Jeff, Blaisor, you're exactly right.  Linux aio uses io_submit, not 
aio_read, it seems.  aio_read calls clone to make a new thread to do its 
"aio".  Thank you all for your help.
Allan

Jeff Dike wrote:

>>Tracing the aio_read() through the UML kernel finally gets me here:
>>
>>#0  sys_pread64 (fd=3, buf=0xbf7c8f20 "", count=1024, pos=0)
>>  at fs/read_write.c:354
>>#1  0x08062ff8 in execute_syscall_skas (r=0x12374864)
>>  at arch/um/kernel/skas/syscall_kern.c:29
>>    
>>
>
>Finally?  That's the very beginning of the system call (or the very end).
>
>The UML block device doesn't know about AIO.  All it does is get blocks from
>a disk.
>
>Are you sure you're getting kernel AIO and not the libc emulation of it?
>
>				Jeff
>  
>