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authorRichard W.M. Jones <rjones@redhat.com>2013-04-09 15:30:54 +0100
committerStefan Hajnoczi <stefanha@redhat.com>2013-04-15 10:18:05 +0200
commit9a2d462e7bfba36597ccbd3774ba3bb1bd4c54d8 (patch)
tree99f84f93211231e0fc37909e943779a536189ef5 /qemu-doc.texi
parent0a12ec87a513b31eb3b6e035d30649e483322270 (diff)
block: ssh: Use libssh2_sftp_fsync (if supported by libssh2) to flush to disk.
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 <stefanha@redhat.com>
Diffstat (limited to 'qemu-doc.texi')
-rw-r--r--qemu-doc.texi15
1 files changed, 10 insertions, 5 deletions
diff --git a/qemu-doc.texi b/qemu-doc.texi
index 5b36004873..dfea4d3799 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