diff options
| -rw-r--r-- | qemu-deprecated.texi | 33 | ||||
| -rw-r--r-- | qemu-nbd.c | 2 | ||||
| -rw-r--r-- | qemu-nbd.texi | 6 |
3 files changed, 39 insertions, 2 deletions
diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi index 9cc20b365c..8a6174df0c 100644 --- a/qemu-deprecated.texi +++ b/qemu-deprecated.texi @@ -160,3 +160,36 @@ Example of legacy encoding: The above, converted to the current supported format: @code{json:@{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"@}} + +@section Related binaries + +@subsection qemu-nbd --partition (since 4.0.0) + +The ``qemu-nbd --partition $digit'' code (also spelled @option{-P}) +can only handle MBR partitions, and has never correctly handled +logical partitions beyond partition 5. If you know the offset and +length of the partition (perhaps by using @code{sfdisk} within the +guest), you can achieve the effect of exporting just that subset of +the disk by use of the @option{--image-opts} option with a raw +blockdev using the @code{offset} and @code{size} parameters layered on +top of any other existing blockdev. For example, if partition 1 is +100MiB long starting at 1MiB, the old command: + +@code{qemu-nbd -t -P 1 -f qcow2 file.qcow2} + +can be rewritten as: + +@code{qemu-nbd -t --image-opts driver=raw,offset=1M,size=100M,file.driver=qcow2,file.backing.driver=file,file.backing.filename=file.qcow2} + +Alternatively, the @code{nbdkit} project provides a more powerful +partition filter on top of its nbd plugin, which can be used to select +an arbitrary MBR or GPT partition on top of any other full-image NBD +export. Using this to rewrite the above example results in: + +@code{qemu-nbd -t -k /tmp/sock -f qcow2 file.qcow2 &} +@code{nbdkit -f --filter=partition nbd socket=/tmp/sock partition=1} + +Note that if you are exposing the export via /dev/nbd0, it is easier +to just export the entire image and then mount only /dev/nbd0p1 than +it is to reinvoke @command{qemu-nbd -c /dev/nbd0} limited to just a +subset of the image. diff --git a/qemu-nbd.c b/qemu-nbd.c index 1f7b2a03f5..00c07fd27e 100644 --- a/qemu-nbd.c +++ b/qemu-nbd.c @@ -787,6 +787,8 @@ int main(int argc, char **argv) flags &= ~BDRV_O_RDWR; break; case 'P': + warn_report("The '-P' option is deprecated; use --image-opts with " + "a raw device wrapper for subset exports instead"); if (qemu_strtoi(optarg, NULL, 0, &partition) < 0 || partition < 1 || partition > 8) { error_report("Invalid partition '%s'", optarg); diff --git a/qemu-nbd.texi b/qemu-nbd.texi index 386bece468..d0c5182814 100644 --- a/qemu-nbd.texi +++ b/qemu-nbd.texi @@ -56,8 +56,10 @@ auto-detecting. @item -r, --read-only Export the disk as read-only. @item -P, --partition=@var{num} -Only expose MBR partition @var{num}. Understands physical partitions -1-4 and logical partitions 5-8. +Deprecated: Only expose MBR partition @var{num}. Understands physical +partitions 1-4 and logical partition 5. New code should instead use +@option{--image-opts} with the raw driver wrapping a subset of the +original image. @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 |