diff options
| -rw-r--r-- | qemu-nbd.texi | 94 |
1 files changed, 75 insertions, 19 deletions
diff --git a/qemu-nbd.texi b/qemu-nbd.texi index 96b1546006..f218291bf3 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 |