Ext2fs 0.6alpha2 Release

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An alpha-level patch for Ext2fs is now available on tsx-11.mit.edu in /pub/linux/ALPHA/ext2fs/linux-2.1.36-ext2fs-0.6alpha2.diff.gz.

This patch adds new features to Ext2fs and fixes a few problem. Here is a list of these changes :

• New mount options are supported:
  • readuid=<uid>, readgid=<gid>, writeuid=<uid>, writegid=<gid>
    Allow the administrator to specify a user or a group that has read or write access on every file on the filesystem. I know that this should be acomplished by using Posix.6 priviledges but some people have been asking for these options that can be useful until Posix.6 is implemented in the Linux kernel.

  • umap=<uid-mapping-file-name>, gmap=<gid-mapping-file-name>
    Allow the administrator to specify mapping files: these files are used to convert uid and/or gid when using a filesystem that comes from a foreign system. Each line of a map file should contain two numerical values: the original id (i.e. the id used on the filesystem) and the new id (i.e. the id used on the local system). When reading an inode into memory, original ids are converted to new ones. When writing an inode to disk, new ids are converted to original ones.

• 32-bits ids and 64-bits device numbers are supported:
  Ext2fs now stores uids and gids as 32-bits quantities and device numbers as 64-bits quantities, on the disk. If 32-bits ids and/or 64-bits device numbers ever get supported in the other parts of the kernel, no change in Ext2fs will be needed.

• A new unlink implementation is in:
  Previous versions of Ext2fs implemented unlink() by setting the file size to 0 and by calling truncate(). This had some nasty consequences:
  • the block addresses contained in indirect blocks were zeroed when removing a file, so it was difficult to recover files,
  • the secure deletion feature had been deactivated because of a conflict with the virtual memory management code.

    The new implementation fixes these problems and is 45% faster than the previous one.

• Minor bugs have been fixed.

• Minor optimizations have been integrated.

• Unfortunately, a few fields have been renamed so the patch breaks the compilation of e2fsprogs (but already-compiled e2fsprogs work like a charm).

This patch does *not* contain the changes that Ted Ts'o has sent to this list on Saturday 26th. Since I expect that Ted's changes will be part of the next kernel version, I will make another patch against 2.1.37 when it is available (watch /pub/linux/ALPHA/ext2fs on tsx-11 when 2.1.37 is released).

I remind you that this is an alpha-level patch. This means that it has not been heavlily tested and it may cause problems on filesystems. Don't use it if you don't consider yourself as a brave tester :-)

I plan to release some other patches in a near future. Ext2fs 0.6 alpha3 will contain Posix.6 ACL support and will be available in a few weeks.