https://bugzilla.kernel.org/show_bug.cgi?id=191381
Bug ID: 191381
Summary: LIO ignores XCOPY source and destination descriptor
IDs
Product: IO/Storage
Version: 2.5
Kernel Version: 4.9.0
Hardware: All
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: SCSI
Assignee: [email protected]
Reporter: [email protected]
Regression: No
The EXTENDED COPY SCSI command (XCOPY) is used extensively by VMware ESX
initiators, to offload to the iSCSI target, the process of copying data between
a source and destination LU region.
XCOPY is also supported by other initiators, such as ddpt
(http://sg.danny.cz/sg/ddpt.html), libiscsi, etc.
The XCOPY specification in SPC-4 (revision 37) states that the XCOPY source and
destination device(s) should be derived from the copy source and copy
destination descriptor (CSCD) IDs in the XCOPY segment descriptor. The CSCD IDs
are generally (for block -> block copies), indexes into the corresponding CSCD
list, i.e.
=================================
XCOPY Header
=================================
CSCD List
- entry 0
+ LU ID
- entry 2
+ LU ID
=================================
Segment Descriptor List
- segment 0
+ src CSCD ID = (CSCD entry 0)
+ dest CSCD ID = (CSCD entry 1)
+ len
+ src lba
+ dest lba
=================================
Currently LIO completely ignores the src and dest CSCD IDs in the Segment
Descriptor List, and instead assumes that the first entry in the CSCD list
corresponds to the source, and the second to the destination.
This assumption appears to stand true for XCOPY requests from ESXi initiators.
However, deviation from the spec may break other initiators - it causes a
number of libiscsi tests to fail.
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