> >>>>> Hi All, > >>>>> > >>>>> I'm having an interesting issue. I am working on a project that > >>>>> requires me to share memory between dom0 and domUs. I have this > >>>>> successfully working using the grant table and the XenStore to > >>>>> communicate grefs. > >>>>> > >>>>> My issue is this. I have one domU running Ubuntu 12.04 with a default > >>>>> 3.8.x kernel that has no issue reading or writing from the XenStore. > >>>>> My work also requires some kernel modifications, and we have made > >>>>> these changes in the 4.1.0 kernel. In particular, we've only added a > >>>>> simple hypercall. This modified kernel is what dom0 is running, on top > >>>>> of Xen 4.7 rc1. > >>>> > >>>> Without reading the rest of the thread but seeing the kernel versions. > >>>> Can you check how you're communicating to xenstore? Is it via > >>>> /dev/xen/xenbus or /proc/xen/xenbus? Anything after 3.14 will give you > >>>> deadlocks if you try to use /proc/xen/xenbus. Xen 4.6 and newer should > >>>> prefer /dev/xen/xenbus. Same thing can happen with privcmd but making > >>>> that default didn't land until Xen 4.7. Since you're on the right > >>>> versions I expect you're using /dev/xen/xenbus but you never know. > >>> > >>> How do I know which is being used? /dev/xen/xenbus is there and so is > >>> process/xen/xenbus. Could this be a problem with header version > >>> mismatches or something similar? I'm using the xen/xenstore.h header > >>> file for all of my xenstore interactions. I'm running Xen 4.7 so it > >>> should be in /dev/, and the old kernel is before 3.14 but the new one > >>> is after, but I would presume the standard headers are updated to > >>> account for this. Is there an easy way to check for this? Also, would > >>> the same issue cause writes to fails? Because writes from the same > >>> domain work fine, and appear to other domains using xenstore-ls. > >>> > >>> Regards, > >>> Dagaen Golomb > >>> > >> > >> Use strace on the process and see what gets opened. > > > > Ah, of course. It seems both the working and non-working domains are > > using /proc/... > > Then according to Doug, "Anything after 3.14 will give you > > deadlocks if you try to use /proc/xen/xenbus.". Maybe the non-working domU uses kernel version after 3.14.
It does, being the custom kernel on version 4.1.0. But Dom0 uses this same exact kernel and reads/writes just fine! The only solution if this is indeed the problem appears to be changing the kernel source we build on or some hacky method such as symlinking /proc/.. to /dev/.., there has to be an elegant real solution to this... Regards, Dagaen Golomb
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