Re: [Qemu-devel] [PATCH] add file: migration support (r2)

[Jamie Lokier]

Charles Duffy wrote:
> documents the limitations of O_NONBLOCK on Linux with local
> filesystem access.

That's not a Linux limitation.

All OSes ignore O_NONBLOCK for filesystem accesses, including remote
filesystems.  This is a POSIX thing.

The reason is that there's no way to select() on a file.  (You'd need
to select() on readiness to read/write a specific byte range anyway,
so the interface doesn't work.)

The nearest equivalent to select() on file I/O is AIO, which is
probably what should be used if migration file I/O is blocking QEMU.

-- Jamie