[PATCH] mount udf UDF_PART_FLAG_READ_ONLY partitions with MS_RDONLY

There's a bug where a UDF_PART_FLAG_READ_ONLY udf partition gets mounted
read-write, then subsequent problems happen; files seem to be able to be
removed, but file creation results in EIO or worse, oops.

EIO is coming from udf_new_block(), which returns EIO if the right flags
aren't set; only UDF_PART_FLAG_READ_ONLY is set in this case.  We probably
s hould not have gotten this far...

Attached patch seems to fix it - and includes a printk to alert the user
that their "rw" mount request has been converted to "ro."

Here's the testcase I used:

[root@magnesium ~]# mkisofs -R -J -udf -o testiso /tmp/
...
Total translation table size: 0
Total rockridge attributes bytes: 342923
Total directory bytes: 382312
Path table size(bytes): 104
Max brk space used 103000
105059 extents written (205 MB)

[root@magnesium ~]# mount -o loop testiso /mnt/test/
[root@magnesium ~]# ls /mnt/test/fsfile
/mnt/test/fsfile
[root@magnesium ~]# rm /mnt/test/fsfile
[root@magnesium ~]# ls /mnt/test/fsfile
ls: /mnt/test/fsfile: No such file or directory
[root@magnesium ~]# touch /mnt/test/fsfile
touch: cannot touch `/mnt/test/fsfile': Input/output error
[root@magnesium tmp]# grep udf /proc/mounts
/dev/loop1 /mnt/test udf rw 0 0

Force readonly mounts of UDF partitions marked as read-only.

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>