Re: [libvirt] QEMU's File Descriptors

Dear Martin,

Does libvirt currently reopen image files when resuming a VM?

There is an issue of an IO Error after restarting a gluster volume and probably doing other maintenance tasks (VM will not resume) which probably invalidates QEMU's File Descriptors.

It's an old BZ.

Martin Kletzander <mkletzan(a)redhat.com&gt; wrote: >On Tue, Feb 24, 2015 at 09:24:51AM -0500, Stefan Berger wrote: >>On 02/24/2015 08:34 AM, Martin Kletzander wrote: >>>On Mon, Feb 23, 2015 at 06:50:46AM -0500, Stefan Berger wrote: >>>>Implement virCommandPassFDGetFDIndex to determine the index a given >>>>file descriptor will have when passed to the child process. When this >>>>function is called, a flag is set to prevent the reordering of the >>>>file descriptors. >>>> >>>>Signed-off-by: Stefan Berger <stefanb(a)linux.vnet.ibm.com&gt; >>>>--- >>>>src/libvirt_private.syms | 1 + >>>>src/util/vircommand.c | 33 +++++++++++++++++++++++++++++++++ >>>>src/util/vircommand.h | 3 +++ >>>>3 files changed, 37 insertions(+) >>>> >>>>diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms >>>>index c156b40..aadb833 100644 >>>>--- a/src/libvirt_private.syms >>>>+++ b/src/libvirt_private.syms >>>>@@ -1213,6 +1213,7 @@ virCommandNewArgList; >>>>virCommandNewArgs; >>>>virCommandNonblockingFDs; >>>>virCommandPassFD; >>>>+virCommandPassFDGetFDIndex; >>>>virCommandPassListenFDs; >>>>virCommandRawStatus; >>>>virCommandRequireHandshake; >>>>diff --git a/src/util/vircommand.c b/src/util/vircommand.c >>>>index 6527d85..2616446 100644 >>>>--- a/src/util/vircommand.c >>>>+++ b/src/util/vircommand.c >>>>@@ -67,6 +67,7 @@ enum { >>>> VIR_EXEC_RUN_SYNC = (1 << 3), >>>> VIR_EXEC_ASYNC_IO = (1 << 4), >>>> VIR_EXEC_LISTEN_FDS = (1 << 5), >>>>+ VIR_EXEC_FIXED_FDS = (1 << 6), >>> >>>The descriptors shouldn't get reordered *unless* there is >>>VIR_EXEC_LISTEN_FDS flag added, so FIXED_FDS shouldn't be necessary. >>>Or is there a bug in that approach that needs fixing? >> >>Hm, it depends on the order in which APIs are called where we either >>need to protect against re-ordering (if we use indices) or we cannot >>allow indices to be used if we need to reorder them. So, actually the >>way the patch is, it isn't correct, either. >> >>The problem of having to prevent the reordering of file descriptors >>when we are building the QEMU command line with file descriptors >>already exists today. So maybe I could just remove this flag and the >>related check knowing that reordering of file descriptors and building >>the QEMU command line that contains file descriptor (from before the >>order) would not be allowed today without any of the patches I am >>trying to add. >> > >You surely and safely can. The point behind reordering FDs was that >when you're using FD passing as done by systemd, those FDs passed must >start from number 3. However, because we are already passing a bunch >of file descriptors to QEMU and other commands, we *must not* reorder >any file descriptors because it wouldn't work, of course. > >Martin > >-- >libvir-list mailing list &gt;libvir-list(a)redhat.com >https://www.redhat.com/mailman/listinfo/libvir-list