openssh unix dev - Jan 2013 - sftp does not allow rename across file system

Hello:
I got the error
EXDEV (Invalid cross-device link)
when renaming one file to another directory that is actually mounting 
another file system.

I am using SSH-2.0-OpenSSH_6

with standard SFTP setup as below

Subsystem       sftp    internal-sftp

Match group sftponly
         ChrootDirectory /home/sftp/%u
         X11Forwarding no
         AllowTcpForwarding no
         ForceCommand internal-sftp

there are two subdirs in a user home
subPlain  (a plain unix dir)
subMounted  (a dir that is actually mounting a different file system, or 
using mount --bind <targetDir> subMounted  )

when using sftp rename

rename subPlaib/F1 subPlaib/F2
works fine.
but

rename subPlaib/F1 subMounted/F2

failed

strace output shows the error as

read(0, "\0\0\0H\310\0\0\0&\0\0\0\30posix-rename at openss"...,
16384) = 76
rename("/johnson/ttt", "/johnson/shared/kkk") = -1 EXDEV
(Invalid
cross-device link)
select(2, [0], [1], NULL, NULL)         = 1 (out [1])
write(1, "\0\0\0\30e\0\0\0&\0\0\0\4\0\0\0\7Failure\0\0\0\0", 28) =
28

I have tried with different sftp clients without success.

Any help would be appreciated.

Thanks

-Ted

On Thu, 17 Jan 2013, Ted Smith wrote:
> Hello:
> I got the error
> EXDEV (Invalid cross-device link)
> when renaming one file to another directory that is actually mounting
another
> file system.
This is expected behaviour at the moment. The sftp protocol doesn't have
a mechanism to do cross-device rename (a misnomer, since it isn't renaming
but copying).

Fixing this will require a protocol extension. It isn't hard, but someone
needs to do the work.

-d