[robespierre]

Interesting - I'm curious what exact revision you're looking at, but the copy on Bitsavers (PDF pg. 228) lists aioread() etc., while the modern documentation has it as aio_read() etc. - and the arguments for each are substantially different (the modern POSIX version takes a pointer to a separate control-block structure, while the SunOS version takes the arguments individually.) Wonder how this evolved over time...

You have a keener eye than me! The hardcopy manual for aioread() etc says "Last updated 21 January 1990".
Solaris's manpage for aio_read() says: "Solaris 2.6 was the first release to support the Asynchronous Input and Output option. Prior to this release, this function always returned −1 and set errno to ENOSYS." I think this only refers to the POSIX version.
Another difference is that SunOS 4's aioread() etc require the libaio library and the <sys/asynch.h> header. Solaris 2.6's aio_read() etc require librt and <aio.h>.