Updated documentation README.md in iscsi branch.

2 files changed, 112 insertions, 4 deletions

diff --git a/README.md b/README.md
index a77a64d..0220f63 100644
--- a/README.md
+++ b/README.md
@@ -490,11 +490,25 @@ The _iscsi.conf_ file is the main configuration file for the iSCSI implementatio
 
 [iscsi]
 ; Target name check level (warning) specifying invalid check levels will default to full
-; validation!). Default is Full
+; validation!). Default is Relaxed
 ; Full      Target name is checked for full standaard compliance (recommended)
 ; Relaxed   All invalid characters according to standard will be allowed if not an IQN, NAA or EUI.
 ; None      No checking at all (be careful)
-TargetNameCheck=Full
+TargetNameCheck=Relaxed
+
+...
+
+; Login/Text Operational Session Text Key: Maximum receive DataSegmentLength.
+;
+* The initiator or target declares the maximum data segment length in bytes it can receive in an
+; iSCSI PDU.
+* The transmitter (initiator or target) is required to send PDUs with a data segment that does not
+; exceed MaxRecvDataSegmentLength of the receiver. A target receiver is additionally limited by
+; MaxBurstLength for solicited data and FirstBurstLength for unsolicited dataAn initiator MUST NOT
+; send solicited PDUs exceeding MaxBurstLength nor unsolicited PDUs exceeding FirstBurstLength (or
+; FirstBurstLength-Immediate Data Length if immediate data were sent). Valid values range from 512
+; to 16777215 bytes. Default is 65536 bytes (64 KiB)
+MaxRecvDataSegmentLength=65536
 
 ...
 
@@ -575,6 +589,100 @@ PhysicalReadOnly=true
 For a complete list of possible configuration options, look at the comments in the sample _iscsi.conf_ file, which describes the options in detail.
 
 
-### _World Wide Name (WWN)_ to DNBD3 image mapping for standard compliance.
+### _World Wide Name (WWN)_ to DNBD3 image mapping for standard compliance
 As the iSCSI target node name supports only a very restricted number of allowed characters, DNBD3 images also can be specified either using the _Network Address Authority (NAA) IEEE Extended_ name identifier, the _64-bit extended unique identifier (EUI-64)_ or _iSCSI Qualified Name (IQN)_ using the _wwn-0x_ prefix. The revision of the DNBD3 image is specified with a _:_ (colon) after the DNBD3 image name and also the _Logical Unit Number (LUN)_.
 
+This naming scheme is required when _TargetNameCheck_ is either set to _Full_ or when using other initiators which require standard compliance _IQN_ naming schemes.
+
+The image information with their _WWN_ can be retrieved as _JSON_ for all images using the URL:
+
+```
+http://<iscsi-server>:<port>/query?q=images
+```
+
+Note that the _WWN_ is in decimal integer _JSON_ format. The target node name expects the _WWN_ to be passed as hexadecimal.
+
+
+### Using _iscsiadm_ to attach and detach DNBD3 images as block device as a replacement for the _DNBD3_ kernel and _FUSE_ module.
+You can use _iscsiadm_, which on Debian und Ubuntu based distributions can be found in the package _open-iscsi_:
+
+```shell
+apt-get install open-iscsi
+```
+
+After successful installation, it is possible to attach _iSCSI_ devices as regular block devices like _/dev/sda_.
+Since _iSCSI_ discovery is **NOT** supported yet, target nodes have to be created manually:
+
+```shell
+iscsiadm -m node -T <image-name> -p <iscsi-server>:<port> --op=new
+```
+
+This will create an _iSCSI_ target node _image-name_ which is attached to the portal _iscsi-server_ listening on port _port_.
+A target node configuration file will be created in _/etc/iscsi/nodes/<image-name>/<iscsi-server>,<port>_.
+Please note that for any images residing in sub directories of the base path, the sub directory tree has to be created manually in _/etc/iscsi/nodes_ and _/etc/iscsi/static_ before adding the target node with _iscsiadm_.
+
+After the target node has been created, it can be made available as a block device using:
+
+```shell
+iscsiadm -m node -T <image-name> -p <iscsi-server>:<port> --login
+```
+
+Now the image is accessible using either e.g. _/dev/sda_ or _/dev/disk/by-id_.
+If the operating system has removable device attach mechanisms, they will be invoked, too.
+
+After finishing work with the image, the _iSCSI_ session needs to be logged out with:
+
+```shell
+iscsiadm -m node -T <image-name> -p <iscsi-server>:<port> --logout
+```
+
+Now the block device e.g. _/dev/sda_ and links in _/dev/disk/by-id_ will be removed.
+If the operating system has removable device detach mechanisms, they will be invoked, too.
+
+If the _iSCSI_ target node is not required anymore, it can be removed using:
+
+```shell
+iscsiadm -m node -T <image-name> -p <iscsi-server>:<port> --op=delete
+```
+
+This will delete the target node in _/etc/iscsi/nodes/<image-name>/<iscsi-server>,<port>_ and also remove the directory _/etc/iscsi/nodes/<image-name>_ if empty.
+Please note that for any images residing in sub directories of the base path, the sub directory tree has to be removed manually from _/etc/iscsi/nodes_ and _/etc/iscsi/static_ after removing the target node with _iscsiadm_.
+
+
+### Configuring and using _QEMU_ for using the iSCSI server
+Here is a bash script called _qemu-iscsi.sh_ that invokes QEMU with iSCSI.
+
+```shell
+#!/bin/bash
+
+CRC32C='None'
+
+[ -n "$3" ] && CRC32C="$3"
+
+qemu-system-x86_64 \
+  -enable-kvm \
+  -m 4096 \
+  -smp 4 \
+  -cpu host \
+  -machine type=q35,accel=kvm \
+  -boot menu=on \
+  -device virtio-scsi-pci,id=scsi0 \
+  -drive if=none,file=/data/storage/ubuntu.2404.lts.img.r1,format=raw,id=drive0,cache=none \
+  -device scsi-hd,drive=drive0,bus=scsi0.0 \
+  -drive if=none,id=iscsi0,file=iscsi://localhost:5003/iqn.2025-07.de.uni-freiburg.rz:dnbd3:images:"$1":"$2"/"$2",format=raw,cache=none,aio=native,readonly=on \
+  -device scsi-hd,drive=iscsi0,bus=scsi0.0 \
+  -iscsi initiator-name=iqn.2025-07.de.uni-freiburg.rz:bwlehrpool:client:"$(hostname)":"$1":"$2" \
+  -iscsi header-digest="${CRC32C}" \
+  -display gtk
+```
+
+Usage:
+
+```shell
+qemu-iscsi.sh <image-name> <image-revision> [CRC32C]
+```
+
+This will invoke QEMU with a KVM accelerated virtual machine with 4 GiB memory and 4 CPU cores, a primary writable local hard drive located in _/data/storage/ubuntu.2404.lts.img.r1_ and a secondary read only _DNBD3_ <image-name> with revision <image-revision> attached via iSCSI protocol on _localhost_ using port _5003_.
+The QEMU client will get the initiator name _iqn.2025-07.de.uni-freiburg.rz:bwlehrpool:client:<your-hostname>:<image-name>:<image-revision>_.
+If the third optional argument _CRC32C_ is passed, iSCSI header CRC32C checksumming will be enabled.
+
diff --git a/src/server/iscsi.c b/src/server/iscsi.c
index 2ca2225..4c0fc4d 100644
--- a/src/server/iscsi.c
+++ b/src/server/iscsi.c
@@ -1311,7 +1311,7 @@ int iscsi_create()
 			return -1;
 		}
 
-		globvec->flags                          = (ISCSI_GLOBALS_FLAGS_INIT_R2T | ISCSI_GLOBALS_FLAGS_IMMEDIATE_DATA | ISCSI_GLOBALS_FLAGS_DATA_PDU_IN_ORDER | ISCSI_GLOBALS_FLAGS_DATA_SEQ_IN_ORDER | ISCSI_GLOBALS_FLAGS_SCSI_IO_REMOVABLE | ISCSI_GLOBALS_FLAGS_SCSI_IO_WRITE_PROTECT);
+		globvec->flags                          = (ISCSI_GLOBALS_FLAGS_CHAP_DISABLE | ISCSI_GLOBALS_FLAGS_INIT_R2T | ISCSI_GLOBALS_FLAGS_IMMEDIATE_DATA | ISCSI_GLOBALS_FLAGS_DATA_PDU_IN_ORDER | ISCSI_GLOBALS_FLAGS_DATA_SEQ_IN_ORDER | ISCSI_GLOBALS_FLAGS_SCSI_IO_REMOVABLE | ISCSI_GLOBALS_FLAGS_SCSI_IO_WRITE_PROTECT);
 		globvec->target_name_check              = ISCSI_GLOBALS_TARGET_NAME_CHECK_RELAXED;
 		globvec->max_sessions                   = 0U;
 		globvec->header_digest                  = 0;