Merge remote-tracking branch 'remotes/rth/tags/pull-tcg-20190610' into staging

[mirror_qemu.git] / docs / qemu-block-drivers.texi

diff --git a/docs/qemu-block-drivers.texi b/docs/qemu-block-drivers.texi
index cd74767ed39a8efd80bd10728577722f54c86ccc..da06a9bc838d056d6295b0d1c50d5d05d84513f6 100644 (file)
--- a/docs/qemu-block-drivers.texi
+++ b/docs/qemu-block-drivers.texi
@@ -524,7 +524,7 @@ You can create a cloned image from the existing snapshot.
 @example
 qemu-img create -b sheepdog:///@var{base}#@var{tag} sheepdog:///@var{image}
 @end example
-where @var{base} is a image name of the source snapshot and @var{tag}
+where @var{base} is an image name of the source snapshot and @var{tag}
 is its tag name.
 
 You can use an unix socket instead of an inet socket:
@@ -632,7 +632,7 @@ qemu-system-i386 -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \
 @end example
 
 
-Howto set up a simple iSCSI target on loopback and accessing it via QEMU:
+How to set up a simple iSCSI target on loopback and access it via QEMU:
 @example
 This example shows how to set up an iSCSI target with one CDROM and one DISK
 using the Linux STGT software target. This target is available on Red Hat based
@@ -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