On Wednesday 29 Dec 2010 10:31:37 pm Greg Freemyer wrote: > On Wed, Dec 29, 2010 at 11:12 AM, Mulyadi Santosa > > <mulyadi.santosa@xxxxxxxxx> wrote: > > On Wed, Dec 29, 2010 at 20:06, Prasad Joshi <prasadjoshi124@xxxxxxxxx> wrote: > >> Hello All, > >> > >> ZFS file system has a property called devices. If turned off, ZFS > >> would not allow access to the device files (block/character) present > >> on the file system. I want to implement the same behavior on the a > >> Linux File System. > > > > I don't know about ZFS, so could you please elaborate on what you mean > > by "ZFS could disallow access"? > > > > IMHO, (untested), you could simply do it using usual Linux > > file/directory permission up to SELinux/AppArmor....so, is that what > > you mean? > > > > -- > > regards, > > > > Mulyadi Santosa > > Mulyadi, > > My guess is that it is more complex than that. > > Some filesystems have issues if the raw drive is read while the > filesystem is mounted. I think it is caused by inconsistencies in the > various cache's. ie. iirc, At least in the 2.4 kernel there was not a > single unified cache for block layer and filesystems. So doing raw > reads of underlying device while it was mounted could cause the caches > to get out of sync. > > I don't recall the details, but either the kernel would oops or the > filesystem would become corrupt. I don't know if any 2.6 filesystems > still have that issue. Anyway ZFS must have a similar issue. > > So a ZFS filesystem developer knowing this was a conflict could add a > check in the /dev/sda open() that would fail the open if there was a > mounted filesystem of type ZFS on the drive. > > And the mount should fail if /dev/sda is already open. > > I'm not aware of the 2.6.x linux kernel offering any infrastructure to > help with that issue. > > Greg > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies@xxxxxxxxxxxxxxxxx > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies Greg, > So doing raw > reads of underlying device while it was mounted could cause the caches > to get out of sync. So doing a 'dd' would cause the kernel to oops? Thanks. _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
