run/initramfs/squashfs/LiveOS/rootfs.img ]; then
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FSIMG="/run/initramfs/squashfs/LiveOS/rootfs.img"
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elif [ -f /run/initramfs/squashfs/LiveOS/ext3fs.img ]; then
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FSIMG="/run/initramfs/squashfs/LiveOS/ext3fs.img"
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if [ -d /run/initramfs/squashfs/LiveOS ]; then
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if [ -f /run/initramfs/squashfs/LiveOS/rootfs.img ]; then
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FSIMG="/run/initramfs/squashfs/LiveOS/rootfs.img"
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elif [ -f /run/initramfs/squashfs/LiveOS/ext3fs.img ]; then
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FSIMG="/run/initramfs/squashfs/LiveOS/ext3fs.img"
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fi
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elif [ -d /run/initramfs/squashfs/proc ]; then
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FSIMG=$SQUASHED
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if [ -z "$overlayfs" ]; then
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overlayfs="yes"
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[ -n "$DRACUT_SYSTEMD" ] && reloadsysrootmountunit="yes"
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fi
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else
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die "Failed to find a root filesystem in $SQUASHED."
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exit 1
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fi
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else
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# we might have an embedded fs image to use as rootfs (uncompressed live)
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@ -312,8 +321,8 @@ else
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fi
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fi
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if [ -n "$FSIMG" ] ; then
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if [ -n "$writable_fsimg" ] ; then
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if [ -n "$FSIMG" ]; then
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if [ -n "$writable_fsimg" ]; then
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# mount the provided filesystem read/write
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echo "Unpacking live filesystem (may take some time)" > /dev/kmsg
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mkdir -m 0755 /run/initramfs/fsimg/
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@ -336,9 +345,13 @@ if [ -n "$FSIMG" ] ; then
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setup=yes
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fi
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fi
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BASE_LOOPDEV=$(losetup -f --show $opt $FSIMG)
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sz=$(blockdev --getsz $BASE_LOOPDEV)
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if [ "$setup" == rw ]; then
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if [ "$FSIMG" = "$SQUASHED" ]; then
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BASE_LOOPDEV=$SQUASHED_LOOPDEV
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else
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BASE_LOOPDEV=$(losetup -f --show $opt $FSIMG)
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sz=$(blockdev --getsz $BASE_LOOPDEV)
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fi
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if [ "$setup" = rw ]; then
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echo 0 $sz linear $BASE_LOOPDEV 0 | dmsetup create live-rw
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else
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# Add a DM snapshot or OverlayFS for writes.
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@ -346,8 +359,6 @@ if [ -n "$FSIMG" ] ; then
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fi
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fi
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[ -e "$SQUASHED" ] && [ -z "$overlayfs" ] && umount -l /run/initramfs/squashfs
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if [ -b "$OSMIN_LOOPDEV" ]; then
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# set up the devicemapper snapshot device, which will merge
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# the normal live fs image, and the delta, into a minimzied fs image
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@ -380,17 +391,17 @@ if [ -n "$overlayfs" ]; then
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'lowerdir=/run/rootfsbase,upperdir=/run/overlayfs,workdir=/run/ovlwork' \
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"$NEWROOT" > $hookdir/mount/01-$$-live.sh
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fi
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_dev=/run/rootfsbase
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else
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_dev=/dev/mapper/live-rw
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if [ -z "$DRACUT_SYSTEMD" ]; then
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[ -n "$ROOTFLAGS" ] && ROOTFLAGS="-o $ROOTFLAGS"
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printf 'mount %s /dev/mapper/live-rw %s\n' "$ROOTFLAGS" "$NEWROOT" > $hookdir/mount/01-$$-live.sh
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fi
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ln -s $BASE_LOOPDEV /run/rootfsbase
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fi
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ln -s $_dev /dev/root
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[ -e "$SQUASHED" ] && umount -l /run/initramfs/squashfs
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ln -s null /dev/root
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need_shutdown
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exit 0
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Loading…
Reference in New Issue