1

I setup a block level device-mapper target, and when I am writing to it using the following dd command:

dd if=/dev/zero of=/dev/mapper/mytarget bs=4096 count=5

I have observed that there are a lot of read requests (i.e., bios with read direction). I am unable comprehend what is going on.

As far as I understood, the above dd command should write to my device-mapper target. But why it is reading from it? Is it because I am reading from /dev/zero? But that should not be a part of device-mapper, right? What am I missing here?

For more information, I am using this device-mapper-target. It is a dm target for block-level deduplication. This is the specific source code file. I inserted some debug messages using DMINFO(). I later used dmesg to see the outputs.

If the count=5 in dd command, there is 1 write request and 5 read requests.

output from dmesg command:

[ 6167.008310] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.008325] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.008328] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.008331] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.008334] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.008379] device-mapper: dedup-mod: Entered do_work() function
[ 6167.008380] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.008381] device-mapper: dedup-mod: Entered handle_write() function
[ 6167.008405] device-mapper: dedup-mod: 

[ 6167.008407] device-mapper: dedup-mod: Entered do_io (others) with lbn: 0 and pbn: 0
[ 6167.008408] device-mapper: dedup-mod: 

[ 6167.008451] device-mapper: dedup-mod: Entered do_work() function
[ 6167.008452] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.008453] device-mapper: dedup-mod: Entered handle_write() function
[ 6167.008492] device-mapper: dedup-mod: Entered do_work() function
[ 6167.008493] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.008494] device-mapper: dedup-mod: Entered handle_write() function
[ 6167.008515] device-mapper: dedup-mod: Entered do_work() function
[ 6167.008516] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.008517] device-mapper: dedup-mod: Entered handle_write() function
[ 6167.008539] device-mapper: dedup-mod: Entered do_work() function
[ 6167.008539] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.008540] device-mapper: dedup-mod: Entered handle_write() function
[ 6167.010254] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010335] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010337] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010338] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010382] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010403] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010404] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010404] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010420] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010429] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010456] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010457] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010459] device-mapper: dedup-mod: 

[ 6167.010460] device-mapper: dedup-mod: Entered do_io_read with lbn: 0 and pbn: 0
[ 6167.010461] device-mapper: dedup-mod: 

[ 6167.010517] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010536] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010537] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010538] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010539] device-mapper: dedup-mod: 

[ 6167.010540] device-mapper: dedup-mod: Entered do_io_read with lbn: 1 and pbn: 0
[ 6167.010541] device-mapper: dedup-mod: 

[ 6167.010598] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010621] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010622] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010623] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010649] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010658] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010659] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010661] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010685] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010693] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010695] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010695] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010712] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010720] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010721] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010722] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010738] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010747] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010748] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010748] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010762] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010770] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010771] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010773] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010786] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010794] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010795] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010796] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010809] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010817] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010818] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010819] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010838] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010846] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010847] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010848] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010862] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010870] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010871] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010872] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010886] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010888] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010890] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010890] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010906] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010915] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010916] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010924] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010938] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010946] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010947] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010948] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.010976] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.010985] device-mapper: dedup-mod: Entered do_work() function
[ 6167.010986] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.010987] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011008] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011016] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011017] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011018] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011019] device-mapper: dedup-mod: 

[ 6167.011020] device-mapper: dedup-mod: Entered do_io_read with lbn: 3 and pbn: 0
[ 6167.011022] device-mapper: dedup-mod: 

[ 6167.011047] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011056] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011057] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011057] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011072] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011081] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011082] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011083] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011528] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011542] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011543] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011545] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011551] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011553] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011554] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011556] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011557] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011558] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011560] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011569] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011570] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011572] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011573] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011574] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011575] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011577] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011578] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011579] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011581] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011583] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011585] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011586] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011587] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011589] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011590] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011592] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011593] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011596] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011598] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011614] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011616] device-mapper: dedup-mod: 

[ 6167.011618] device-mapper: dedup-mod: Entered do_io_read with lbn: 2 and pbn: 0
[ 6167.011619] device-mapper: dedup-mod: 

[ 6167.011634] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011635] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011635] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011636] device-mapper: dedup-mod: 

[ 6167.011637] device-mapper: dedup-mod: Entered do_io_read with lbn: 4 and pbn: 0
[ 6167.011638] device-mapper: dedup-mod: 

[ 6167.011641] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011641] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011642] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011645] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011646] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011647] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011652] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011653] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011654] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011656] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011657] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011659] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011661] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011662] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011663] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011665] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011666] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011667] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011669] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011670] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011671] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011673] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011674] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011675] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011677] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011679] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011679] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011689] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011690] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011690] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011693] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011694] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011695] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011698] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011699] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011699] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011702] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011703] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011703] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011706] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011706] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011707] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011710] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011710] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011711] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011713] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011714] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011715] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011717] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011718] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011730] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011733] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011734] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011735] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011737] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011738] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011738] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011741] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011742] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011742] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011745] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011746] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011747] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011749] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011750] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011751] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011753] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011754] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011754] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011757] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011758] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011759] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011761] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011762] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011763] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011766] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011767] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011768] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011770] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011771] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011772] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011838] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011848] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011849] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011851] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011852] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011854] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011856] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011858] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011859] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011860] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011865] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011866] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011867] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011868] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011869] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011872] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011873] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011874] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011876] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011878] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011879] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011881] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011883] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011884] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011885] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011886] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011897] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011899] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011900] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011906] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011907] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011909] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011910] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011911] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011912] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011915] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011916] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011916] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011918] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011920] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011921] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011923] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011924] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011925] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011927] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011928] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011928] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011930] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011933] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011934] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011935] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011936] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011937] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011941] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011942] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011944] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011945] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011947] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011948] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011948] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011951] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011952] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011953] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011954] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011955] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011957] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011959] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011960] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011961] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011963] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011964] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011965] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011966] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011970] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011971] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011973] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011974] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011976] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011978] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011978] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.011980] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.011981] device-mapper: dedup-mod: Entered do_work() function
[ 6167.011997] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.011999] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012002] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012003] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012004] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012006] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012007] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012008] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012010] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012011] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012012] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012014] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012015] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012015] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012025] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012025] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012026] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012028] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012029] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012030] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012039] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012041] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012042] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012051] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012052] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012052] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012060] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012061] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012062] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012064] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012066] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012067] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012070] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012071] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012072] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012074] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012075] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012076] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012151] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.012166] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012166] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012167] device-mapper: dedup-mod: Entered handle_read() function
[ 6167.012193] device-mapper: dedup-mod: Entered dedup_defer_bio() function
[ 6167.012261] device-mapper: dedup-mod: Entered do_work() function
[ 6167.012262] device-mapper: dedup-mod: Entered process_bio() function
[ 6167.012263] device-mapper: dedup-mod: Entered handle_read() function
  • 1
    how do you observe this? relevant commands and output? (one example for unexpected read requests is background scanning for UUIDs) – frostschutz Apr 10 at 20:57
  • I used dmesg (I have cleared it before setting up the target). After the above dd command, I can see that there is 1 bio with write direction, and 10 with read direction. – bvsravikiran Apr 10 at 21:07

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