On Mon, Mar 25, 2013 at 11:49:41PM +0000, Richard W.M. Jones wrote:
> From: "Richard W.M. Jones" <rjo...@redhat.com>
>
> qemu-system-x86_64 -drive file=ssh://hostname/some/image
>
> QEMU will ssh into 'hostname' and open '/some/image' which is made
> available as a standard block device.
>
> You can specify a username (ssh://user@host/...) and/or a port number
> (ssh://host:port/...).
>
> Current limitations:
>
> - Authentication must be done without passwords or passphrases, using
> ssh-agent. Other authentication methods are not supported. (*)
>
> - Does not check host key. (*)
>
> - New remote files cannot be created. (*)
>
> - Uses a single connection, instead of concurrent AIO with multiple
> SSH connections.
>
> - Blocks during connection and authentication.
This isn't ideal but .bdrv_open() is a blocking function anyway. If you
open a raw image on an NFS export the open(2) call can block too.
Blocking in .bdrv_open() is fine during startup. It's bad when
hotplugging drives since the running VM will experience downtime.
> + /* Start SFTP. */
> + s->sftp = libssh2_sftp_init(s->session);
> + if (!s->sftp) {
> + session_error_report(s, "failed to initialize sftp handle");
> + ret = -EINVAL;
> + goto err;
> + }
> +
> + s->sftp_handle = libssh2_sftp_open(s->sftp, path,
> + LIBSSH2_FXF_READ|LIBSSH2_FXF_WRITE,
Probably worth handling -drive ...,readonly=on. !(flags & BDRV_O_RDWR)
> +static coroutine_fn void set_fd_handler(BDRVSSHState *s)
> +{
> + int r;
> + void (*rd_handler)(void*);
> + void (*wr_handler)(void*);
There's a typedef for this: IOHandler.
> + Coroutine *co = qemu_coroutine_self();
> +
> + rd_handler = wr_handler = NULL;
> +
> + r = libssh2_session_block_directions(s->session);
> +
> + if (r & LIBSSH2_SESSION_BLOCK_INBOUND) {
> + rd_handler = restart_coroutine;
> + }
> + if (r & LIBSSH2_SESSION_BLOCK_OUTBOUND) {
> + wr_handler = restart_coroutine;
> + }
> +
> + DPRINTF("s->sock=%d rd_handler=%p wr_handler=%p", s->sock,
> + rd_handler, wr_handler);
> +
> + qemu_aio_set_fd_handler(s->sock, rd_handler, wr_handler, return_true,
> co);
> +}
> +
> +/* A non-blocking call returned EAGAIN, so yield, ensuring the
> + * handlers are set up so that we'll be rescheduled when there is an
> + * interesting event on the socket.
> + */
> +static coroutine_fn void co_yield(BDRVSSHState *s)
> +{
> + set_fd_handler(s);
> + qemu_coroutine_yield();
Should we clear the fd handler here? That way the caller doesn't have
to worry about fd handler state.
