Am 21.03.2013 um 14:38 hat Richard W.M. Jones geschrieben:
> 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. (*)
Maybe you can just expose it as an encrypted image in order to allow
password authentication?
> - Does not check host key. (*)
>
> - New remote files cannot be created. (*)
>
> - Uses coroutine read/write, instead of true AIO. (libssh2 supports
> non-blocking access, so this could be fixed with some effort).
>
> - Blocks during connection and authentication.
>
> (*) = potentially easy fix
>
> This is implemented using libssh2 on the client side. The server just
> requires a regular ssh daemon with sftp-server support. Most ssh
> daemons on Unix/Linux systems will work out of the box.
> --- /dev/null
> +++ b/block/ssh.c
> @@ -0,0 +1,514 @@
> +/*
> + * Secure Shell (ssh) backend for QEMU.
> + *
> + * Copyright (C) 2013 Red Hat Inc., Richard W.M. Jones <rjo...@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
Please consider the MIT license or LGPL for block layer code; otherwise
we may have to compile the driver out for a future libqblock.
> +
> +#define SECTOR_SIZE 512
BDRV_SECTOR_SIZE exists.
> +
> +static void __attribute__((constructor)) ssh_init(void)
> +{
> + int r;
> +
> + r = libssh2_init(0);
> + if (r != 0) {
> + fprintf(stderr, "libssh2 initialization failed, %d\n", r);
> + exit(EXIT_FAILURE);
> + }
> +}
Why don't you include this in bdrv_ssh_init()?
> +static int parse_uri(BDRVSSHState *s, const char *filename)
> +{
> + URI *uri;
> +
> + uri = uri_parse(filename);
> + if (!uri)
> + return -EINVAL;
> +
> + if (strcmp(uri->scheme, "ssh") != 0) {
> + error_report("URI scheme must be 'ssh'");
> + goto err;
> + }
> +
> + if (!uri->server || strcmp(uri->server, "") == 0) {
> + error_report("missing hostname in URI");
> + goto err;
> + }
> +
> + if (!uri->path || strcmp(uri->path, "") == 0) {
> + error_report("missing remote path in URI");
> + goto err;
> + }
> +
> + /* If user is defined in the URI, use it. Else use local username. */
> + if(uri->user && strcmp(uri->user, "") != 0)
> + s->user = g_strdup(uri->user);
> + else {
> + s->user = get_username();
> + if (!s->user)
> + goto err;
> + }
> +
> + /* Construct the hostname:port string for inet_connect. */
> + if(uri->port == 0)
> + uri->port = 22;
> + s->host = g_strdup_printf("%s:%d", uri->server, uri->port);
> +
> + s->path = g_strdup(uri->path);
> +
> + return 0;
> +
> + err:
> + uri_free(uri);
> + return -EINVAL;
> +}
You could implement this similar to what I just changed in NBD, using
the new .bdrv_parse_filename callback and driver-specific options, so
that instead of specifying a URL you can use something like:
-drive file.driver=ssh,file.host=localhost,file.user=test
This should turn out much more elegant than management tools encoding
everything in a single filename string and qemu parsing it again,
especially once QMP support passing this as JSON objects.
> +static int ssh_file_open(BlockDriverState *bs, const char *filename,
> + int bdrv_flags)
After rebasing, this will have a new parameter for driver-specific
options.
> + ret = parse_uri(s, filename);
> + if (ret < 0)
> + goto err;
I only see it now, but it seems to be repeated all over the place: The
qemu coding style requires braces here.
> +
> + /* Open the socket and connect. */
> + s->sock = inet_connect(s->host, &err);
> + if (err != NULL) {
> + ret = -errno;
> + qerror_report_err(err);
> + error_free(err);
> + goto err;
> + }
> +
> + /* Start up SSH. */
> + ret = connect_to_ssh(s);
> + if (ret < 0)
> + goto err;
> +
> +#if 0 /* Enable this when AIO callbacks are implemented. */
> + /* Go non-blocking. */
> + libssh2_session_set_blocking(s->session, 0);
> +#endif
> +
> + qemu_co_mutex_init(&s->lock);
> +
> + return 0;
> +
> + err:
> + if (s->sock >= 0)
> + close(s->sock);
> + s->sock = -1;
> +
> + g_free(s->path);
> + s->path = NULL;
> + g_free(s->host);
> + s->host = NULL;
> + g_free(s->user);
> + s->user = NULL;
Resetting the fields isn't really necessary. s will be freed anyway.
> +static BlockDriver bdrv_ssh = {
> + .format_name = "ssh",
> + .protocol_name = "ssh",
> + .instance_size = sizeof(BDRVSSHState),
> + .bdrv_file_open = ssh_file_open,
> + .bdrv_close = ssh_close,
> + .bdrv_read = ssh_co_read,
> + .bdrv_write = ssh_co_write,
> + .bdrv_getlength = ssh_getlength,
> +#if 0
> + .bdrv_aio_readv = ssh_aio_readv,
> + .bdrv_aio_writev = ssh_aio_writev,
> + .bdrv_aio_flush = ssh_aio_flush,
> +#endif
> +};
You don't have a bdrv_co_flush_to_disk, what does this mean? Is every
write immediately flushed to the disk, is the driver unsafe by design,
or is this just a missing implementation detail?
Kevin
