Messages in this thread | | | Date | Fri, 08 Feb 2008 17:42:50 +0300 | From | Vladislav Bolkhovitin <> | Subject | Re: Integration of SCST in the mainstream Linux kernel |
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Nicholas A. Bellinger wrote: > On Thu, 2008-02-07 at 12:37 -0800, Luben Tuikov wrote: > >>Is there an open iSCSI Target implementation which does NOT >>issue commands to sub-target devices via the SCSI mid-layer, but >>bypasses it completely? >> >> Luben >> > > > Hi Luben, > > I am guessing you mean futher down the stack, which I don't know this to > be the case. Going futher up the layers is the design of v2.9 LIO-SE. > There is a diagram explaining the basic concepts from a 10,000 foot > level. > > http://linux-iscsi.org/builds/user/nab/storage-engine-concept.pdf > > Note that only traditional iSCSI target is currently implemented in v2.9 > LIO-SE codebase in the list of target mode fabrics on left side of the > layout. The API between the protocol headers that does > encoding/decoding target mode storage packets is probably the least > mature area of the LIO stack (because it has always been iSCSI looking > towards iSER :). I don't know who has the most mature API between the > storage engine and target storage protocol for doing this between SCST > and STGT, I am guessing SCST because of the difference in age of the > projects. Could someone be so kind to fill me in on this..?
SCST uses scsi_execute_async_fifo() function to submit commands to SCSI devices in the pass-through mode. This function is slightly modified version of scsi_execute_async(), which submits requests in FIFO order instead of LIFO as scsi_execute_async() does (so with scsi_execute_async() they are executed in the reverse order). Scsi_execute_async_fifo() added as a separate patch to the kernel.
> Also note, the storage engine plugin for doing userspace passthrough on > the right is also currently not implemented. Userspace passthrough in > this context is an target engine I/O that is enforcing max_sector and > sector_size limitiations, and encodes/decodes target storage protocol > packets all out of view of userspace. The addressing will be completely > different if we are pointing SE target packets at non SCSI target ports > in userspace. > > --nab
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