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[Qemu-block] [PATCH v4 03/21] qemu-nbd: Enhance man page

From: Eric Blake
Subject: [Qemu-block] [PATCH v4 03/21] qemu-nbd: Enhance man page
Date: Thu, 17 Jan 2019 13:36:40 -0600

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 <address@hidden>
Reviewed-by: Richard W.M. Jones <address@hidden>

v3: wording improvements, use -t in more examples [Rich]
 qemu-nbd.texi | 91 ++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 72 insertions(+), 19 deletions(-)

diff --git a/qemu-nbd.texi b/qemu-nbd.texi
index 96b1546006a..3f22559beb4 100644
--- a/qemu-nbd.texi
+++ b/qemu-nbd.texi
@@ -10,11 +10,17 @@

 Export a QEMU disk image using the NBD protocol.

+Other uses:
+Bind a /dev/nbdX block device to a QEMU server (on Linux).
address@hidden 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, address@hidden
-The TCP port to listen on (default @samp{10809})
+The TCP port to listen on (default @samp{10809}).
 @item -o, address@hidden
-The offset into the image
+The offset into the image.
 @item -b, address@hidden
-The interface to bind to (default @samp{})
+The interface to bind to (default @samp{}).
 @item -k, address@hidden
-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, address@hidden
 Force the use of the block driver for format @var{fmt} instead of
 @item -r, --read-only
-Export the disk as read-only
+Export the disk as read-only.
 @item -P, address@hidden
-Only expose partition @var{num}
+Only expose MBR partition @var{num}.  Understands physical partitions
+1-4 and logical partitions 5-8.
 @item -B, address@hidden
 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 address@hidden, redirect the write to
-the temporary one
+the temporary one.
 @item -l, address@hidden
 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, address@hidden
-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, address@hidden
-Allow up to @var{num} clients to share the device (default @samp{1})
+Allow up to @var{num} clients to share the device (default
address@hidden). 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, address@hidden
-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, address@hidden
 Set the NBD volume export description, as a human-readable
-string. Requires the use of @option{-x}
 @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 address@hidden,address@hidden,address@hidden
 @findex --trace
 @include qemu-option-trace.texi
@@ -108,6 +116,51 @@ Display version information and exit

 @c man end

address@hidden 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
+qemu-nbd -f qcow2 file.qcow2
address@hidden 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':
+qemu-nbd \
+  --object tls-creds-x509,id=tls0,endpoint=server,dir=/path/to/qemutls \
+  --tls-creds tls0 -t -x subset -p 10810 \
+  --image-opts 
address@hidden 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:
+qemu-nbd --fork -t -e 5 -s /path/to/sock -p 1 -r -f qcow2 file.qcow2
address@hidden 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.
address@hidden: 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
+qemu-nbd -c /dev/nbd0 -f qcow2 file.qcow2
+qemu-nbd -d /dev/nbd0
address@hidden example
address@hidden man end

 @setfilename qemu-nbd

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