From c1a4b6f9246bf2841b14b11d4c5a029429f0659a Mon Sep 17 00:00:00 2001 From: Fam Zheng Date: Fri, 9 Feb 2018 13:29:15 +0800 Subject: docs: Document share-rw property more thoroughly Suggested-by: Stefan Hajnoczi Signed-off-by: Fam Zheng Reviewed-by: Stefan Hajnoczi Reviewed-by: Kashyap Chamarthy Signed-off-by: Kevin Wolf --- docs/qemu-block-drivers.texi | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'docs') diff --git a/docs/qemu-block-drivers.texi b/docs/qemu-block-drivers.texi index cd74767ed3..f1793692bb 100644 --- a/docs/qemu-block-drivers.texi +++ b/docs/qemu-block-drivers.texi @@ -845,6 +845,16 @@ QEMU transparently handles lock handover during shared storage migration. For shared virtual disk images between multiple VMs, the "share-rw" device option should be used. +By default, the guest has exclusive write access to its disk image. If the +guest can safely share the disk image with other writers the @code{-device +...,share-rw=on} parameter can be used. This is only safe if the guest is +running software, such as a cluster file system, that coordinates disk accesses +to avoid corruption. + +Note that share-rw=on only declares the guest's ability to share the disk. +Some QEMU features, such as image file formats, require exclusive write access +to the disk image and this is unaffected by the share-rw=on option. + Alternatively, locking can be fully disabled by "locking=off" block device option. In the command line, the option is usually in the form of "file.locking=off" as the protocol driver is normally placed as a "file" child -- cgit v1.2.1