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[Qemu-block] [PULL 03/21] qemu-nbd: Enhance man page
From: |
Eric Blake |
Subject: |
[Qemu-block] [PULL 03/21] qemu-nbd: Enhance man page |
Date: |
Mon, 21 Jan 2019 16:48:49 -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>
Message-Id: <address@hidden>
Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
qemu-nbd.texi | 94 ++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 75 insertions(+), 19 deletions(-)
diff --git a/qemu-nbd.texi b/qemu-nbd.texi
index 96b1546006a..f218291bf30 100644
--- a/qemu-nbd.texi
+++ b/qemu-nbd.texi
@@ -10,11 +10,17 @@
Export a QEMU disk image using the NBD protocol.
+Other uses:
address@hidden
address@hidden
+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{0.0.0.0})
+The interface to bind to (default @samp{0.0.0.0}).
@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
-auto-detecting
+auto-detecting.
@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}
+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 address@hidden,address@hidden,address@hidden
@findex --trace
@include qemu-option-trace.texi
@@ -108,6 +116,54 @@ 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
+disconnects:
+
address@hidden
+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':
+
address@hidden
+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
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:
+
address@hidden
+qemu-nbd --fork --persistent --shared=5 --socket=/path/to/sock \
+ --partition=1 --read-only --format=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.
+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.
+
address@hidden
+qemu-nbd -c /dev/nbd0 -f qcow2 file.qcow2
+qemu-nbd -d /dev/nbd0
address@hidden example
+
address@hidden man end
+
@ignore
@setfilename qemu-nbd
--
2.20.1
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