[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PATCH 09/11] block: ssh: Use libssh2_sftp_fsync (if suppor
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PATCH 09/11] block: ssh: Use libssh2_sftp_fsync (if supported by libssh2) to flush to disk. |
Date: |
Mon, 15 Apr 2013 10:22:42 +0200 |
From: "Richard W.M. Jones" <address@hidden>
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.
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
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 e6c5d2c..a97bf31 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] [PULL 00/11] Block patches, Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PATCH 01/11] block: Introduce bdrv_writev_vmstate, Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PATCH 02/11] savevm: Implement block_writev_buffer(), Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PATCH 03/11] block: Introduce bdrv_pwritev() for qcow2_save_vmstate, Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PATCH 04/11] qemu-iotests: A few more bdrv_pread/pwrite tests, Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PATCH 05/11] qemu-iotests: Add test for -drive options, Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PATCH 07/11] ide: refuse WIN_READ_NATIVE_MAX on empty device, Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PATCH 06/11] qemu-iotests: filter QEMU_PROG in 051.out, Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PATCH 10/11] iotests: Add 'check -ssh' option to test Secure Shell block device., Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PATCH 09/11] block: ssh: Use libssh2_sftp_fsync (if supported by libssh2) to flush to disk.,
Stefan Hajnoczi <=
- [Qemu-devel] [PATCH 08/11] block: Add support for Secure Shell (ssh) block device., Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PATCH 11/11] rbd: add an asynchronous flush, Stefan Hajnoczi, 2013/04/15
- [Qemu-devel] [PULL 00/11] Block patches, Stefan Hajnoczi, 2013/04/26
- [Qemu-devel] [PATCH 01/11] block: Introduce bdrv_writev_vmstate, Stefan Hajnoczi, 2013/04/26
- [Qemu-devel] [PATCH 01/11] block/ssh: Require libssh2 >= 1.2.8., Stefan Hajnoczi, 2013/04/26
- [Qemu-devel] [PATCH 02/11] savevm: Implement block_writev_buffer(), Stefan Hajnoczi, 2013/04/26
- [Qemu-devel] [PATCH 03/11] block: Introduce bdrv_pwritev() for qcow2_save_vmstate, Stefan Hajnoczi, 2013/04/26
- [Qemu-devel] [PATCH 02/11] sheepdog: add discard/trim support for sheepdog, Stefan Hajnoczi, 2013/04/26
- [Qemu-devel] [PATCH 03/11] sheepdog: use BDRV_SECTOR_SIZE, Stefan Hajnoczi, 2013/04/26
- [Qemu-devel] [PATCH 04/11] qemu-iotests: A few more bdrv_pread/pwrite tests, Stefan Hajnoczi, 2013/04/26