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docs: Document share-rw property more thoroughly

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Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Fam Zheng 2018-02-09 13:29:15 +08:00 committed by Kevin Wolf
parent a7e326df1c
commit c1a4b6f924
1 changed files with 10 additions and 0 deletions
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10
docs/qemu-block-drivers.texi
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@ -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