Document some useful qemu-nbd command lines. Mention some restrictions
on particular options, like -p being only for MBR images, or -c/-d
being Linux-only. Update some text given the recent change to no
longer serve oldstyle protocol (missed in commit 7f7dfe2a). Also,
consistently use trailing '.' in describing options.
Signed-off-by: Eric Blake <ebl...@redhat.com>
---
v2: new patch
---
qemu-nbd.texi | 85 +++++++++++++++++++++++++++++++++++++++------------
1 file changed, 66 insertions(+), 19 deletions(-)
diff --git a/qemu-nbd.texi b/qemu-nbd.texi
index 9a84e81eed9..0e24c2801ee 100644
--- a/qemu-nbd.texi
+++ b/qemu-nbd.texi
@@ -8,7 +8,10 @@
@c man begin DESCRIPTION
-Export a QEMU disk image using the NBD protocol.
+Provide access to various QEMU NBD features. Most commonly used to
+export a QEMU disk image using the NBD protocol as a server, but can
+also be used (on Linux) to manage kernel bindings of a /dev/nbdX
+block device to a QEMU server.
@c man end
@@ -27,28 +30,29 @@ supported. The common object types that it makes sense to
define are the
keys, and the @code{tls-creds} object, which is used to supply TLS
credentials for the qemu-nbd server.
@item -p, --port=@var{port}
-The TCP port to listen on (default @samp{10809})
+The TCP port to listen on (default @samp{10809}).
@item -o, --offset=@var{offset}
-The offset into the image
+The offset into the image.
@item -b, --bind=@var{iface}
-The interface to bind to (default @samp{0.0.0.0})
+The interface to bind to (default @samp{0.0.0.0}).
@item -k, --socket=@var{path}
-Use a unix socket with path @var{path}
+Use a unix socket with path @var{path}.
@item --image-opts
Treat @var{filename} as a set of image options, instead of a plain
filename. If this flag is specified, the @var{-f} flag should
not be used, instead the '@code{format=}' option should be set.
@item -f, --format=@var{fmt}
Force the use of the block driver for format @var{fmt} instead of
-auto-detecting
+auto-detecting.
@item -r, --read-only
-Export the disk as read-only
+Export the disk as read-only.
@item -P, --partition=@var{num}
-Only expose partition @var{num}
+Only expose MBR partition @var{num}. Understands physical partitions
+1-4 and logical partitions 5-8.
@item -s, --snapshot
Use @var{filename} as an external snapshot, create a temporary
file with backing_file=@var{filename}, redirect the write to
-the temporary one
+the temporary one.
@item -l, --load-snapshot=@var{snapshot_param}
Load an internal snapshot inside @var{filename} and export it
as an read-only device, @var{snapshot_param} format is
@@ -72,19 +76,18 @@ driver-specific optimized zero write commands.
@var{detect-zeroes} is one of
converts a zero write to an unmap operation and can only be used if
@var{discard} is set to @samp{unmap}. The default is @samp{off}.
@item -c, --connect=@var{dev}
-Connect @var{filename} to NBD device @var{dev}
+Connect @var{filename} to NBD device @var{dev} (Linux only).
@item -d, --disconnect
-Disconnect the device @var{dev}
+Disconnect the device @var{dev} (Linux only).
@item -e, --shared=@var{num}
-Allow up to @var{num} clients to share the device (default @samp{1})
+Allow up to @var{num} clients to share the device (default @samp{1}).
@item -t, --persistent
-Don't exit on the last connection
+Don't exit on the last connection.
@item -x, --export-name=@var{name}
-Set the NBD volume export name. This switches the server to use
-the new style NBD protocol negotiation
+Set the NBD volume export name (default of a zero-length string).
@item -D, --description=@var{description}
Set the NBD volume export description, as a human-readable
-string. Requires the use of @option{-x}
+string.
@item --tls-creds=ID
Enable mandatory TLS encryption for the server by setting the ID
of the TLS credentials object previously created with the --object
@@ -92,11 +95,11 @@ option.
@item --fork
Fork off the server process and exit the parent once the server is running.
@item -v, --verbose
-Display extra debugging information
+Display extra debugging information.
@item -h, --help
-Display this help and exit
+Display this help and exit.
@item -V, --version
-Display version information and exit
+Display version information and exit.
@item -T, --trace
[[enable=]@var{pattern}][,events=@var{file}][,file=@var{file}]
@findex --trace
@include qemu-option-trace.texi
@@ -104,6 +107,50 @@ Display version information and exit
@c man end
+@c man begin EXAMPLES
+Start a server listening on port 10809 that exposes only the
+guest-visible contents of a qcow2 file, with no TLS encryption, and
+with the default export name (an empty string). The command will block
+until the first successful client disconnects:
+
+@example
+qemu-nbd -f qcow2 file.qcow2
+@end example
+
+Start a server listening with encryption on port 10810, and require
+the client to have a correct X.509 certificate to connect to a 1
+megabyte subset of a raw file, using the export name 'subset':
+
+@example
+qemu-nbd \
+ --object tls-creds-x509,id=tls0,endpoint=server,dir=/path/to/qemutls \
+ --tls-creds tls0 -x subset -p 10810 \
+ --image-opts
driver=raw,offset=1M,length=1M,file.driver=file,file.filename=file.raw
+@end example
+
+Serve a read-only copy of just the first MBR partition of a guest
+image over a Unix socket with as many as 5 simultaneous readers, with
+a persistent process forked as a daemon:
+
+@example
+qemu-nbd --fork -t -e 5 -s /path/to/sock -p 1 -r -f qcow2 file.qcow2
+@end example
+
+Expose the guest-visible contents of a qcow2 file via a block device
+/dev/nbd0 (and possibly creating /dev/nbd0p1 and friends for
+partitions found within), then disconnect the device when done.
+@emph{CAUTION}: Do not use this method to mount filesystems from an
+untrusted guest image - a malicious guest may have prepared the image
+to attempt to trigger kernel bugs in partition probing or file system
+mounting.
+
+@example
+qemu-nbd -c /dev/nbd0 -f qcow2 file.qcow2
+qemu-nbd -d /dev/nbd0
+@end example
+
+@c man end
+
@ignore
@setfilename qemu-nbd
--
2.17.2
