2.6.28-rc3: kernel mounts the same device twice? Or /proc/mounts lies?

2.6.28-rc3: kernel mounts the same device twice? Or /proc/mounts lies?

[Andrey Borzenkov]

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Out of some infinite wisdom something on my system decided to add
fstab entry for "new" device after switching from IDE to PATA:

# Entry for /dev/LABEL=/ :
LABEL=/ / reiserfs relatime,tail 1 1
none /proc proc defaults 0 0
none /sys sysfs defaults 0 0
none /tmp tmpfs defaults 0 0
# Entry for /dev/LABEL=swap :
LABEL=swap swap swap defaults 0 0
# Entry for /dev/sda2 :
UUID=72973377-c299-4ca6-ae94-2022b7dca58f /media/hd reiserfs defaults 0 0

Note that both / and /media/hd refer to the same device:

{pts/0}% sudo blkid
/dev/sda1: TYPE="swap" LABEL="swap" UUID="3b4dc82c-a6e6-4609-be9e-16d9206ab7fd"
/dev/sda2: UUID="72973377-c299-4ca6-ae94-2022b7dca58f" LABEL="/" TYPE="reiserfs"

And according to /proc/mounts both are mounted at the same time:

{pts/0}% cat /proc/mounts
rootfs / rootfs rw 0 0
/dev/root / reiserfs rw 0 0
/dev /dev tmpfs rw 0 0
/proc /proc proc rw 0 0
/sys /sys sysfs rw 0 0
/proc/bus/usb /proc/bus/usb usbfs rw,devgid=43,devmode=664 0 0
none /dev/pts devpts rw,mode=620 0 0
none /dev/shm tmpfs rw 0 0
none /tmp tmpfs rw 0 0
none /proc/sys/fs/binfmt_misc binfmt_misc rw 0 0
/dev/sda2 /media/hd reiserfs rw 0 0
{pts/0}% ll /dev/root
brw------- 1 root root 8, 2 2008-11-04 12:01 /dev/root
{pts/0}% ll /dev/sda2
brw-rw---- 1 root disk 8, 2 2008-11-04 12:01 /dev/sda2

Bug or feature?

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Re: 2.6.28-rc3: kernel mounts the same device twice? Or /proc/mounts lies?

[Alexey Dobriyan]

On Tue, Nov 04, 2008 at 12:13:07PM +0300, Andrey Borzenkov wrote:
> Out of some infinite wisdom something on my system decided to add
> fstab entry for "new" device after switching from IDE to PATA:
> 
> # Entry for /dev/LABEL=/ :
> LABEL=/ / reiserfs relatime,tail 1 1
> none /proc proc defaults 0 0
> none /sys sysfs defaults 0 0
> none /tmp tmpfs defaults 0 0
> # Entry for /dev/LABEL=swap :
> LABEL=swap swap swap defaults 0 0
> # Entry for /dev/sda2 :
> UUID=72973377-c299-4ca6-ae94-2022b7dca58f /media/hd reiserfs defaults 0 0
> 
> Note that both / and /media/hd refer to the same device:
> 
> {pts/0}% sudo blkid
> /dev/sda1: TYPE="swap" LABEL="swap" UUID="3b4dc82c-a6e6-4609-be9e-16d9206ab7fd"
> /dev/sda2: UUID="72973377-c299-4ca6-ae94-2022b7dca58f" LABEL="/" TYPE="reiserfs"
> 
> And according to /proc/mounts both are mounted at the same time:
> 
> {pts/0}% cat /proc/mounts
> rootfs / rootfs rw 0 0
> /dev/root / reiserfs rw 0 0
> /dev /dev tmpfs rw 0 0
> /proc /proc proc rw 0 0
> /sys /sys sysfs rw 0 0
> /proc/bus/usb /proc/bus/usb usbfs rw,devgid=43,devmode=664 0 0
> none /dev/pts devpts rw,mode=620 0 0
> none /dev/shm tmpfs rw 0 0
> none /tmp tmpfs rw 0 0
> none /proc/sys/fs/binfmt_misc binfmt_misc rw 0 0
> /dev/sda2 /media/hd reiserfs rw 0 0
> {pts/0}% ll /dev/root
> brw------- 1 root root 8, 2 2008-11-04 12:01 /dev/root
> {pts/0}% ll /dev/sda2
> brw-rw---- 1 root disk 8, 2 2008-11-04 12:01 /dev/sda2
> 
> Bug or feature?

bind mount or some userspace from LinuxOnDesktop crowd is actually mounted it second time.

Re: 2.6.28-rc3: kernel mounts the same device twice? Or /proc/mounts lies?

[Karel Zak]

On Tue, Nov 04, 2008 at 12:13:07PM +0300, Andrey Borzenkov wrote:
> And according to /proc/mounts both are mounted at the same time:
> 
> {pts/0}% cat /proc/mounts
> rootfs / rootfs rw 0 0
> /dev/root / reiserfs rw 0 0
> /dev /dev tmpfs rw 0 0
> /proc /proc proc rw 0 0
> /sys /sys sysfs rw 0 0
> /proc/bus/usb /proc/bus/usb usbfs rw,devgid=43,devmode=664 0 0
> none /dev/pts devpts rw,mode=620 0 0
> none /dev/shm tmpfs rw 0 0
> none /tmp tmpfs rw 0 0
> none /proc/sys/fs/binfmt_misc binfmt_misc rw 0 0
> /dev/sda2 /media/hd reiserfs rw 0 0
> {pts/0}% ll /dev/root
> brw------- 1 root root 8, 2 2008-11-04 12:01 /dev/root
> {pts/0}% ll /dev/sda2
> brw-rw---- 1 root disk 8, 2 2008-11-04 12:01 /dev/sda2
> 
> Bug or feature?

 Feature. This is typical FAQ-like question.

 # mount /dev/sda2 /mnt/test
 # mount /dev/sda2 /mnt/test2

 # df | grep sda2
 /dev/sda2             14877092    168740  13940448   2% /mnt/test
 /dev/sda2             14877092    168740  13940448   2% /mnt/test2

    Karel

-- 
 Karel Zak  <kzak@redhat.com>