Invalid JSON output containing "Input/output error"

[sbraz]

Please acknowledge the following before creating a ticket

• I have read the GitHub issues section of REPORTING-BUGS.

Description of the bug:
Hi,
I noticed that when certain errors occur, the output file contains invalid JSON.

Environment: Debian 10, kernel 6.1.51

fio version: master branch at f53eaac

Reproduction steps

root@localhost ~/fio-master # ./fio --norandommap --time_based --runtime="30s" --readwrite=randrw --numjobs=1 --thread --name=test --group_reporting --output-format=json --output="sdb.log" --filename="/dev/sdb"                                     
fio: io_u error on file /dev/sdb: Input/output error: read offset=184912257024, buflen=4096
root@localhost ~/fio-master # head sdb.log
fio: io_u error on file /dev/sdb: Input/output error: read offset=184912257024, buflen=4096
fio: pid=5509, err=5/file:io_u.c:1896, func=io_u error, error=Input/output error
{
  "fio version" : "fio-3.36",
  "timestamp" : 1702479026,
  "timestamp_ms" : 1702479026165,
  "time" : "Wed Dec 13 14:50:26 2023",
  "global options" : {
    "runtime" : "30s",
    "rw" : "randrw",

Complete log file:
sdb.log

[vincentkfu]

The problem is that JSON output and other output can be sent to the same destination. We should probably collect all info and error messages and create a new key to store these contents. To work around this problem, just do something like this:

earlephilhower/ezfio@f5e2ef1

[sbraz]

Thanks for the reply. Putting error messages in a separate key would be a good idea indeed. I believe that's what smartctl does for instance.
I applied a similar workaround with sed -n '/^{/,$p' although I wasn't 100% comfortable with it as I wasn't sure that errors would always appear before the JSON.