On Wed, 2008-07-02 at 15:20 +0200, Arne Wiebalck wrote: > Hi all, > > I am trying to replace some read/write calls in our application > by SG_IO commands in order to have access to the sense bytes in > case of an error. The underlying devices are tape drives. > > Part of our application, such as positioning or reading labels > from the tape, are run as root. This seems to work fine, I get > the data I expect and the sense bytes in case of an error. > > However, the actual data transfer from and to the device is run > under a user's ID. This part does not work anymore when switching > from read/write to SG_IO: 'Operation not permitted'. > > Does a user need some special rights to issue SG_IO (read) commands > (on a file descriptor that he opened for reading and that he > can use without problems for read() calls)? > > The device node that the processes are accessing is a char special > file owned by the user and with all user bits set. This special file > is created on a per tape request basis. I also tried to use /dev/nst0 > instead, but that made no difference. > > I am running a relatively old kernel (2.6.9 based), could that cause > any problem? > > BTW, why does it say "except st" on the permission requirements table on > http://sg.torque.net/sg/sg_io.html ? :) > > > Any hints appreciated. SG_IO access requires CAP_SYS_RAWIO to defeat the command verifier. James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
