[Qemu-devel] [PATCH v9 1/3] block: Add support for Secure Shell (ssh) block device.

[Qemu-devel] [PATCH v9 1/3] block: Add support for Secure Shell (ssh) block device.

[Richard W.M. Jones]

Changes since v8:

- Implement the suggestions of Stefan Hajnoczi.

- Add host_key_check parameter, which you can use like this:

  ssh://[...]?host_key_check=no     # skip the check entirely
  ssh://[...]?host_key_check=yes    # the default, uses known_hosts

  # or check for a specific host key fingerprint:
  ssh://[...]?host_key_check=md5:<usual SSH host key fingerprint>
  ssh://[...]?host_key_check=sha1:<SHA1 fingerprint>

Note that I cannot persuade OpenSSH to display the SHA1 fingerprint of
a host key, so sha1: is not tested.

A possible extension to this would be to check for the exact key (not
the fingerprint, which is just a hash of the key), although in this
case the URI would be very long indeed, possibly longer than URIs are
supposed to be in some cases.

Rich.

[Qemu-devel] [PATCH v9 1/3] block: Add support for Secure Shell (ssh) block device.

[Richard W.M. Jones]

From: "Richard W.M. Jones" <rjones@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/...).  You can also use an alternate syntax using
properties (file.user, file.host, file.port, file.path).

Current limitations:

- Authentication must be done without passwords or passphrases, using
  ssh-agent.  Other authentication methods are not supported.

- Uses a single connection, instead of concurrent AIO with multiple
  SSH connections.

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.

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>
---
 block/Makefile.objs |   1 +
 block/ssh.c         | 995 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 configure           |  48 +++
 qemu-doc.texi       |  49 +++
 qemu-options.hx     |  12 +
 5 files changed, 1105 insertions(+)
 create mode 100644 block/ssh.c

diff --git a/block/Makefile.objs b/block/Makefile.objs
index c067f38..6c4b5bc 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -13,6 +13,7 @@ block-obj-$(CONFIG_LIBISCSI) += iscsi.o
 block-obj-$(CONFIG_CURL) += curl.o
 block-obj-$(CONFIG_RBD) += rbd.o
 block-obj-$(CONFIG_GLUSTERFS) += gluster.o
+block-obj-$(CONFIG_LIBSSH2) += ssh.o
 endif
 
 common-obj-y += stream.o
diff --git a/block/ssh.c b/block/ssh.c
new file mode 100644
index 0000000..89a9017
--- /dev/null
+++ b/block/ssh.c
@@ -0,0 +1,995 @@
+/*
+ * Secure Shell (ssh) backend for QEMU.
+ *
+ * Copyright (C) 2013 Red Hat Inc., Richard W.M. Jones <rjones@redhat.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+
+#include <libssh2.h>
+#include <libssh2_sftp.h>
+
+#include "block/block_int.h"
+#include "qemu/sockets.h"
+#include "qemu/uri.h"
+#include "qapi/qmp/qint.h"
+
+/* DEBUG_SSH=1 enables the DPRINTF (debugging printf) statements in
+ * this block driver code.
+ *
+ * TRACE_LIBSSH2=<bitmask> enables tracing in libssh2 itself.  Note
+ * that this requires that libssh2 was specially compiled with the
+ * `./configure --enable-debug' option, so most likely you will have
+ * to compile it yourself.  The meaning of <bitmask> is described
+ * here: http://www.libssh2.org/libssh2_trace.html
+ */
+#define DEBUG_SSH     0
+#define TRACE_LIBSSH2 0 /* or try: LIBSSH2_TRACE_SFTP */
+
+#define DPRINTF(fmt, ...)                           \
+    do {                                            \
+        if (DEBUG_SSH) {                            \
+            fprintf(stderr, "ssh: %-15s " fmt "\n", \
+                    __func__, ##__VA_ARGS__);       \
+        }                                           \
+    } while (0)
+
+typedef struct BDRVSSHState {
+    /* Coroutine. */
+    CoMutex lock;
+
+    /* SSH connection. */
+    int sock;                         /* socket */
+    LIBSSH2_SESSION *session;         /* ssh session */
+    LIBSSH2_SFTP *sftp;               /* sftp session */
+    LIBSSH2_SFTP_HANDLE *sftp_handle; /* sftp remote file handle */
+
+    /* See ssh_seek() function below. */
+    int64_t offset;
+    bool offset_op_read;
+
+    /* File attributes at open.  We try to keep the .filesize field
+     * updated if it changes (eg by writing at the end of the file).
+     */
+    LIBSSH2_SFTP_ATTRIBUTES attrs;
+} BDRVSSHState;
+
+static void ssh_state_init(BDRVSSHState *s)
+{
+    memset(s, 0, sizeof *s);
+    s->sock = -1;
+    s->offset = -1;
+    qemu_co_mutex_init(&s->lock);
+}
+
+static void ssh_state_free(BDRVSSHState *s)
+{
+    if (s->sftp_handle) {
+        libssh2_sftp_close(s->sftp_handle);
+    }
+    if (s->sftp) {
+        libssh2_sftp_shutdown(s->sftp);
+    }
+    if (s->session) {
+        libssh2_session_disconnect(s->session,
+                                   "from qemu ssh client: "
+                                   "user closed the connection");
+        libssh2_session_free(s->session);
+    }
+    if (s->sock >= 0) {
+        close(s->sock);
+    }
+}
+
+/* Wrappers around error_report which make sure to dump as much
+ * information from libssh2 as possible.
+ */
+static void
+session_error_report(BDRVSSHState *s, const char *fs, ...)
+{
+    va_list args;
+
+    va_start(args, fs);
+    error_vprintf(fs, args);
+
+    if ((s)->session) {
+        char *ssh_err;
+        int ssh_err_code;
+
+        libssh2_session_last_error((s)->session, &ssh_err, NULL, 0);
+        /* This is not an errno.  See <libssh2.h>. */
+        ssh_err_code = libssh2_session_last_errno((s)->session);
+
+        error_printf(": %s (libssh2 error code: %d)", ssh_err, ssh_err_code);
+    }
+
+    va_end(args);
+    error_printf("\n");
+}
+
+static void
+sftp_error_report(BDRVSSHState *s, const char *fs, ...)
+{
+    va_list args;
+
+    va_start(args, fs);
+    error_vprintf(fs, args);
+
+    if ((s)->sftp) {
+        char *ssh_err;
+        int ssh_err_code;
+        unsigned long sftp_err_code;
+
+        libssh2_session_last_error((s)->session, &ssh_err, NULL, 0);
+        /* This is not an errno.  See <libssh2.h>. */
+        ssh_err_code = libssh2_session_last_errno((s)->session);
+        /* See <libssh2_sftp.h>. */
+        sftp_err_code = libssh2_sftp_last_error((s)->sftp);
+
+        error_printf(": %s (libssh2 error code: %d, sftp error code: %lu)",
+                     ssh_err, ssh_err_code, sftp_err_code);
+    }
+
+    va_end(args);
+    error_printf("\n");
+}
+
+static int parse_uri(const char *filename, QDict *options, Error **errp)
+{
+    URI *uri = NULL;
+    QueryParams *qp = NULL;
+    int i;
+
+    uri = uri_parse(filename);
+    if (!uri) {
+        return -EINVAL;
+    }
+
+    if (strcmp(uri->scheme, "ssh") != 0) {
+        error_setg(errp, "URI scheme must be 'ssh'");
+        goto err;
+    }
+
+    if (!uri->server || strcmp(uri->server, "") == 0) {
+        error_setg(errp, "missing hostname in URI");
+        goto err;
+    }
+
+    if (!uri->path || strcmp(uri->path, "") == 0) {
+        error_setg(errp, "missing remote path in URI");
+        goto err;
+    }
+
+    qp = query_params_parse(uri->query);
+    if (!qp) {
+        error_setg(errp, "could not parse query parameters");
+        goto err;
+    }
+
+    if(uri->user && strcmp(uri->user, "") != 0) {
+        qdict_put(options, "user", qstring_from_str(uri->user));
+    }
+
+    qdict_put(options, "host", qstring_from_str(uri->server));
+
+    if (uri->port) {
+        qdict_put(options, "port", qint_from_int(uri->port));
+    }
+
+    qdict_put(options, "path", qstring_from_str(uri->path));
+
+    /* Pick out any query parameters that we understand, and ignore
+     * the rest.
+     */
+    for (i = 0; i < qp->n; ++i) {
+        if (strcmp(qp->p[i].name, "host_key_check") == 0) {
+            qdict_put(options, "host_key_check",
+                      qstring_from_str(qp->p[i].value));
+        }
+    }
+
+    query_params_free(qp);
+    uri_free(uri);
+    return 0;
+
+ err:
+    if (qp) {
+      query_params_free(qp);
+    }
+    if (uri) {
+      uri_free(uri);
+    }
+    return -EINVAL;
+}
+
+static void ssh_parse_filename(const char *filename, QDict *options,
+                               Error **errp)
+{
+    if (qdict_haskey(options, "user") ||
+        qdict_haskey(options, "host") ||
+        qdict_haskey(options, "port") ||
+        qdict_haskey(options, "path") ||
+        qdict_haskey(options, "host_key_check")) {
+        error_setg(errp, "user, host, port, path, host_key_check cannot be used at the same time as a file option");
+        return;
+    }
+
+    parse_uri(filename, options, errp);
+}
+
+static int check_host_key_knownhosts(BDRVSSHState *s,
+                                     const char *host, int port)
+{
+    const char *home;
+    char *knh_file = NULL;
+    LIBSSH2_KNOWNHOSTS *knh = NULL;
+    struct libssh2_knownhost *found;
+    int ret, r;
+    const char *hostkey;
+    size_t len;
+    int type;
+
+    hostkey = libssh2_session_hostkey(s->session, &len, &type);
+    if (!hostkey) {
+        ret = -EINVAL;
+        session_error_report(s, "failed to read remote host key");
+        goto out;
+    }
+
+    knh = libssh2_knownhost_init(s->session);
+    if (!knh) {
+        ret = -EINVAL;
+        session_error_report(s, "failed to initialize known hosts support");
+        goto out;
+    }
+
+    home = getenv("HOME");
+    if (home) {
+        knh_file = g_strdup_printf("%s/.ssh/known_hosts", home);
+    } else {
+        knh_file = g_strdup_printf("/root/.ssh/known_hosts");
+    }
+
+    /* Read all known hosts from OpenSSH-style known_hosts file. */
+    libssh2_knownhost_readfile(knh, knh_file, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
+
+    r = libssh2_knownhost_checkp(knh, host, port, hostkey, len,
+                                 LIBSSH2_KNOWNHOST_TYPE_PLAIN|
+                                 LIBSSH2_KNOWNHOST_KEYENC_RAW,
+                                 &found);
+    switch (r) {
+    case LIBSSH2_KNOWNHOST_CHECK_MATCH:
+        /* OK */
+        DPRINTF("host key OK: %s", found->key);
+        break;
+    case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
+        ret = -EINVAL;
+        session_error_report(s, "host key does not match the one in known_hosts (found key %s)",
+                             found->key);
+        goto out;
+    case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
+        ret = -EINVAL;
+        session_error_report(s, "no host key was found in known_hosts");
+        goto out;
+    case LIBSSH2_KNOWNHOST_CHECK_FAILURE:
+        ret = -EINVAL;
+        session_error_report(s, "failure matching the host key with known_hosts");
+        goto out;
+    default:
+        ret = -EINVAL;
+        session_error_report(s, "unknown error matching the host key with known_hosts (%d)",
+                             r);
+        goto out;
+    }
+
+    /* known_hosts checking successful. */
+    ret = 0;
+
+ out:
+    if (knh != NULL) {
+        libssh2_knownhost_free(knh);
+    }
+    g_free(knh_file);
+    return ret;
+}
+
+static unsigned hex2decimal(char ch)
+{
+    if (ch >= '0' && ch <= '9') {
+        return (ch - '0');
+    } else if (ch >= 'a' && ch <= 'f') {
+        return 10 + (ch - 'a');
+    } else if (ch >= 'A' && ch <= 'F') {
+        return 10 + (ch - 'A');
+    }
+
+    return -1;
+}
+
+/* Compare the binary fingerprint (hash of host key) with the
+ * host_key_check parameter.
+ */
+static int compare_fingerprint(const unsigned char *fingerprint, size_t len,
+                               const char *host_key_check)
+{
+    unsigned c;
+
+    while (len > 0) {
+        while (*host_key_check == ':')
+            host_key_check++;
+        if (!qemu_isxdigit(host_key_check[0]) ||
+            !qemu_isxdigit(host_key_check[1]))
+            return 1;
+        c = hex2decimal(host_key_check[0]) * 16 +
+            hex2decimal(host_key_check[1]);
+        if (c - *fingerprint != 0)
+            return c - *fingerprint;
+        fingerprint++;
+        len--;
+        host_key_check += 2;
+    }
+    return *host_key_check - '\0';
+}
+
+static int
+check_host_key_hash(BDRVSSHState *s, const char *hash,
+                    int hash_type, size_t fingerprint_len)
+{
+    const char *fingerprint;
+
+    fingerprint = libssh2_hostkey_hash(s->session, hash_type);
+    if (!fingerprint) {
+        session_error_report(s, "failed to read remote host key");
+        return -EINVAL;
+    }
+
+    if(compare_fingerprint((unsigned char *) fingerprint, fingerprint_len,
+                           hash) != 0) {
+        error_report("remote host key does not match host_key_check '%s'",
+                     hash);
+        return -EPERM;
+    }
+
+    return 0;
+}
+
+static int check_host_key(BDRVSSHState *s, const char *host, int port,
+                          const char *host_key_check)
+{
+    /* host_key_check=no */
+    if (strcmp(host_key_check, "no") == 0) {
+        return 0;
+    }
+
+    /* host_key_check=md5:xx:yy:zz:... */
+    if (strlen(host_key_check) >= 4 &&
+        strncmp(host_key_check, "md5:", 4) == 0) {
+        return check_host_key_hash(s, &host_key_check[4],
+                                   LIBSSH2_HOSTKEY_HASH_MD5, 16);
+    }
+
+    /* host_key_check=sha1:xx:yy:zz:... */
+    if (strlen(host_key_check) >= 5 &&
+        strncmp(host_key_check, "sha1:", 5) == 0) {
+        return check_host_key_hash(s, &host_key_check[5],
+                                   LIBSSH2_HOSTKEY_HASH_SHA1, 20);
+    }
+
+    /* host_key_check=yes */
+    if (strcmp(host_key_check, "yes") == 0) {
+        return check_host_key_knownhosts(s, host, port);
+    }
+
+    error_report("unknown host_key_check setting (%s)", host_key_check);
+    return -EINVAL;
+}
+
+static int authenticate(BDRVSSHState *s, const char *user)
+{
+    int r, ret;
+    const char *userauthlist;
+    LIBSSH2_AGENT *agent = NULL;
+    struct libssh2_agent_publickey *identity;
+    struct libssh2_agent_publickey *prev_identity = NULL;
+
+    userauthlist = libssh2_userauth_list(s->session, user, strlen(user));
+    if (strstr(userauthlist, "publickey") == NULL) {
+        ret = -EPERM;
+        error_report("remote server does not support \"publickey\" authentication");
+        goto out;
+    }
+
+    /* Connect to ssh-agent and try each identity in turn. */
+    agent = libssh2_agent_init(s->session);
+    if (!agent) {
+        ret = -EINVAL;
+        session_error_report(s, "failed to initialize ssh-agent support");
+        goto out;
+    }
+    if (libssh2_agent_connect(agent)) {
+        ret = -ECONNREFUSED;
+        session_error_report(s, "failed to connect to ssh-agent");
+        goto out;
+    }
+    if (libssh2_agent_list_identities(agent)) {
+        ret = -EINVAL;
+        session_error_report(s, "failed requesting identities from ssh-agent");
+        goto out;
+    }
+
+    for(;;) {
+        r = libssh2_agent_get_identity(agent, &identity, prev_identity);
+        if (r == 1) {           /* end of list */
+            break;
+        }
+        if (r < 0) {
+            ret = -EINVAL;
+            session_error_report(s, "failed to obtain identity from ssh-agent");
+            goto out;
+        }
+        r = libssh2_agent_userauth(agent, user, identity);
+        if (r == 0) {
+            /* Authenticated! */
+            ret = 0;
+            goto out;
+        }
+        /* Failed to authenticate with this identity, try the next one. */
+        prev_identity = identity;
+    }
+
+    ret = -EPERM;
+    error_report("failed to authenticate using publickey authentication "
+                 "and the identities held by your ssh-agent");
+
+ out:
+    if (agent != NULL) {
+        /* Note: libssh2 implementation implicitly calls
+         * libssh2_agent_disconnect if necessary.
+         */
+        libssh2_agent_free(agent);
+    }
+
+    return ret;
+}
+
+static int connect_to_ssh(BDRVSSHState *s, QDict *options,
+                          int ssh_flags, int creat_mode)
+{
+    int r, ret;
+    Error *err = NULL;
+    const char *host, *user, *path, *host_key_check;
+    int port;
+    char *hostport = NULL;
+
+    host = qdict_get_str(options, "host");
+
+    if (qdict_haskey(options, "port")) {
+        port = qdict_get_int(options, "port");
+    } else {
+        port = 22;
+    }
+
+    path = qdict_get_str(options, "path");
+
+    if (qdict_haskey(options, "user")) {
+        user = qdict_get_str(options, "user");
+    } else {
+        user = g_get_user_name();
+        if (!user) {
+            ret = -errno;
+            goto err;
+        }
+    }
+
+    if (qdict_haskey(options, "host_key_check")) {
+        host_key_check = qdict_get_str(options, "host_key_check");
+    } else {
+        host_key_check = "yes";
+    }
+
+    /* Open the socket and connect. */
+    hostport = g_strdup_printf("%s:%d", host, port);
+    s->sock = inet_connect(hostport, &err);
+    if (err != NULL) {
+        ret = -errno;
+        qerror_report_err(err);
+        error_free(err);
+        goto err;
+    }
+
+    /* Create SSH session. */
+    s->session = libssh2_session_init();
+    if (!s->session) {
+        ret = -EINVAL;
+        session_error_report(s, "failed to initialize libssh2 session");
+        goto err;
+    }
+
+#if TRACE_LIBSSH2 != 0
+    libssh2_trace(s->session, TRACE_LIBSSH2);
+#endif
+
+    r = libssh2_session_handshake(s->session, s->sock);
+    if (r != 0) {
+        ret = -EINVAL;
+        session_error_report(s, "failed to establish SSH session");
+        goto err;
+    }
+
+    /* Check the remote host's key against known_hosts. */
+    ret = check_host_key(s, host, port, host_key_check);
+    if (ret < 0) {
+        goto err;
+    }
+
+    /* Authenticate. */
+    ret = authenticate(s, user);
+    if (ret < 0) {
+        goto err;
+    }
+
+    /* 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;
+    }
+
+    /* Open the remote file. */
+    DPRINTF("opening file %s flags=0x%x creat_mode=0%o",
+            path, ssh_flags, creat_mode);
+    s->sftp_handle = libssh2_sftp_open(s->sftp, path, ssh_flags, creat_mode);
+    if (!s->sftp_handle) {
+        session_error_report(s, "failed to open remote file '%s'", path);
+        ret = -EINVAL;
+        goto err;
+    }
+
+    r = libssh2_sftp_fstat(s->sftp_handle, &s->attrs);
+    if (r < 0) {
+        sftp_error_report(s, "failed to read file attributes");
+        return -EINVAL;
+    }
+
+    /* Delete the options we've used; any not deleted will cause the
+     * block layer to give an error about unused options.
+     */
+    qdict_del(options, "host");
+    qdict_del(options, "port");
+    qdict_del(options, "user");
+    qdict_del(options, "path");
+    qdict_del(options, "host_key_check");
+
+    g_free(hostport);
+    return 0;
+
+ err:
+    if (s->sftp_handle) {
+        libssh2_sftp_close(s->sftp_handle);
+    }
+    s->sftp_handle = NULL;
+    if (s->sftp) {
+        libssh2_sftp_shutdown(s->sftp);
+    }
+    s->sftp = NULL;
+    if (s->session) {
+        libssh2_session_disconnect(s->session,
+                                   "from qemu ssh client: "
+                                   "error opening connection");
+        libssh2_session_free(s->session);
+    }
+    s->session = NULL;
+    g_free(hostport);
+
+    return ret;
+}
+
+static int ssh_file_open(BlockDriverState *bs, const char *filename,
+                         QDict *options, int bdrv_flags)
+{
+    BDRVSSHState *s = bs->opaque;
+    int ret;
+    int ssh_flags;
+
+    ssh_state_init(s);
+
+    ssh_flags = LIBSSH2_FXF_READ;
+    if (bdrv_flags & BDRV_O_RDWR) {
+        ssh_flags |= LIBSSH2_FXF_WRITE;
+    }
+
+    /* Start up SSH. */
+    ret = connect_to_ssh(s, options, ssh_flags, 0);
+    if (ret < 0) {
+        goto err;
+    }
+
+    /* Go non-blocking. */
+    libssh2_session_set_blocking(s->session, 0);
+
+    return 0;
+
+ err:
+    if (s->sock >= 0) {
+        close(s->sock);
+    }
+    s->sock = -1;
+
+    return ret;
+}
+
+static QEMUOptionParameter ssh_create_options[] = {
+    {
+        .name = BLOCK_OPT_SIZE,
+        .type = OPT_SIZE,
+        .help = "Virtual disk size"
+    },
+    { NULL }
+};
+
+static int ssh_create(const char *filename, QEMUOptionParameter *options)
+{
+    int r, ret;
+    Error *local_err = NULL;
+    int64_t total_size = 0;
+    QDict *uri_options = NULL;
+    BDRVSSHState s;
+    ssize_t r2;
+    char c[1] = { '\0' };
+
+    ssh_state_init(&s);
+
+    /* Get desired file size. */
+    while (options && options->name) {
+        if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
+            total_size = options->value.n;
+        }
+        options++;
+    }
+    DPRINTF("total_size=%" PRIi64, total_size);
+
+    uri_options = qdict_new();
+    r = parse_uri(filename, uri_options, &local_err);
+    if (r < 0) {
+        qerror_report_err(local_err);
+        error_free(local_err);
+        ret = r;
+        goto out;
+    }
+
+    r = connect_to_ssh(&s, uri_options,
+                       LIBSSH2_FXF_READ|LIBSSH2_FXF_WRITE|
+                       LIBSSH2_FXF_CREAT|LIBSSH2_FXF_TRUNC, 0644);
+    if (r < 0) {
+        ret = r;
+        goto out;
+    }
+
+    if (total_size > 0) {
+        libssh2_sftp_seek64(s.sftp_handle, total_size-1);
+        r2 = libssh2_sftp_write(s.sftp_handle, c, 1);
+        if (r2 < 0) {
+            sftp_error_report(&s, "truncate failed");
+            ret = -EINVAL;
+            goto out;
+        }
+        s.attrs.filesize = total_size;
+    }
+
+    ret = 0;
+
+ out:
+    ssh_state_free(&s);
+    if (uri_options != NULL) {
+        QDECREF(uri_options);
+    }
+    return ret;
+}
+
+static void ssh_close(BlockDriverState *bs)
+{
+    BDRVSSHState *s = bs->opaque;
+
+    ssh_state_free(s);
+}
+
+static void restart_coroutine(void *opaque)
+{
+    Coroutine *co = opaque;
+
+    DPRINTF("co=%p", co);
+
+    qemu_coroutine_enter(co, NULL);
+}
+
+/* Always true because when we have called set_fd_handler there is
+ * always a request being processed.
+ */
+static int return_true(void *opaque)
+{
+    return 1;
+}
+
+static coroutine_fn void set_fd_handler(BDRVSSHState *s)
+{
+    int r;
+    IOHandler *rd_handler = NULL, *wr_handler = NULL;
+    Coroutine *co = qemu_coroutine_self();
+
+    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);
+}
+
+static coroutine_fn void clear_fd_handler(BDRVSSHState *s)
+{
+    DPRINTF("s->sock=%d", s->sock);
+    qemu_aio_set_fd_handler(s->sock, NULL, NULL, NULL, NULL);
+}
+
+/* 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();
+    clear_fd_handler(s);
+}
+
+/* SFTP has a function `libssh2_sftp_seek64' which seeks to a position
+ * in the remote file.  Notice that it just updates a field in the
+ * sftp_handle structure, so there is no network traffic and it cannot
+ * fail.
+ *
+ * However, `libssh2_sftp_seek64' does have a catastrophic effect on
+ * performance since it causes the handle to throw away all in-flight
+ * reads and buffered readahead data.  Therefore this function tries
+ * to be intelligent about when to call the underlying libssh2 function.
+ */
+#define SSH_SEEK_WRITE 0
+#define SSH_SEEK_READ  1
+#define SSH_SEEK_FORCE 2
+
+static void ssh_seek(BDRVSSHState *s, int64_t offset, int flags)
+{
+    bool op_read = (flags & SSH_SEEK_READ) != 0;
+    bool force = (flags & SSH_SEEK_FORCE) != 0;
+
+    if (force || op_read != s->offset_op_read || offset != s->offset) {
+        DPRINTF("seeking to offset=%" PRIi64, offset);
+        libssh2_sftp_seek64(s->sftp_handle, offset);
+        s->offset = offset;
+        s->offset_op_read = op_read;
+    }
+}
+
+static coroutine_fn int ssh_read(BDRVSSHState *s,
+                                 int64_t offset, size_t size,
+                                 QEMUIOVector *qiov)
+{
+    ssize_t r;
+    size_t got;
+    char *buf, *end_of_vec;
+    struct iovec *i;
+
+    DPRINTF("offset=%" PRIi64 " size=%zu", offset, size);
+
+    ssh_seek(s, offset, SSH_SEEK_READ);
+
+    /* This keeps track of the current iovec element ('i'), where we
+     * will write to next ('buf'), and the end of the current iovec
+     * ('end_of_vec').
+     */
+    i = &qiov->iov[0];
+    buf = i->iov_base;
+    end_of_vec = i->iov_base + i->iov_len;
+
+    /* libssh2 has a hard-coded limit of 2000 bytes per request,
+     * although it will also do readahead behind our backs.  Therefore
+     * we may have to do repeated reads here until we have read 'size'
+     * bytes.
+     */
+    for (got = 0; got < size; ) {
+    again:
+        DPRINTF("sftp_read buf=%p size=%zu", buf, end_of_vec - buf);
+        r = libssh2_sftp_read(s->sftp_handle, buf, end_of_vec - buf);
+        DPRINTF("sftp_read returned %zd", r);
+
+        if (r == LIBSSH2_ERROR_EAGAIN || r == LIBSSH2_ERROR_TIMEOUT) {
+            co_yield(s);
+            goto again;
+        }
+        if (r < 0) {
+            sftp_error_report(s, "read failed");
+            s->offset = -1;
+            return -EIO;
+        }
+        if (r == 0) {
+            /* EOF: Short read so pad the buffer with zeroes and return it. */
+            qemu_iovec_memset(qiov, got, 0, size - got);
+            return 0;
+        }
+
+        got += r;
+        buf += r;
+        s->offset += r;
+        if (buf >= end_of_vec && got < size) {
+            i++;
+            buf = i->iov_base;
+            end_of_vec = i->iov_base + i->iov_len;
+        }
+    }
+
+    return 0;
+}
+
+static coroutine_fn int ssh_co_readv(BlockDriverState *bs,
+                                     int64_t sector_num,
+                                     int nb_sectors, QEMUIOVector *qiov)
+{
+    BDRVSSHState *s = bs->opaque;
+    int ret;
+
+    qemu_co_mutex_lock(&s->lock);
+    ret = ssh_read(s, sector_num * BDRV_SECTOR_SIZE,
+                   nb_sectors * BDRV_SECTOR_SIZE, qiov);
+    qemu_co_mutex_unlock(&s->lock);
+
+    return ret;
+}
+
+static int ssh_write(BDRVSSHState *s,
+                     int64_t offset, size_t size,
+                     QEMUIOVector *qiov)
+{
+    ssize_t r;
+    size_t written;
+    char *buf, *end_of_vec;
+    struct iovec *i;
+
+    DPRINTF("offset=%" PRIi64 " size=%zu", offset, size);
+
+    ssh_seek(s, offset, SSH_SEEK_WRITE);
+
+    /* This keeps track of the current iovec element ('i'), where we
+     * will read from next ('buf'), and the end of the current iovec
+     * ('end_of_vec').
+     */
+    i = &qiov->iov[0];
+    buf = i->iov_base;
+    end_of_vec = i->iov_base + i->iov_len;
+
+    for (written = 0; written < size; ) {
+    again:
+        DPRINTF("sftp_write buf=%p size=%zu", buf, end_of_vec - buf);
+        r = libssh2_sftp_write(s->sftp_handle, buf, end_of_vec - buf);
+        DPRINTF("sftp_write returned %zd", r);
+
+        if (r == LIBSSH2_ERROR_EAGAIN || r == LIBSSH2_ERROR_TIMEOUT) {
+            co_yield(s);
+            goto again;
+        }
+        if (r < 0) {
+            sftp_error_report(s, "write failed");
+            s->offset = -1;
+            return -EIO;
+        }
+        /* The libssh2 API is very unclear about this.  A comment in
+         * the code says "nothing was acked, and no EAGAIN was
+         * received!" which apparently means that no data got sent
+         * out, and the underlying channel didn't return any EAGAIN
+         * indication.  I think this is a bug in either libssh2 or
+         * OpenSSH (server-side).  In any case, forcing a seek (to
+         * discard libssh2 internal buffers), and then trying again
+         * works for me.
+         */
+        if (r == 0) {
+            ssh_seek(s, offset + written, SSH_SEEK_WRITE|SSH_SEEK_FORCE);
+            co_yield(s);
+            goto again;
+        }
+
+        written += r;
+        buf += r;
+        s->offset += r;
+        if (buf >= end_of_vec && written < size) {
+            i++;
+            buf = i->iov_base;
+            end_of_vec = i->iov_base + i->iov_len;
+        }
+
+        if (offset + written > s->attrs.filesize)
+            s->attrs.filesize = offset + written;
+    }
+
+    return 0;
+}
+
+static coroutine_fn int ssh_co_writev(BlockDriverState *bs,
+                                      int64_t sector_num,
+                                      int nb_sectors, QEMUIOVector *qiov)
+{
+    BDRVSSHState *s = bs->opaque;
+    int ret;
+
+    qemu_co_mutex_lock(&s->lock);
+    ret = ssh_write(s, sector_num * BDRV_SECTOR_SIZE,
+                    nb_sectors * BDRV_SECTOR_SIZE, qiov);
+    qemu_co_mutex_unlock(&s->lock);
+
+    return ret;
+}
+
+static int64_t ssh_getlength(BlockDriverState *bs)
+{
+    BDRVSSHState *s = bs->opaque;
+    int64_t length;
+
+    /* Note we cannot make a libssh2 call here. */
+    length = (int64_t) s->attrs.filesize;
+    DPRINTF("length=%" PRIi64, length);
+
+    return length;
+}
+
+static BlockDriver bdrv_ssh = {
+    .format_name                  = "ssh",
+    .protocol_name                = "ssh",
+    .instance_size                = sizeof(BDRVSSHState),
+    .bdrv_parse_filename          = ssh_parse_filename,
+    .bdrv_file_open               = ssh_file_open,
+    .bdrv_create                  = ssh_create,
+    .bdrv_close                   = ssh_close,
+    .bdrv_co_readv                = ssh_co_readv,
+    .bdrv_co_writev               = ssh_co_writev,
+    .bdrv_getlength               = ssh_getlength,
+    .create_options               = ssh_create_options,
+};
+
+static void bdrv_ssh_init(void)
+{
+    int r;
+
+    r = libssh2_init(0);
+    if (r != 0) {
+        fprintf(stderr, "libssh2 initialization failed, %d\n", r);
+        exit(EXIT_FAILURE);
+    }
+
+    bdrv_register(&bdrv_ssh);
+}
+
+block_init(bdrv_ssh_init);
diff --git a/configure b/configure
index 1ed939a..4dd65b0 100755
--- a/configure
+++ b/configure
@@ -239,6 +239,7 @@ virtio_blk_data_plane=""
 gtk=""
 gtkabi="2.0"
 tpm="no"
+libssh2=""
 
 # parse CC options first
 for opt do
@@ -922,6 +923,10 @@ for opt do
   ;;
   --enable-tpm) tpm="yes"
   ;;
+  --disable-libssh2) libssh2="no"
+  ;;
+  --enable-libssh2) libssh2="yes"
+  ;;
   *) echo "ERROR: unknown option $opt"; show_help="yes"
   ;;
   esac
@@ -1182,6 +1187,8 @@ echo "  --disable-glusterfs      disable GlusterFS backend"
 echo "  --enable-gcov            enable test coverage analysis with gcov"
 echo "  --gcov=GCOV              use specified gcov [$gcov_tool]"
 echo "  --enable-tpm             enable TPM support"
+echo "  --disable-libssh2        disable ssh block device support"
+echo "  --enable-libssh2         enable ssh block device support"
 echo ""
 echo "NOTE: The object files are built at the place where configure is launched"
 exit 1
@@ -2314,6 +2321,42 @@ EOF
 fi
 
 ##########################################
+# libssh2 probe
+if test "$libssh2" != "no" ; then
+  cat > $TMPC <<EOF
+#include <stdio.h>
+#include <libssh2.h>
+#include <libssh2_sftp.h>
+int main(void) {
+    LIBSSH2_SESSION *session;
+    session = libssh2_session_init ();
+    (void) libssh2_sftp_init (session);
+    return 0;
+}
+EOF
+
+  if $pkg_config libssh2 --modversion >/dev/null 2>&1; then
+    libssh2_cflags=`$pkg_config libssh2 --cflags`
+    libssh2_libs=`$pkg_config libssh2 --libs`
+  else
+    libssh2_cflags=
+    libssh2_libs="-lssh2"
+  fi
+
+  if compile_prog "$libssh2_cflags" "$libssh2_libs" ; then
+    libssh2=yes
+    libs_tools="$libssh2_libs $libs_tools"
+    libs_softmmu="$libssh2_libs $libs_softmmu"
+    QEMU_CFLAGS="$QEMU_CFLAGS $libssh2_cflags"
+  else
+    if test "$libssh2" = "yes" ; then
+      feature_not_found "libssh2"
+    fi
+    libssh2=no
+  fi
+fi
+
+##########################################
 # linux-aio probe
 
 if test "$linux_aio" != "no" ; then
@@ -3435,6 +3478,7 @@ echo "virtio-blk-data-plane $virtio_blk_data_plane"
 echo "gcov              $gcov_tool"
 echo "gcov enabled      $gcov"
 echo "TPM support       $tpm"
+echo "libssh2 support   $libssh2"
 
 if test "$sdl_too_old" = "yes"; then
 echo "-> Your SDL version is too old - please upgrade to have SDL support"
@@ -3796,6 +3840,10 @@ if test "$glusterfs" = "yes" ; then
   echo "CONFIG_GLUSTERFS=y" >> $config_host_mak
 fi
 
+if test "$libssh2" = "yes" ; then
+  echo "CONFIG_LIBSSH2=y" >> $config_host_mak
+fi
+
 if test "$virtio_blk_data_plane" = "yes" ; then
   echo 'CONFIG_VIRTIO_BLK_DATA_PLANE=$(CONFIG_VIRTIO)' >> $config_host_mak
 fi
diff --git a/qemu-doc.texi b/qemu-doc.texi
index af84bef..5b36004 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -423,6 +423,7 @@ snapshots.
 * disk_images_sheepdog::      Sheepdog disk images
 * disk_images_iscsi::         iSCSI LUNs
 * disk_images_gluster::       GlusterFS disk images
+* disk_images_ssh::           Secure Shell (ssh) disk images
 @end menu
 
 @node disk_images_quickstart
@@ -1038,6 +1039,54 @@ qemu-system-x86_64 -drive file=gluster+unix:///testvol/dir/a.img?socket=/tmp/glu
 qemu-system-x86_64 -drive file=gluster+rdma://1.2.3.4:24007/testvol/a.img
 @end example
 
+@node disk_images_ssh
+@subsection Secure Shell (ssh) disk images
+
+You can access disk images located on a remote ssh server
+by using the ssh protocol:
+
+@example
+qemu-system-x86_64 -drive file=ssh://[@var{user}@@]@var{server}[:@var{port}]/@var{path}[?host_key_check=@var{host_key_check}]
+@end example
+
+Alternative syntax using properties:
+
+@example
+qemu-system-x86_64 -drive file.driver=ssh[,file.user=@var{user}],file.host=@var{server}[,file.port=@var{port}],file.path=@var{path}[,file.host_key_check=@var{host_key_check}]
+@end example
+
+@var{ssh} is the protocol.
+
+@var{user} is the remote user.  If not specified, then the local
+username is tried.
+
+@var{server} specifies the remote ssh server.  Any ssh server can be
+used, but it must implement the sftp-server protocol.  Most Unix/Linux
+systems should work without requiring any extra configuration.
+
+@var{port} is the port number on which sshd is listening.  By default
+the standard ssh port (22) is used.
+
+@var{path} is the path to the disk image.
+
+The optional @var{host_key_check} parameter controls how the remote
+host's key is checked.  The default is @code{yes} which means to use
+the local @file{.ssh/known_hosts} file.  Setting this to @code{no}
+turns off known-hosts checking.  Or you can check that the host key
+matches a specific fingerprint:
+@code{host_key_check=md5:78:45:8e:14:57:4f:d5:45:83:0a:0e:f3:49:82:c9:c8}
+(@code{sha1:} can also be used as a prefix, but note that OpenSSH
+tools only use MD5 to print fingerprints).
+
+Currently authentication must be done using ssh-agent.  Other
+authentication methods may be supported in future.
+
+Note: The ssh driver does not obey disk flush requests (ie. to commit
+data to the backing disk when the guest requests it).  This is because
+the underlying protocol (SFTP) does not support this.  Thus there is a
+risk of guest disk corruption if the remote server or network goes
+down during writes.
+
 @node pcsys_network
 @section Network emulation
 
diff --git a/qemu-options.hx b/qemu-options.hx
index 7cd6002..5c115d1 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2107,6 +2107,18 @@ Example for Unix Domain Sockets
 qemu-system-i386 --drive file=nbd:unix:/tmp/nbd-socket
 @end example
 
+@item SSH
+QEMU supports SSH (Secure Shell) access to remote disks.
+
+Examples:
+@example
+qemu-system-i386 -drive file=ssh://user@@host/path/to/disk.img
+qemu-system-i386 -drive file.driver=ssh,file.user=user,file.host=host,file.port=22,file.path=/path/to/disk.img
+@end example
+
+Currently authentication must be done using ssh-agent.  Other
+authentication methods may be supported in future.
+
 @item Sheepdog
 Sheepdog is a distributed storage system for QEMU.
 QEMU supports using either local sheepdog devices or remote networked
-- 
1.8.1.4

[Qemu-devel] [PATCH v9 2/3] block: ssh: Use libssh2_sftp_fsync (if supported by libssh2) to flush to disk.

[Richard W.M. Jones]

From: "Richard W.M. Jones" <rjones@redhat.com>

libssh2_sftp_fsync is an extension to libssh2 to support fsync(2) over
sftp, which is itself an extension of OpenSSH.

If both libssh2 and the ssh daemon support it, this will allow
bdrv_flush_to_disk to commit changes through to disk on the remote
server.
---
 block/ssh.c   | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 configure     | 25 +++++++++++++++++++
 qemu-doc.texi | 15 ++++++++----
 3 files changed, 108 insertions(+), 10 deletions(-)

diff --git a/block/ssh.c b/block/ssh.c
index 89a9017..8f78e2e 100644
--- a/block/ssh.c
+++ b/block/ssh.c
@@ -72,6 +72,10 @@ typedef struct BDRVSSHState {
      * updated if it changes (eg by writing at the end of the file).
      */
     LIBSSH2_SFTP_ATTRIBUTES attrs;
+
+    /* Used to warn if 'flush' is not supported. */
+    char *hostport;
+    bool unsafe_flush_warning;
 } BDRVSSHState;
 
 static void ssh_state_init(BDRVSSHState *s)
@@ -84,6 +88,7 @@ static void ssh_state_init(BDRVSSHState *s)
 
 static void ssh_state_free(BDRVSSHState *s)
 {
+    g_free(s->hostport);
     if (s->sftp_handle) {
         libssh2_sftp_close(s->sftp_handle);
     }
@@ -479,7 +484,6 @@ static int connect_to_ssh(BDRVSSHState *s, QDict *options,
     Error *err = NULL;
     const char *host, *user, *path, *host_key_check;
     int port;
-    char *hostport = NULL;
 
     host = qdict_get_str(options, "host");
 
@@ -507,9 +511,12 @@ static int connect_to_ssh(BDRVSSHState *s, QDict *options,
         host_key_check = "yes";
     }
 
+    /* Construct the host:port name for inet_connect. */
+    g_free(s->hostport);
+    s->hostport = g_strdup_printf("%s:%d", host, port);
+
     /* Open the socket and connect. */
-    hostport = g_strdup_printf("%s:%d", host, port);
-    s->sock = inet_connect(hostport, &err);
+    s->sock = inet_connect(s->hostport, &err);
     if (err != NULL) {
         ret = -errno;
         qerror_report_err(err);
@@ -581,7 +588,6 @@ static int connect_to_ssh(BDRVSSHState *s, QDict *options,
     qdict_del(options, "path");
     qdict_del(options, "host_key_check");
 
-    g_free(hostport);
     return 0;
 
  err:
@@ -600,7 +606,6 @@ static int connect_to_ssh(BDRVSSHState *s, QDict *options,
         libssh2_session_free(s->session);
     }
     s->session = NULL;
-    g_free(hostport);
 
     return ret;
 }
@@ -953,6 +958,68 @@ static coroutine_fn int ssh_co_writev(BlockDriverState *bs,
     return ret;
 }
 
+static void unsafe_flush_warning(BDRVSSHState *s, const char *what)
+{
+    if (!s->unsafe_flush_warning) {
+        error_report("warning: ssh server %s does not support fsync",
+                     s->hostport);
+        if (what) {
+            error_report("to support fsync, you need %s", what);
+        }
+        s->unsafe_flush_warning = true;
+    }
+}
+
+#ifdef HAS_LIBSSH2_SFTP_FSYNC
+
+static coroutine_fn int ssh_flush(BDRVSSHState *s)
+{
+    int r;
+
+    DPRINTF("fsync");
+ again:
+    r = libssh2_sftp_fsync(s->sftp_handle);
+    if (r == LIBSSH2_ERROR_EAGAIN || r == LIBSSH2_ERROR_TIMEOUT) {
+        co_yield(s);
+        goto again;
+    }
+    if (r == LIBSSH2_ERROR_SFTP_PROTOCOL &&
+        libssh2_sftp_last_error(s->sftp) == LIBSSH2_FX_OP_UNSUPPORTED) {
+        unsafe_flush_warning(s, "OpenSSH >= 6.3");
+        return 0;
+    }
+    if (r < 0) {
+        sftp_error_report(s, "fsync failed");
+        return -EIO;
+    }
+
+    return 0;
+}
+
+static coroutine_fn int ssh_co_flush(BlockDriverState *bs)
+{
+    BDRVSSHState *s = bs->opaque;
+    int ret;
+
+    qemu_co_mutex_lock(&s->lock);
+    ret = ssh_flush(s);
+    qemu_co_mutex_unlock(&s->lock);
+
+    return ret;
+}
+
+#else /* !HAS_LIBSSH2_SFTP_FSYNC */
+
+static coroutine_fn int ssh_co_flush(BlockDriverState *bs)
+{
+    BDRVSSHState *s = bs->opaque;
+
+    unsafe_flush_warning(s, "libssh2 >= 1.4.4");
+    return 0;
+}
+
+#endif /* !HAS_LIBSSH2_SFTP_FSYNC */
+
 static int64_t ssh_getlength(BlockDriverState *bs)
 {
     BDRVSSHState *s = bs->opaque;
@@ -976,6 +1043,7 @@ static BlockDriver bdrv_ssh = {
     .bdrv_co_readv                = ssh_co_readv,
     .bdrv_co_writev               = ssh_co_writev,
     .bdrv_getlength               = ssh_getlength,
+    .bdrv_co_flush_to_disk        = ssh_co_flush,
     .create_options               = ssh_create_options,
 };
 
diff --git a/configure b/configure
index 4dd65b0..fa79588 100755
--- a/configure
+++ b/configure
@@ -2357,6 +2357,31 @@ EOF
 fi
 
 ##########################################
+# libssh2_sftp_fsync probe
+
+if test "$libssh2" = "yes"; then
+  cat > $TMPC <<EOF
+#include <stdio.h>
+#include <libssh2.h>
+#include <libssh2_sftp.h>
+int main(void) {
+    LIBSSH2_SESSION *session;
+    LIBSSH2_SFTP *sftp;
+    LIBSSH2_SFTP_HANDLE *sftp_handle;
+    session = libssh2_session_init ();
+    sftp = libssh2_sftp_init (session);
+    sftp_handle = libssh2_sftp_open (sftp, "/", 0, 0);
+    libssh2_sftp_fsync (sftp_handle);
+    return 0;
+}
+EOF
+  # libssh2_cflags/libssh2_libs defined in previous test.
+  if compile_prog "$libssh2_cflags" "$libssh2_libs" ; then
+    QEMU_CFLAGS="-DHAS_LIBSSH2_SFTP_FSYNC $QEMU_CFLAGS"
+  fi
+fi
+
+##########################################
 # linux-aio probe
 
 if test "$linux_aio" != "no" ; then
diff --git a/qemu-doc.texi b/qemu-doc.texi
index 5b36004..dfea4d3 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -1081,11 +1081,16 @@ tools only use MD5 to print fingerprints).
 Currently authentication must be done using ssh-agent.  Other
 authentication methods may be supported in future.
 
-Note: The ssh driver does not obey disk flush requests (ie. to commit
-data to the backing disk when the guest requests it).  This is because
-the underlying protocol (SFTP) does not support this.  Thus there is a
-risk of guest disk corruption if the remote server or network goes
-down during writes.
+Note: Many ssh servers do not support an @code{fsync}-style operation.
+The ssh driver cannot guarantee that disk flush requests are
+obeyed, and this causes a risk of disk corruption if the remote
+server or network goes down during writes.  The driver will
+print a warning when @code{fsync} is not supported:
+
+warning: ssh server @code{ssh.example.com:22} does not support fsync
+
+With sufficiently new versions of libssh2 and OpenSSH, @code{fsync} is
+supported.
 
 @node pcsys_network
 @section Network emulation
-- 
1.8.1.4

[Qemu-devel] [PATCH v9 3/3] iotests: Add 'check -ssh' option to test Secure Shell block device.

[Richard W.M. Jones]

From: "Richard W.M. Jones" <rjones@redhat.com>

Note in order to run these tests on ssh, you must be running a local
ssh daemon, and that daemon must accept loopback connections, and
ssh-agent has to be set up to allow logins on the local daemon.  In
other words, the following command should just work without demanding
any passphrase:

 ssh localhost

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
 tests/qemu-iotests/common    | 5 +++++
 tests/qemu-iotests/common.rc | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/tests/qemu-iotests/common b/tests/qemu-iotests/common
index b3aad89..6826ea7 100644
--- a/tests/qemu-iotests/common
+++ b/tests/qemu-iotests/common
@@ -137,6 +137,7 @@ check options
     -rbd                test rbd
     -sheepdog           test sheepdog
     -nbd                test nbd
+    -ssh                test ssh
     -xdiff		graphical mode diff
     -nocache		use O_DIRECT on backing file
     -misalign		misalign memory allocations
@@ -206,6 +207,10 @@ testlist options
 	    IMGPROTO=nbd
 	    xpand=false
 	    ;;
+        -ssh)
+            IMGPROTO=ssh
+            xpand=false
+            ;;
 	-nocache)
 	    QEMU_IO_OPTIONS="$QEMU_IO_OPTIONS --nocache"
 	    xpand=false
diff --git a/tests/qemu-iotests/common.rc b/tests/qemu-iotests/common.rc
index e522d61..a536bf7 100644
--- a/tests/qemu-iotests/common.rc
+++ b/tests/qemu-iotests/common.rc
@@ -52,6 +52,9 @@ if [ "$IMGPROTO" = "file" ]; then
 elif [ "$IMGPROTO" = "nbd" ]; then
     TEST_IMG_FILE=$TEST_DIR/t.$IMGFMT
     TEST_IMG="nbd:127.0.0.1:10810"
+elif [ "$IMGPROTO" = "ssh" ]; then
+    TEST_IMG_FILE=$TEST_DIR/t.$IMGFMT
+    TEST_IMG="ssh://127.0.0.1$TEST_IMG_FILE"
 else
     TEST_IMG=$IMGPROTO:$TEST_DIR/t.$IMGFMT
 fi
-- 
1.8.1.4

Re: [Qemu-devel] [PATCH v9 1/3] block: Add support for Secure Shell (ssh) block device.

[Stefan Hajnoczi]

On Tue, Apr 09, 2013 at 03:30:52PM +0100, Richard W.M. Jones wrote:
> Changes since v8:
> 
> - Implement the suggestions of Stefan Hajnoczi.
> 
> - Add host_key_check parameter, which you can use like this:
> 
>   ssh://[...]?host_key_check=no     # skip the check entirely
>   ssh://[...]?host_key_check=yes    # the default, uses known_hosts
> 
>   # or check for a specific host key fingerprint:
>   ssh://[...]?host_key_check=md5:<usual SSH host key fingerprint>
>   ssh://[...]?host_key_check=sha1:<SHA1 fingerprint>
> 
> Note that I cannot persuade OpenSSH to display the SHA1 fingerprint of
> a host key, so sha1: is not tested.
> 
> A possible extension to this would be to check for the exact key (not
> the fingerprint, which is just a hash of the key), although in this
> case the URI would be very long indeed, possibly longer than URIs are
> supposed to be in some cases.
> 
> Rich.

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

libssh2.git now includes fsync support so we can take the fsync patch.

Stefan

Re: [Qemu-devel] [PATCH v9 1/3] block: Add support for Secure Shell (ssh) block device.

[Richard W.M. Jones]

Thanks.

I've also developed patches to incorporate this feature into libvirt
and libguestfs.  Here are the latest versions of these:

https://www.redhat.com/archives/libvir-list/2013-April/thread.html#00803
https://www.redhat.com/archives/libguestfs/2013-April/thread.html#00021

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v