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

To: "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, linux-lvm@xxxxxxxxxx
Subject: Bugs in mkfs.xfs, device mapper, xfs, and /dev/ram
From: Spelic <spelic@xxxxxxxxxxxxx>
Date: Thu, 02 Dec 2010 14:55:05 +0100
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100713 Thunderbird/3.0.6
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
(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
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!!

  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@xxxxxxxxxxxxxxx/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.

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