Bugs in mkfs.xfs, device mapper, xfs, and /dev/ram

Spelic
2010-12-02T13:54:58Z

Hello all

I noticed what seem to be 4 bugs.
(kernel v2.6.37-rc4 but probably also before)

First two are one in mkfs.xfs and one in device mapper (lvm mailing list
I suppose, otherwise pls forward it):

Steps to reproduce:

Boot with a large ramdisk, like ramdisk_size=2097152
(actually I had 14GB ramdisk when I tried this but I don't think it will
make a difference)

Now partition it with a 1GB partition:
fdisk /dev/ram0
n
p
1
1
+1G
w
(only one 1GB physical partition)

Make a devmapper mapping for the partition
kpartx -av /dev/ram0

mkfs.xfs -f /dev/mapper/ram0p1
meta-data=/dev/mapper/ram0p1 isize=256 agcount=4,
agsize=66266 blks
= sectsz=512 attr=2
data = bsize=4096 blocks=265064, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0
log =internal log bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0

Now, lo and behold, partition is gone!
fdisk /dev/ram0
p
will show no partitions!

you can also check with
dd if=/dev/ram bs=1M count=1 | hexdump -C
All first MB of /dev/ram is zeroed!!

also
mount /dev/ram0p1 /mnt
will fail. Unknown filesystem

I think this shows 2 bugs: firstly mkfs.xfs dares to do stuff before the
beginning of the device on which it should work.
Secondly, device mapper does not constrain access within the boundaries
of the device, which I think it should do.

Then I have 2 more bugs for you. Please see my thread in linux-rdma called:
"NFS-RDMA hangs: connection closed (-103)"
in particular this post
http://www.mail-archive.com/linux-rdma@vger.kernel.org/msg06632.html
with NFS over <RDMA or IPoIB> over Infiniband over XFS over ramdisk it
is possible to write a file (2.3GB) which is larger than the size of the
device (1.5GB): one bug I think is for XFS people (because I think XFS
should check if the space on the filesystem is finished), and another
one I think is for /dev/ram people (what mailing list? I am adding
lkml), because I think the device should check if someone is writing
beyond the end of it.

Thank you
PS: I am not subscribed to lkml so please do not reply ONLY to lkml.