thanks...yes, it helped :-) On Sunday, January 12, 2020 at 4:32:55 AM UTC+1, The Lee-Man wrote: > > On Jan 11, 2020, at 11:26 AM, Bobby <italien...@gmail.com <javascript:>> > wrote: > > > Hi , > > Thanks for your patience regarding my questions. Because after I had dug > (digged) very older posts, I realized > many of the older posts already had answers for many of my earlier > questions :). After your couple of answers and going > through old posts, I have a better understanding of *user land* and *kernel > land*. > > > Excellent. > > > Now one more point. > > *Kernel land: * > While we are at kernel land, I have a confusion on that. > AFAIK in linux kernel, the linux *block layer* is a glue that, on the one > hand, allows applications to access > diverse storage devices > in a uniform way, and on the other hand, > provides storage devices and drivers with a single point of entry from all > applications. > I mean this Linux OS (host) block layer is the most > critical part of the I/O hierarchy, as it orchestrates the I/O > requests from different applications to the underlying storage. > > *Question:* > So in context of *Open-iSCSI*, where does the user-land interacts the > block layer in the kernel land? I > mean, when it comes to kernel land, why we are considering only > *scsi_transport_iscsi.c* and *iscsi_tcp.c* codes? Shouldn't > the block request go through block layer? > > As always, thanks in advance :) > > > > The iscsi initiator (open-iscsi) acts as an HBA, in effect, in the block > system. > > The layer above the block layer (conceptually) are the disc or tape > drivers.The block layer presents an abstract interface to them, so that > they only have to deal with putting bits in blocks, or getting bits from > blocks. > > The layer below the block layer, on the other hand, gets requests to put > bits in blocks or to get bits from blocks, and has to deal with how to > actually implement that, given where the bits live. For a local disc, this > is an HBA adapter driver. For iSCSI, this is actually a transport rather > than an HBA. There are several transports, for example iSER (Infiniband) is > another. > > I hope that helps. > — > Lee > > >
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