Like above, can you please give me more hints/clues in which other code(s) I need to see. Which part of this gigantic MQ-Block layer code base to see to understand the complete data flow? I am particularly interested in Hash , Map data structures.
On Tuesday, December 10, 2019 at 11:34:49 AM UTC+1, Bobby wrote: > > > Perfect ! After this reply, I had to dig deeper and now it makes > sense....thanks a lot The Lee-Man for explaining it so effectively... > > > On Saturday, November 9, 2019 at 7:52:52 PM UTC+1, The Lee-Man wrote: >> >> On Friday, November 8, 2019 at 10:40:08 AM UTC-8, Bobby wrote: >>> >>> >>> Hi Ulrich, >>> >>> Thanks for the hint. Can you please help me regarding following two >>> questions. >>> >>> - Linux block layer perform IO scheduling IO submissions to storage >>> device driver. If there is a physical device, the block layer interacts >>> with it through SCSI mid layer and SCSI low level drivers. So, how >>> *actually* a software initiator (*Open-iSCSI*) interacts with "*block >>> layer*"? >>> >>> - What confuses me, where does the "*disk driver*" comes into play? >>> >>> Thanks :-) >>> >>> >> In an iSCSI connection (session), there is the initiator and the target. >> I assume you are talking about the initiator. >> >> On the initiator, the "magic" is done by the kernel, in particular the >> iSCSI initiator code in the kernel, specifically by the >> scsi_transport_iscsi.c in drivers/scsi. When an iSCSI connection is made, >> the code creates a new "host" object, and then tests the device at the >> other end of the connection. If it's a disc drive, then an instance of sd >> is created (the disc driver). If the device is tape, a tape driver is >> instantiated (st). Unrecognized devices still get a generic SCSI device >> node, I believe. >> >> So, in this way, iSCSI is acting like an adapter driver, which plugs into >> the SCSI mid-layer. >> >> You can run "sudo journalctl -xe --follow" in one window, then log into >> an existing target in another (I used "sudo iscsiadm -m node -l"), and you >> should see this kind of output from journalctl: >> >> ... >> >> >> >>> Nov 09 10:46:59 linux-dell kernel: iscsi: registered transport (tcp) >>> Nov 09 10:46:59 linux-dell kernel: scsi host3: iSCSI Initiator over >>> TCP/IP >>> Nov 09 10:46:59 linux-dell iscsid[13175]: iscsid: Connection1:0 to >>> [target: iqn.2003-01.org.linux-iscsi.linux-dell.x8664:sn.2a6e21b1b53c, >>> portal: 192.168.20.3,3260] through [iface: default] is operational now >>> Nov 09 10:46:59 linux-dell kernel: scsi 3:0:0:0: Direct-Access >>> LIO-ORG test-disc 4.0 PQ: 0 ANSI: 5 >>> Nov 09 10:46:59 linux-dell kernel: scsi 3:0:0:0: alua: supports implicit >>> and explicit TPGS >>> Nov 09 10:46:59 linux-dell kernel: scsi 3:0:0:0: alua: device >>> naa.6001405de01c6e7933b414e901e22b0f port group 0 rel port 1 >>> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: Attached scsi generic sg1 >>> type 0 >>> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] 2097152 512-byte >>> logical blocks: (1.07 GB/1.00 GiB) >>> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] Write Protect is off >>> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] Mode Sense: 43 00 >>> 10 08 >>> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] Write cache: >>> enabled, read cache: enabled, supports DPO and FUA >>> Nov 09 10:46:59 linux-dell kernel: >>> iSCSI/iqn.1996-04.de.suse:01:54cab487975b: Unsupported SCSI Opcode 0xa3, >>> sending CHECK_CONDITION. >>> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] Optimal transfer >>> size 8388608 bytes >>> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: [sdb] Attached SCSI disk >>> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: alua: transition timeout >>> set to 60 seconds >>> Nov 09 10:46:59 linux-dell kernel: sd 3:0:0:0: alua: port group 00 state >>> A non-preferred supports TOlUSNA >>> >> ... >> >> -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/open-iscsi/66d69bcc-1650-4df8-86dc-ad631d4da5c4%40googlegroups.com.
