Squashfs support for MTD subsystem - Revision history

Vapier: obsoleted by another proposal ?

2011-03-22T23:23:38Z

obsoleted by another proposal ?

Plougher at 21:02, 31 January 2011

2011-01-31T21:02:30Z

Wmat: Added body of squashfs support for MTD subsystem

2011-01-31T20:54:47Z

Added body of squashfs support for MTD subsystem

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Squashfs support for MTD subsystem

; Summary: Squashfs support for MTD subsystem

; Proposer: Phillip Lougher

== Description ==
This proposal will add MTD subsystem support to Squashfs,
including bad block handling.

Squashfs is already widely used on MTD devices (NAND flash etc.)
in embedded systems, however, because Squashfs lacks native MTD support,
this is currently performed via MTD's block device emulation (or via UBI
or stored inside another MTD aware filesystem, i.e. YAFFS2/JFFS2).
These solutions add unnecessary code and run-time overhead, and in the
case of MTD's block device emulation, this lacks bad block support.

The following two tasks will be undertaken:

* Write a user-space utility that writes Squashfs filesystems to NAND, skipping bad
blocks (and record that bad bocks have been skipped in the out of band data).

* Re-write the low-level squashfs_read_data() routine in the kernel squashfs code to
read directly from NAND using MTD. This will use the out of band data to determine
which blocks have been skipped by the user-space utility.

It is anticipated that a major piece of the work will be the
refactoring of the squashfs_read_data() function and I/O backend
in such a way that MTD support is added cleanly, minimising changes
to existing critical code and without affecting performance.

== Related work ==
* http://thread.gmane.org/gmane.linux.kernel/962226

Added MTD handling to Squashfs, without any bad block handling.
Unfortunately, I (the Squashfs maintainer) considered the
patch series to be overly complicated, it unnecessarily
touched too much core code, and removed many performance
optimisations (see http://article.gmane.org/gmane.linux.kernel/965490).

== Scope ==
About 2 months

== Contractor Candidates ==
I'm recommending myself, as the author and maintainer of
Squashfs.

== Comments ==

[[Category:Project proposals 2011]]

← Older revision		Revision as of 23:23, 22 March 2011
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	== Comments ==		== Comments ==
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		+	Isn't this obsoleted by [[Support read-only block filesystems on MTD flash]]?

	[[Category:Project proposals 2011]]		[[Category:Project proposals 2011]]

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 The following two tasks will be undertaken:
-* Write a user-space utility that writes Squashfs filesystems to NAND, skipping bad
+* Write a user-space utility that writes Squashfs filesystems to NAND, skipping bad blocks (and record that bad bocks have been skipped in the out of band data).
 blocks (and record that bad bocks have been skipped in the out of band data).
-* Re-write the low-level squashfs_read_data() routine in the kernel squashfs code to
+* Re-write the low-level squashfs_read_data() routine in the kernel squashfs code to read directly from NAND using MTD.  This will use the out of band data to determine which blocks have been skipped by the user-space utility.
 read directly from NAND using MTD.  This will use the out of band data to determine
 which blocks have been skipped by the user-space utility.
 It is anticipated that a major piece of the work will be the