[libvirt] [PATCH] util: mdev: support persistent devices with mdevctl
When a host is rebooted, mediated devices disappear from sysfs. mdevctl (https://github.com/mdevctl/mdevctl) is a utility for managing and persisting these devices. It maintains a registry of mediated devices and can start and stop them by UUID. when libvirt attempts to create a new mediated device object, we currently fail if the path does not exist in sysfs. This patch tries a little bit harder by using mdevctl to attempt to activate the device. The approach is fairly naive -- it just calls 'mdevctl start -u $UUID' without checking whether this UUID is registered with mdevctl or not. See https://bugzilla.redhat.com/show_bug.cgi?id=1699274 Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- NOTES: - an argument could be made that we should simply do nothing here. mdevctl does have support for automatically activating the mediated device when the parent device becomes available (via udev). So if the administrator set up the mdev to start automatically, this patch should not even be necessary. That said, I think this patch could still be useful. - As I said above, the approach is pretty naive. I could have checked whether the device was defined in mdevctl's registry and given a different error message ("try registering this device with mdevctl") in that scenario. But I chose to keep it simple. src/util/virmdev.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/src/util/virmdev.c b/src/util/virmdev.c index 3d5488cdae..7a2f0adedc 100644 --- a/src/util/virmdev.c +++ b/src/util/virmdev.c @@ -25,6 +25,7 @@ #include "virfile.h" #include "virstring.h" #include "viralloc.h" +#include "vircommand.h" #define VIR_FROM_THIS VIR_FROM_NONE @@ -148,9 +149,24 @@ virMediatedDeviceNew(const char *uuidstr, virMediatedDeviceModelType model) return NULL; if (!virFileExists(sysfspath)) { - virReportError(VIR_ERR_DEVICE_MISSING, - _("mediated device '%s' not found"), uuidstr); - return NULL; + bool activated = false; + /* if the mdev device path doesn't exist, we may still be able to start + * the device using mdevctl + */ + char *mdevctl = virFindFileInPath("mdevctl"); + if (mdevctl) { + const char *runargs[] = { mdevctl, "start", "-u", uuidstr, NULL }; + if (virRun(runargs, NULL) == 0) { + /* check to see if it the device exists now */ + activated = virFileExists(sysfspath); + } + } + + if (!activated) { + virReportError(VIR_ERR_DEVICE_MISSING, + _("mediated device '%s' not found"), uuidstr); + return NULL; + } } if (VIR_ALLOC(dev) < 0) -- 2.21.0
On Wed, Aug 14, 2019 at 12:03 AM Jonathon Jongsma <jjongsma@redhat.com> wrote:
When a host is rebooted, mediated devices disappear from sysfs. mdevctl (https://github.com/mdevctl/mdevctl) is a utility for managing and persisting these devices. It maintains a registry of mediated devices and can start and stop them by UUID.
when libvirt attempts to create a new mediated device object, we currently fail if the path does not exist in sysfs. This patch tries a little bit harder by using mdevctl to attempt to activate the device. The approach is fairly naive -- it just calls 'mdevctl start -u $UUID' without checking whether this UUID is registered with mdevctl or not.
See https://bugzilla.redhat.com/show_bug.cgi?id=1699274
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- NOTES: - an argument could be made that we should simply do nothing here. mdevctl does have support for automatically activating the mediated device when the parent device becomes available (via udev). So if the administrator set up the mdev to start automatically, this patch should not even be necessary. That said, I think this patch could still be useful. - As I said above, the approach is pretty naive. I could have checked whether the device was defined in mdevctl's registry and given a different error message ("try registering this device with mdevctl") in that scenario. But I chose to keep it simple.
So, I've noticed that mdevctl is not on Fedora yet, at least according to: https://bugzilla.redhat.com/show_bug.cgi?id=1728381 In any case, would you mind to also update the spec file and add something like: `Recommends: mdevctl`? Recommends is a weak dependency. It shouldn't force mdevctl to be installed, but suggests it to be installed. Best Regards, -- Fabiano Fidêncio
On 8/14/19 12:02 AM, Jonathon Jongsma wrote:
When a host is rebooted, mediated devices disappear from sysfs. mdevctl (https://github.com/mdevctl/mdevctl) is a utility for managing and persisting these devices. It maintains a registry of mediated devices and can start and stop them by UUID.
when libvirt attempts to create a new mediated device object, we currently fail if the path does not exist in sysfs. This patch tries a little bit harder by using mdevctl to attempt to activate the device. The approach is fairly naive -- it just calls 'mdevctl start -u $UUID' without checking whether this UUID is registered with mdevctl or not.
See https://bugzilla.redhat.com/show_bug.cgi?id=1699274
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- NOTES: - an argument could be made that we should simply do nothing here. mdevctl does have support for automatically activating the mediated device when the parent device becomes available (via udev). So if the administrator set up the mdev to start automatically, this patch should not even be necessary. That said, I think this patch could still be useful.
I would actually like to use this argument since this patch unconditionally starts/creates a persistently defined mdev without ever stopping/destroying it and also not looking if it is defined as to be automatically started or manually started. If the mdev is specified in mdevctl to be started automatically I would rate this as mdevctl is in control of this mdevs lifecycle and libvirt should not interfere with it. It might be that I am over-interpreting auto and manual as start options in mdevctl but it feels to me that libvirt and mdevctl should not run into a management clash of host resources. In addition what about a user specifiable tag in the domain xmls mdev definition which controls the management behavior of an mdev with mdevctl or another tool?
- As I said above, the approach is pretty naive. I could have checked whether the device was defined in mdevctl's registry and given a different error message ("try registering this device with mdevctl") in that scenario. But I chose to keep it simple.
src/util/virmdev.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/src/util/virmdev.c b/src/util/virmdev.c index 3d5488cdae..7a2f0adedc 100644 --- a/src/util/virmdev.c +++ b/src/util/virmdev.c @@ -25,6 +25,7 @@ #include "virfile.h" #include "virstring.h" #include "viralloc.h" +#include "vircommand.h"
#define VIR_FROM_THIS VIR_FROM_NONE
@@ -148,9 +149,24 @@ virMediatedDeviceNew(const char *uuidstr, virMediatedDeviceModelType model) return NULL;
if (!virFileExists(sysfspath)) { - virReportError(VIR_ERR_DEVICE_MISSING, - _("mediated device '%s' not found"), uuidstr); - return NULL; + bool activated = false; + /* if the mdev device path doesn't exist, we may still be able to start + * the device using mdevctl + */ + char *mdevctl = virFindFileInPath("mdevctl"); + if (mdevctl) { + const char *runargs[] = { mdevctl, "start", "-u", uuidstr, NULL }; + if (virRun(runargs, NULL) == 0) { + /* check to see if it the device exists now */ + activated = virFileExists(sysfspath); + } + } + + if (!activated) { + virReportError(VIR_ERR_DEVICE_MISSING, + _("mediated device '%s' not found"), uuidstr); + return NULL; + } }
if (VIR_ALLOC(dev) < 0)
-- Mit freundlichen Grüßen/Kind regards Boris Fiuczynski IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Matthias Hartmann Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen Registergericht: Amtsgericht Stuttgart, HRB 243294
On Wed, 2019-08-14 at 16:14 +0200, Boris Fiuczynski wrote:
On 8/14/19 12:02 AM, Jonathon Jongsma wrote:
When a host is rebooted, mediated devices disappear from sysfs. mdevctl (https://github.com/mdevctl/mdevctl) is a utility for managing and persisting these devices. It maintains a registry of mediated devices and can start and stop them by UUID.
when libvirt attempts to create a new mediated device object, we currently fail if the path does not exist in sysfs. This patch tries a little bit harder by using mdevctl to attempt to activate the device. The approach is fairly naive -- it just calls 'mdevctl start -u $UUID' without checking whether this UUID is registered with mdevctl or not.
See https://bugzilla.redhat.com/show_bug.cgi?id=1699274
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- NOTES: - an argument could be made that we should simply do nothing here. mdevctl does have support for automatically activating the mediated device when the parent device becomes available (via udev). So if the administrator set up the mdev to start automatically, this patch should not even be necessary. That said, I think this patch could still be useful.
I would actually like to use this argument since this patch unconditionally starts/creates a persistently defined mdev without ever stopping/destroying it and also not looking if it is defined as to be automatically started or manually started. If the mdev is specified in mdevctl to be started automatically I would rate this as mdevctl is in control of this mdevs lifecycle and libvirt should not interfere with it. It might be that I am over-interpreting auto and manual as start options in mdevctl but it feels to me that libvirt and mdevctl should not run into a management clash of host resources.
In addition what about a user specifiable tag in the domain xmls mdev definition which controls the management behavior of an mdev with mdevctl or another tool?
Thanks for the feedback. I welcome additional opinions on this. If there's a concensus that the right approach is to do nothing, I can drop this patch. Or alternately, we could simply point users toward mdevctl in the error message. For example, something like: diff --git a/src/util/virmdev.c b/src/util/virmdev.c index 3d5488cdae..70d990eace 100644 --- a/src/util/virmdev.c +++ b/src/util/virmdev.c @@ -149,7 +149,7 @@ virMediatedDeviceNew(const char *uuidstr, virMediatedDeviceModelType model) if (!virFileExists(sysfspath)) { virReportError(VIR_ERR_DEVICE_MISSING, - _("mediated device '%s' not found"), uuidstr); + _("mediated device '%s' not found. Persistent devices can be managed with 'mdevctl'."), uuidstr); return NULL; }
- As I said above, the approach is pretty naive. I could have checked whether the device was defined in mdevctl's registry and given a different error message ("try registering this device with mdevctl") in that scenario. But I chose to keep it simple.
src/util/virmdev.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/src/util/virmdev.c b/src/util/virmdev.c index 3d5488cdae..7a2f0adedc 100644 --- a/src/util/virmdev.c +++ b/src/util/virmdev.c @@ -25,6 +25,7 @@ #include "virfile.h" #include "virstring.h" #include "viralloc.h" +#include "vircommand.h"
#define VIR_FROM_THIS VIR_FROM_NONE
@@ -148,9 +149,24 @@ virMediatedDeviceNew(const char *uuidstr, virMediatedDeviceModelType model) return NULL;
if (!virFileExists(sysfspath)) { - virReportError(VIR_ERR_DEVICE_MISSING, - _("mediated device '%s' not found"), uuidstr); - return NULL; + bool activated = false; + /* if the mdev device path doesn't exist, we may still be able to start + * the device using mdevctl + */ + char *mdevctl = virFindFileInPath("mdevctl"); + if (mdevctl) { + const char *runargs[] = { mdevctl, "start", "-u", uuidstr, NULL }; + if (virRun(runargs, NULL) == 0) { + /* check to see if it the device exists now */ + activated = virFileExists(sysfspath); + } + } + + if (!activated) { + virReportError(VIR_ERR_DEVICE_MISSING, + _("mediated device '%s' not found"), uuidstr); + return NULL; + } }
if (VIR_ALLOC(dev) < 0)
On 8/19/19 4:48 PM, Jonathon Jongsma wrote:
On Wed, 2019-08-14 at 16:14 +0200, Boris Fiuczynski wrote:
On 8/14/19 12:02 AM, Jonathon Jongsma wrote:
When a host is rebooted, mediated devices disappear from sysfs. mdevctl (https://github.com/mdevctl/mdevctl) is a utility for managing and persisting these devices. It maintains a registry of mediated devices and can start and stop them by UUID.
when libvirt attempts to create a new mediated device object, we currently fail if the path does not exist in sysfs. This patch tries a little bit harder by using mdevctl to attempt to activate the device. The approach is fairly naive -- it just calls 'mdevctl start -u $UUID' without checking whether this UUID is registered with mdevctl or not.
See https://bugzilla.redhat.com/show_bug.cgi?id=1699274
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- NOTES: - an argument could be made that we should simply do nothing here. mdevctl does have support for automatically activating the mediated device when the parent device becomes available (via udev). So if the administrator set up the mdev to start automatically, this patch should not even be necessary. That said, I think this patch could still be useful.
I would actually like to use this argument since this patch unconditionally starts/creates a persistently defined mdev without ever stopping/destroying it and also not looking if it is defined as to be automatically started or manually started. If the mdev is specified in mdevctl to be started automatically I would rate this as mdevctl is in control of this mdevs lifecycle and libvirt should not interfere with it. It might be that I am over-interpreting auto and manual as start options in mdevctl but it feels to me that libvirt and mdevctl should not run into a management clash of host resources.
In addition what about a user specifiable tag in the domain xmls mdev definition which controls the management behavior of an mdev with mdevctl or another tool?
Thanks for the feedback. I welcome additional opinions on this. If there's a concensus that the right approach is to do nothing, I can drop this patch. Or alternately, we could simply point users toward mdevctl in the error message. For example, something like:
diff --git a/src/util/virmdev.c b/src/util/virmdev.c index 3d5488cdae..70d990eace 100644 --- a/src/util/virmdev.c +++ b/src/util/virmdev.c @@ -149,7 +149,7 @@ virMediatedDeviceNew(const char *uuidstr, virMediatedDeviceModelType model)
if (!virFileExists(sysfspath)) { virReportError(VIR_ERR_DEVICE_MISSING, - _("mediated device '%s' not found"), uuidstr); + _("mediated device '%s' not found. Persistent devices can be managed with 'mdevctl'."), uuidstr); return NULL; }
Unless there is a request for us to start mdevs, I'd rather see this error message than us trying to do anything because libvirt's already trying to manage more than enough and it's biting us back. Michal
participants (4)
-
Boris Fiuczynski -
Fabiano Fidêncio -
Jonathon Jongsma -
Michal Privoznik