From 649cb3fdd8a60caa687452be84fb06de78fead9b Mon Sep 17 00:00:00 2001

From: John Snow <jsnow@redhat.com>

Date: Wed, 27 Mar 2019 17:22:37 +0100

Subject: [PATCH 099/163] qemu-nbd: Enhance man page

RH-Author: John Snow <jsnow@redhat.com>

Message-id: <20190327172308.31077-25-jsnow@redhat.com>

Patchwork-id: 85186

O-Subject: [RHEL-7.7 qemu-kvm-rhev PATCH 24/55] qemu-nbd: Enhance man page

Bugzilla: 1691009

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

RH-Acked-by: Max Reitz <mreitz@redhat.com>

RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>

From: Eric Blake <eblake@redhat.com>

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 <eblake@redhat.com>

Reviewed-by: Richard W.M. Jones <rjones@redhat.com>

Message-Id: <20190117193658.16413-4-eblake@redhat.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

(cherry picked from commit 86b7f6771f0cd1552791d1bfc2bdebd65cf967a3)

Signed-off-by: John Snow <jsnow@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 qemu-nbd.texi | 94 +++++++++++++++++++++++++++++++++++++++++++++++------------

 1 file changed, 75 insertions(+), 19 deletions(-)

diff --git a/qemu-nbd.texi b/qemu-nbd.texi

index 96b1546..f218291 100644

--- a/qemu-nbd.texi

+++ b/qemu-nbd.texi

@@ -10,11 +10,17 @@

 Export a QEMU disk image using the NBD protocol.

+Other uses:

+@itemize

+@item

+Bind a /dev/nbdX block device to a QEMU server (on Linux).

+@end itemize

+

 @c man end

 @c man begin OPTIONS

 @var{filename} is a disk image filename, or a set of block

-driver options if @var{--image-opts} is specified.

+driver options if @option{--image-opts} is specified.

 @var{dev} is an NBD device.

@@ -27,24 +33,25 @@ 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 -B, --bitmap=@var{name}

 If @var{filename} has a qcow2 persistent bitmap @var{name}, expose

 that bitmap via the ``qemu:dirty-bitmap:@var{name}'' context

@@ -52,7 +59,7 @@ accessible through NBD_OPT_SET_META_CONTEXT.

 @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

@@ -76,19 +83,20 @@ 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}). Safe for readers, but for now, consistency is not

+guaranteed between multiple writers.

 @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

@@ -96,11 +104,11 @@ 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

@@ -108,6 +116,54 @@ 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 is

+one-shot, and will block until the first successful client

+disconnects:

+

+@example

+qemu-nbd -f qcow2 file.qcow2

+@end example

+

+Start a long-running server listening with encryption on port 10810,

+and require clients 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 -t -x subset -p 10810 \

+  --image-opts driver=raw,offset=1M,size=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 --persistent --shared=5 --socket=/path/to/sock \

+  --partition=1 --read-only --format=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.

+Access to bind qemu-nbd to an /dev/nbd device generally requires root

+privileges, and may also require the execution of @code{modprobe nbd}

+to enable the kernel NBD client module.  @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

-- 

1.8.3.1