From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46513) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eHusX-0002us-SE for qemu-devel@nongnu.org; Thu, 23 Nov 2017 12:01:38 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eHusT-0004J7-IH for qemu-devel@nongnu.org; Thu, 23 Nov 2017 12:01:33 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34964) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eHusT-0004Im-99 for qemu-devel@nongnu.org; Thu, 23 Nov 2017 12:01:29 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A6B41C05679B for ; Thu, 23 Nov 2017 17:01:27 +0000 (UTC) Date: Thu, 23 Nov 2017 18:01:22 +0100 From: Kevin Wolf Message-ID: <20171123170122.GB4375@localhost.localdomain> References: <20171123135906.12852-1-famz@redhat.com> <20171123135906.12852-2-famz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171123135906.12852-2-famz@redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/2] docs: Add image locking subsection List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: qemu-devel@nongnu.org, mreitz@redhat.com Am 23.11.2017 um 14:59 hat Fam Zheng geschrieben: > This documents the image locking feature and explains when and how > related options can be used. > > Signed-off-by: Fam Zheng > --- > docs/qemu-block-drivers.texi | 36 ++++++++++++++++++++++++++++++++++++ > qemu-doc.texi | 1 + > 2 files changed, 37 insertions(+) > > diff --git a/docs/qemu-block-drivers.texi b/docs/qemu-block-drivers.texi > index 1cb1e55686..fa2e90d15f 100644 > --- a/docs/qemu-block-drivers.texi > +++ b/docs/qemu-block-drivers.texi > @@ -785,6 +785,42 @@ warning: ssh server @code{ssh.example.com:22} does not support fsync > With sufficiently new versions of libssh2 and OpenSSH, @code{fsync} is > supported. > > +@node disk_image_locking > +@subsection Disk image file locking > + > +By default, QEMU tries to protect image files from unexpected concurrent > +access, as long as it's supported by the block protocol driver and host > +operating system. If multiple QEMU processes (including QEMU emulators and > +utilities) try to open the same image with conflicting accessing modes, all but > +the first one will get an error. > + > +This feature is currently supported by the file protocol on Linux with Open s/with/with the/ > +File Descriptor (OFD) locking API, and can be configured to fall back to POSIX > +locking if the POSIX host doesn't support Linux OFD locking. > + > +To explicitly enable image locking, specify "locking=on" in the file protocol > +driver options. If OFD locking is not possible, a warning will be printed and > +the POSIX locking API will be used. In this case there is risk that the lock s/risk/a risk/ (native speakers, is this the right correction?) > +will get silently lost when doing hot plugging and block jobs, due to the > +shortcomings of the POSIX locking API. > + > +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. > + > +Alternatively, locking can be fully disabled by "locking=off" block device s/by/with the/ > +option. In the command line the option is usually in the form of Comma after "command line"? > +"file.locking=off" as the protocol driver is normally placed as a "file" child > +under a format driver. For example: > + > +@code{-blockdev driver=qcow2,file.filename=/path/to/image,file.locking=off,file.driver=file} > + > +To check if image locking is active, check the output of "lslocks" command on _the_ "lslocks" command > +host and see if there are locks held by QEMU process on the image file. More "by a" or "by the", depending on what exactly you want to say > +than one bytes could be locked by a QEMU instance, each byte of which reflects s/bytes/byte/ > +a perticular permission that are acquired or protected by the running block s/are/is/ > +driver. > + > @c man end Kevin