Questions on liburing usage

[Ravishankar N <ravishankar@redhat.com>]

Hi,

I have a couple of questions on liburing usage. I hope this is an 
appropriate place to ask.

1.If we perform a io_uring_get_sqe()--> 
io_uring_prep_$FILE_OPERATION()--> io_uring_submit() in sequence, does 
the call to io_uring_submit() ever return a zero? If yes, does it mean 
the sqe submission was not successful and a completion event won't be 
triggered for it?

2. The programs in liburing/examples call io_uring_submit() once a 
significant no. of sqes are got and prepped. Is it an anti-pattern to 
call submit once for each sqe instead of aggregating them and calling 
submit periodically? Especially if the sqes perform operations on 
different files/ file descriptors?

3. Is there any way to examine cqe members using gdb? I get memory 
access errors when I try to.

4. If we get short reads/writes in a cqe, is it because the 
filesystem/device did partial I/O or is it something inherent in using 
the io_uring framework (or any non-blocking I/O method in general)?

5. Is it okay to mix synchronous and uring based operations on the same 
fd, especially if the fd is *not* opened with O_DIRECT?

6. Not really a question but examples/io_uring-cp.c seems to be buggy in 
doing the copy.

 >>>

$ ls -lh FILE
-rw-rw-r--. 1 ravi ravi 100M Apr 28 21:10 FILE

$ md5sum FILE
c2b8ac1f18e65379cc2ab45f8a5f915e  FILE

$ examples/io_uring-cp FILE NEWFILE

$ md5sum NEWFILE
50a9df1f3676bc2c84c67da43022d7bd  NEWFILE

$ ll FILE
-rw-rw-r--. 1 ravi ravi 104857600 Apr 28 21:10 FILE
$ ll NEWFILE
-rw-r--r--. 1 ravi ravi 102858752 Apr 28 21:11 NEWFILE

 >>>

Any help is appreciated.
Regards,
Ravi