At Tue, 5 Aug 2014 13:53:49 +0900, Hitoshi Mitake wrote: > > This patchset implements iSCSI multipath support in sheepdog. Below is > a brief description of the problem and solution (mainly quoting from > 2nd patch): > > The main problem of enabling iSCSI multipath for sheepdog's VDI is > keeping coherence of tgtd's internal inode data structure. Assume tgt > A and B have logical units which point same sheepdog VDI. After > initialization of the logical units, A and B have copies of inode > object in their address space (let's X denote this object). When an > initiator sends write request to A and the request causes COW, A > creates a new object and updates the inode object X (let's X' denote > the updated one). > > After the update by A, A can die with hardware faults. In such a case, > the initiator detects a connection error and switch its target to B if > iSCSI multipath is configured correctly. But the problem can arise at > this point. Because B doesn't know the update caused by A and its > internal inode object is still X, not X'. B creates requests based on > X, so it can read obsolete data which is already hidden by X' or > update X' in wrong manner. > > For solving the above problem, this patchset implements a mechanism > for keeping inode objects consistent in clients' address spaces. The > above problem is very similar to cache coherence problem of shared > memory multicore processors, so the mechanism mocks a simple MSI > protocol. When VDI is locked with shared mode for iSCSI multipath, > sheep's internal data structure for representing locking has 3 states > (Modified, Shared, and Invalidated) per participating node (in the > above example, A and B). > > The above states are updated via gateway read and write of inode > objects: read makes states of every node shared, write makes writer's > state modified and others invalidated. > > With the above protocol, sheepdog can prevent requests from tgt based > on obsolete inode object. > > Corresponding changes for QEMU and tgt can be found: > - QEMU: https://github.com/sheepdog/qemu/tree/iscsi-multipath > -- change for QEMU is just for adopting protocol update > - tgt: https://github.com/sheepdog/tgt/tree/iscsi-multipath > > Hitoshi Mitake (4): > sheepdog proto: a new field type in vdi request for locking > sheep, dog: introduce a new state for expressing coherence of inode > objects in clients > sheep: implement coherence protocol of inode objects in address spaces > of clients > sheep: handle node leave event for updating inode object shared state > > dog/vdi.c | 32 ++- > include/internal_proto.h | 28 ++- > include/sheepdog_proto.h | 10 + > sheep/gateway.c | 24 ++- > sheep/group.c | 2 + > sheep/ops.c | 33 ++- > sheep/sheep_priv.h | 14 +- > sheep/vdi.c | 518 > ++++++++++++++++++++++++++++++++++++++++++----- > 8 files changed, 588 insertions(+), 73 deletions(-)
Applied this series because nobody disagrees with it. Thanks, Hitoshi -- sheepdog mailing list sheepdog@lists.wpkg.org http://lists.wpkg.org/mailman/listinfo/sheepdog
