| Message ID | 20171123135906.12852-2-famz@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | docs: Add documentation for image locking | expand |
Hello, Am 23.11.2017 um 14:59 schrieb Fam Zheng: > 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 ... > +To check if image locking is active, check the output of "lslocks" command on > +host and see if there are locks held by QEMU process on the image file. More > +than one bytes could be locked by a QEMU instance, each byte of which reflects "one byte", without the 's'? > +a perticular permission that are acquired or protected by the running block "particular", 'e' -> 'a' Philipp
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 <famz@redhat.com> > --- > 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
On Thu, 11/23 18:01, Kevin Wolf wrote: > 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 <famz@redhat.com> > > --- > > 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 Updating all of them. Thanks! Fam
On Thu, 11/23 17:07, Philipp Hahn wrote: > Hello, > > Am 23.11.2017 um 14:59 schrieb Fam Zheng: > > 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 > ... > > +To check if image locking is active, check the output of "lslocks" command on > > +host and see if there are locks held by QEMU process on the image file. More > > +than one bytes could be locked by a QEMU instance, each byte of which reflects > > "one byte", without the 's'? > > > +a perticular permission that are acquired or protected by the running block > > "particular", 'e' -> 'a' > Yes to both. Thanks! Fam
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 +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 +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 +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 +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 +host and see if there are locks held by QEMU process on the image file. More +than one bytes could be locked by a QEMU instance, each byte of which reflects +a perticular permission that are acquired or protected by the running block +driver. + @c man end @ignore diff --git a/qemu-doc.texi b/qemu-doc.texi index 617254917d..db2351c746 100644 --- a/qemu-doc.texi +++ b/qemu-doc.texi @@ -405,6 +405,7 @@ encrypted disk images. * disk_images_iscsi:: iSCSI LUNs * disk_images_gluster:: GlusterFS disk images * disk_images_ssh:: Secure Shell (ssh) disk images +* disk_image_locking:: Disk image file locking @end menu @node disk_images_quickstart
This documents the image locking feature and explains when and how related options can be used. Signed-off-by: Fam Zheng <famz@redhat.com> --- docs/qemu-block-drivers.texi | 36 ++++++++++++++++++++++++++++++++++++ qemu-doc.texi | 1 + 2 files changed, 37 insertions(+)