targetcli: serialize multiple requests

[pkalever]

Problem:

targetcli/rtslib cannot handle parallel requests at the moment.
Read more about this at http://bit.ly/targetcli-parallel-requests-issue

$ for i in {1..10}; do
targetcli /backstores/fileio create ${i} /tmp/file${i} 10M& done

Created fileio 1 with size 10485760
This _Backstore already exists in configFS
This _Backstore already exists in configFS
This _Backstore already exists in configFS
This _Backstore already exists in configFS
This _Backstore already exists in configFS
Created fileio 6 with size 10485760
Created fileio 2 with size 10485760
This _Backstore already exists in configFS
Created fileio 8 with size 10485760
Created fileio 9 with size 10485760

bails-out most of the time with above errors and sometimes even crashes.

Solution:

Serialize/defend the parallel requests by simply taking a wait lock at
targetcli level, so that only one request can be processed by targetcli at
any given point in time.

Signed-off-by: Prasanna Kumar Kalever prasanna.kalever@redhat.com

[pkalever]

@maurizio-lombardi @lxbsz please help review/test.Thanks!

[lxbsz]

Tested it and worked for me.

# for i in {1..10}; do  targetcli /backstores/fileio create ${i} /tmp/file${i} 10M& done
[1] 19780
[2] 19781
[3] 19782
[4] 19783
[5] 19784
[6] 19785
[7] 19786
[8] 19787
[9] 19788
[10] 19789
# /tmp/file8 exists, using its size (10485760 bytes) instead
Created fileio 8 with size 10485760
/tmp/file3 exists, using its size (10485760 bytes) instead
Created fileio 3 with size 10485760
/tmp/file4 exists, using its size (10485760 bytes) instead
Created fileio 4 with size 10485760
/tmp/file6 exists, using its size (10485760 bytes) instead
Created fileio 6 with size 10485760
/tmp/file10 exists, using its size (10485760 bytes) instead
Created fileio 10 with size 10485760
/tmp/file1 exists, using its size (10485760 bytes) instead
Created fileio 1 with size 10485760
/tmp/file7 exists, using its size (10485760 bytes) instead
Created fileio 7 with size 10485760
/tmp/file2 exists, using its size (10485760 bytes) instead
Created fileio 2 with size 10485760
/tmp/file5 exists, using its size (10485760 bytes) instead
Created fileio 5 with size 10485760
/tmp/file9 exists, using its size (10485760 bytes) instead
Created fileio 9 with size 10485760

[1]   Done                    targetcli /backstores/fileio create ${i} /tmp/file${i} 10M
[2]   Done                    targetcli /backstores/fileio create ${i} /tmp/file${i} 10M
[3]   Done                    targetcli /backstores/fileio create ${i} /tmp/file${i} 10M
[4]   Done                    targetcli /backstores/fileio create ${i} /tmp/file${i} 10M
[5]   Done                    targetcli /backstores/fileio create ${i} /tmp/file${i} 10M
[6]   Done                    targetcli /backstores/fileio create ${i} /tmp/file${i} 10M
[7]   Done                    targetcli /backstores/fileio create ${i} /tmp/file${i} 10M
[8]   Done                    targetcli /backstores/fileio create ${i} /tmp/file${i} 10M
[9]-  Done                    targetcli /backstores/fileio create ${i} /tmp/file${i} 10M
[10]+  Done                    targetcli /backstores/fileio create ${i} /tmp/file${i} 10M

[pkalever]

@lxbsz thank you for testing it.
JFI, I have tested this with 250 devices and it works for me well locally.

[maurizio-lombardi]

Looks ok to me