On 5/22/18 2:45 PM, Bodo Stroesser wrote: > Patch V3. This time without 'Re: ' in Subject. > > Generally target core and TCMUser seem to work fine for tape devices and > media changers. > But there is at least one situation, where TCMUser is not able to support > sequential access device emulation correctly. > > The situation is when an initiator sends a SCSI READ CDB with a length that is > greater than the length of the tape block to read. We can distinguish two > subcases: > > A) The initiator sent the READ CDB with the SILI bit being set. > In this case the sequential access device has to transfer the data from the > tape block (only the length of the tape block) and transmit a good status. > The current interface between TCMUser and the userspace does not support > reduction of the read data size by the userspace program. > > The patch below fixes this subcase by allowing the userspace program to > specify a reduced data size in read direction. > > B) The initiator sent the READ CDB with the SILI bit not being set. > In this case the sequential access device has to transfer the data from the > tape block as in A), but additionally has to transmit CHECK CONDITION with > the ILI bit set and NO SENSE in the sensebytes. The information field in > the sensebytes must contain the residual count. > > With the below patch a user space program can specify the real read data > length and appropriate sensebytes. > TCMUser then uses the se_cmd flag SCF_TREAT_READ_AS_NORMAL, to force target > core to transmit the real data size and the sensebytes. > Note: the flag SCF_TREAT_READ_AS_NORMAL is introduced by Lee Duncan's > patch "[PATCH v4] target: transport should handle st FM/EOM/ILI reads" from > Tue, 15 May 2018 18:25:24 -0700. > > This patch was created for kernel 4.15.9. > > > Changes from RFC: > - patch now uses SCF_TREAT_READ_AS_NORMAL to fix B) also. > - comment changed accordingly > > Changes from V2: > - Cleaned up code according to review > - Userspace can set read_len for data in only, not for bidi. > - read_len from userspace no longer is checked implicitly by > gather_data_area(), but the check is done explicitly > in tcmu_handle_completion(). Now code is easier to understand. > > > Signed-off-by: Bodo Stroesser <bstroesser@xxxxxxxxxxxxxx> > > --- > include/uapi/linux/target_core_user.h | 4 ++- > drivers/target/target_core_user.c | 44 +++++++++++++++++++++++++++------- > 2 files changed, 39 insertions(+), 9 deletions(-) > > Acked-by: Bryant G. Ly <bryantly@xxxxxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe target-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
