[PATCH] v3 - Add exclusive locking option to block-iscsi

[Steven Haigh <netwiz@crc.id.au>]

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On 2016-05-05 15:52, Steven Haigh wrote:
> On 2016-05-05 12:32, Steven Haigh wrote:
>> Overview
>> 
>> If you're using iSCSI, you can mount a target by multiple Dom0
>> machines on the same target. For non-cluster aware filesystems, this
>> can lead to disk corruption and general bad times by all. The iSCSI
>> protocol allows the use of persistent reservations as per the SCSI
>> disk spec. Low level SCSI commands for locking are handled by the
>> sg_persist program (bundled with sg3_utils package in EL).
>> 
>> The aim of this patch is to create a 'locktarget=y' option specified
>> within the disk 'target' command for iSCSI to lock the target in
>> exclusive mode on VM start with a key generated from the local systems
>> IP, and release this lock on the shutdown of the DomU.
>> 
>> Example Config:
>> disk            =
>> ['script=block-iscsi,vdev=xvda,target=iqn=iqn.1986-03.com.sun:02:mytarget,portal=iscsi.example.com,locktarget=y']
>> 
>> In writing this, I have also re-factored parts of the script to put
>> some things in what I believe to be a better place to make expansion
>> easier. This is mainly in removing functions that purely call other
>> functions with no actual code execution.
>> 
>> Signed-off-by: Steven Haigh <netwiz@crc.id.au>
>> 
>> (on a side note, first time I've submitted a patch to the list and I'm
>> currently stuck on a webmail client, so apologies in advance if this
>> all goes wrong ;)
> 
> Changes in v2:
> Bugfix: Call find_device to locate the /dev/sdX component of the iSCSI
> target before trying to run unlock_device().
> 
> Apologies for this oversight.
> 

Changes in v3:
* Split the block-iscsi cleanup into a seperate patch 
(block-iscsi-locking-v3_01_simplify_block-iscsi.patch).
* Add locking in second patch file 
(block-iscsi-locking-v3_02_add_locking.patch)

-- 
Steven Haigh

Email: netwiz@crc.id.au
Web: https://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897

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[-- Attachment #2: block-iscsi-locking-v3_01_simplify_block-iscsi.patch --]
[-- Type: text/x-diff; name=block-iscsi-locking-v3_01_simplify_block-iscsi.patch, Size: 2910 bytes --]

--- block-iscsi.orig    2016-05-09 15:12:02.489495212 +1000
+++ block-iscsi 2016-05-09 15:16:35.447480532 +1000
@@ -31,16 +31,6 @@
     echo $1 | sed "s/^\("$2"\)//"
 }
 
-check_tools()
-{
-    if ! command -v iscsiadm > /dev/null 2>&1; then
-        fatal "Unable to find iscsiadm tool"
-    fi
-    if [ "$multipath" = "y" ] && ! command -v multipath > /dev/null 2>&1; then
-        fatal "Unable to find multipath"
-    fi
-}
-
 # Sets the following global variables based on the params field passed in as
 # a parameter: iqn, portal, auth_method, user, multipath, password
 parse_target()
@@ -52,12 +42,18 @@
         case $param in
         iqn=*)
             iqn=$(remove_label $param "iqn=")
+            if ! command -v iscsiadm > /dev/null 2>&1; then
+                fatal "Could not find iscsiadm tool."
+            fi
             ;;
         portal=*)
             portal=$(remove_label $param "portal=")
             ;;
         multipath=*)
             multipath=$(remove_label $param "multipath=")
+            if ! command -v multipath > /dev/null 2>&1; then
+                fatal "Multipath selected, but no multipath tools found"
+            fi
             ;;
         esac
     done
@@ -96,40 +92,6 @@
     fi
 }

-# Attaches the target $iqn in $portal and sets $dev to point to the
-# multipath device
-attach()
-{
-    do_or_die iscsiadm -m node --targetname "$iqn" -p "$portal" --login > /dev/null
-    find_device
-}
-
-# Discovers targets in $portal and checks that $iqn is one of those targets
-# Also sets the auth parameters to attach the device
-prepare()
-{
-    # Check if target is already opened
-    iscsiadm -m session 2>&1 | grep -q "$iqn" && fatal "Device already opened"
-    # Discover portal targets
-    iscsiadm -m discovery -t st -p $portal 2>&1 | grep -q "$iqn" || \
-        fatal "No matching target iqn found"
-}
-
-# Attaches the device and writes xenstore backend entries to connect
-# the device
-add()
-{
-    attach
-    write_dev $dev
-}
-
-# Disconnects the device
-remove()
-{
-    find_device
-    do_or_die iscsiadm -m node --targetname "$iqn" -p "$portal" --logout > /dev/null
-}
-
 command=$1
 target=$(xenstore-read $XENBUS_PATH/params || true)
 if [ -z "$target" ]; then
@@ -138,15 +100,21 @@

 parse_target "$target"

-check_tools || exit 1
-
 case $command in
 add)
-    prepare
-    add
+    # Check if target is already opened
+    iscsiadm -m session 2>&1 | grep -q "$iqn" && fatal "Device already opened"
+    # Discover portal targets
+    iscsiadm -m discovery -t st -p $portal 2>&1 | grep -q "$iqn" || \
+        fatal "No matching target iqn found"
+
+    ## Login to the iSCSI target.
+    do_or_die iscsiadm -m node --targetname "$iqn" -p "$portal" --login > /dev/null
+
+    write_dev $dev
     ;;
 remove)
-    remove
+    do_or_die iscsiadm -m node --targetname "$iqn" -p "$portal" --logout > /dev/null
     ;;
 *)
     exit 1 

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[-- Attachment #3: block-iscsi-locking-v3_02_add_locking.patch --]
[-- Type: text/x-diff; name=block-iscsi-locking-v3_02_add_locking.patch, Size: 2382 bytes --]

--- block-iscsi 2016-05-09 15:16:35.447480532 +1000
+++ block-iscsi-lock    2016-05-05 15:43:58.222159351 +1000
@@ -37,8 +37,7 @@
 {
     # set multipath default value
     multipath="n"
-    for param in $(echo "$1" | tr "," "\n")
-    do
+    for param in $(echo "$1" | tr "," "\n"); do
         case $param in
         iqn=*)
             iqn=$(remove_label $param "iqn=")
@@ -55,6 +54,15 @@
                 fatal "Multipath selected, but no multipath tools found"
             fi
             ;;
+        locktarget=*)
+            locktarget=$(remove_label $param "locktarget=")
+            if ! command -v sg_persist > /dev/null 2>&1; then
+                fatal "Locking requested but no sg_persist found"
+            fi
+            if ! command -v gethostip > /dev/null 2>&1; then
+                fatal "Locking requested but no gethostip found for key generation"
+            fi
+            ;;
         esac
     done
     if [ -z "$iqn" ] || [ -z "$portal" ]; then
@@ -92,6 +100,31 @@
     fi
 }

+
+lock_device()
+{
+    ## Lock the iSCSI target as Exclusive Access.
+    key=$(gethostip -x $(uname -n))
+    if ! sg_persist -d ${dev} -o -G -S ${key} > /dev/null; then
+        unlock_device
+        iscsiadm -m node --targetname "$iqn" -p "$portal" --logout > /dev/null
+        fatal "iSCSI LOCK: Failed to register with target"
+    fi
+    if ! sg_persist -d ${dev} -o -R -K ${key} -T 6 > /dev/null; then
+        unlock_device
+        iscsiadm -m node --targetname "$iqn" -p "$portal" --logout > /dev/null
+        fatal "iSCSI LOCK: Failed to set persistent reservation"
+    fi
+}
+
+unlock_device()
+{
+    ## Unlock the iSCSI target.
+    key=$(gethostip -x $(uname -n))
+    sg_persist -d ${dev} -o -L -K ${key} -T 6 > /dev/null || true
+    sg_persist -d ${dev} -o -G -K ${key} -S 0 > /dev/null || true
+}
+
 command=$1
 target=$(xenstore-read $XENBUS_PATH/params || true)
 if [ -z "$target" ]; then
@@ -110,10 +143,17 @@

     ## Login to the iSCSI target.
     do_or_die iscsiadm -m node --targetname "$iqn" -p "$portal" --login > /dev/null
-
+    find_device
+    if [ "$locktarget" = "y" ]; then
+        lock_device
+    fi
     write_dev $dev
     ;;
 remove)
+    find_device
+    if [ "$locktarget" = "y" ]; then
+        unlock_device
+    fi
     do_or_die iscsiadm -m node --targetname "$iqn" -p "$portal" --logout > /dev/null
     ;;
 *) 

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