linux下对FreeBSD分区读写操作

通常默认的，如果linux内核更新到 kernel 2.6.29, 就已经支持 UFS 文件系统的 写操作了。但是考虑到 危险性操作，一般不会直接就支持写操作。
所以，linux 系统 通常只可以 "只读 " 来挂载 UFS文件系统。

$ sudo mount -t ufs -o ufstype=ufs2 /dev/sdb5 /mnt/
mount: wrong fs type, bad option, bad superblock on /dev/sdb5,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

$ dmesg | tail -n 1
[  871.777769] ufs was compiled with read-only support, can't be mounted as read-write

 为了实现挂载上它，需要专门的 只读 标识:

$ sudo mount -t ufs -o ro,ufstype=ufs2 /dev/sdb2 /mnt/

首先，需要下载当前系统的内核源码，然后复制当前的内核为 .config 

$ sudo -s
# apt-get install linux-source-2.6.27
# cd /usr/src
# bzip2 -dc linux-source-2.6.27.tar.bz2 | tar xf -
# cp /boot/config-2.6.27-2-686 .config

为了增加UFS 写支持到内核，去掉/增加 CONFIG_UFS_WRITE 标识在内核config ，然后从新编译它。

$ grep  CONFIG_UFS_FS_WRITE /usr/src/linux-source-2.6.27/.config
CONFIG_UFS_FS_WRITE=y

To compile my kernel, I followed the instruction here_  . I just added CONCURRENCY_LEVEL=2 to use the 2 cores of my CPU.
编译内核时，可是查看介绍 (followed the instruction here_) ,这里 只是添加 CONCURRENCY_LEVEL=2 来使用 双核 cpu 

$ sudo -s
# CONCURRENCY_LEVEL=2 make-kpkg --initrd --append-to-version=-2-686-ufs kernel-image kernel-headers

一旦编译完成，安装刚刚建立的 内核.(可以在 /usr/src 找到 .deb 文件),然后重启。

$ sudo dpkg -i /usr/src/linux-image-2.6.27-1-686-ufs_2.6.27-1-686-ufs-10.00.Custom_i386.deb 

注意到一些用户：当booting 时有错误，可能时因为忘记了把 initrd  结合到内核中。这时，如果使用的时内核 kernel-package-12.009 (或者更高),确保  来使得 initrd 也同时安装(如果卸载它，删除就可) ：

cp /usr/share/kernel-package/examples/etc/kernel/postinst.d/initramfs /etc/kernel/postinst.d/
cp /usr/share/kernel-package/examples/etc/kernel/postrm.d/initramfs /etc/kernel/postrm.d/

一旦启动了 “UFS-writable”内核，

$ sudo fdisk -l /dev/sdb

Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x8f8000b1

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1        1958    15727603+  83  Linux
/dev/sdb2   *        1959        4569    20972857+  a5  FreeBSD
/dev/sdb3            4570        4830     2096482+  82  Linux swap / Solaris
/dev/sdb4            4831       60801   449587057+  83  Linux

这里，/dev/sdb2 包含了 UFS 文件系统。
如果详细的查看 /dev ，就可以看到所有的信息(当然这里已经执行了"可写")

$ ls -l /dev/sdb*
brw-rw---- 1 root disk 8, 16 2009-04-04 16:20 /dev/sdb
brw-rw---- 1 root disk 8, 17 2009-04-04 14:20 /dev/sdb1
brw-rw---- 1 root disk 8, 18 2009-04-04 16:20 /dev/sdb2  <--- FreeBSD paartition
brw-rw---- 1 root disk 8, 19 2009-04-04 16:20 /dev/sdb3
brw-rw---- 1 root disk 8, 20 2009-04-04 14:20 /dev/sdb4
brw-rw---- 1 root disk 8, 21 2009-04-04 16:20 /dev/sdb5  <--- FreeBSD / slice
brw-rw---- 1 root disk 8, 22 2009-04-04 16:20 /dev/sdb6  <--- FreeBSD swap
brw-rw---- 1 root disk 8, 23 2009-04-04 16:20 /dev/sdb7  <--- FreeBSD /var slice
brw-rw---- 1 root disk 8, 24 2009-04-04 16:20 /dev/sdb8  <--- FreeBSD /tmp slice
brw-rw---- 1 root disk 8, 25 2009-04-04 16:20 /dev/sdb9  <--- FreeBSD /usr slice

Then, I mounted the slices in the right order and to the right mount points (in /mnt/) to have my FreeBSD exact filesystem environment. Then I copied back all the data using the old and nice tar technique, as root:

# ( cd /path/to/backup && tar cpf - . ) | ( cd /mnt/ && tar xvfp - )

Once the "un"-tar was done, I rebooted on my FreeBSD system (from which I am writing this post), forced the fsck of all my slices: everything seems to be OK!

Conclusion

The CONFIG_UFS_FS_WRITE kernel flag is still set as experimental, but it did work like charm for me (using kernel 2.6.27).
If you do use it, and you find a bug, please report it :)

Hope this was helpful.

Cheers,
Ignace M -ghantoos-

Sources

http://www.quietearth.us/articles/2006/09/15/Ubuntu-Compiling-a-custom-kernel




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