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Re: [libvirt] [RFC] [PATCH v3 2/6] add fuse support for libvirt lxc



On Tue, Sep 11, 2012 at 10:54:48AM +0800, Gao feng wrote:
> this patch addes fuse support for libvirt lxc.
> we can use fuse filesystem to generate sysinfo dynamically,
> So we can isolate /proc/meminfo,cpuinfo and so on through
> fuse filesystem.
> 
> we mount fuse filesystem for every container.the mount name
> is Lxc-containename-fuse,mount point is
> localstatedir/run/libvirt/lxc/containername.
> 
> Signed-off-by: Gao feng <gaofeng cn fujitsu com>

> diff --git a/src/lxc/lxc_controller.c b/src/lxc/lxc_controller.c
> index e5aea11..c5f4951 100644
> --- a/src/lxc/lxc_controller.c
> +++ b/src/lxc/lxc_controller.c
> @@ -1657,6 +1659,14 @@ int main(int argc, char *argv[])
>          }
>      }
>  
> +    rc = virThreadCreate(&thread, true, lxcRegisterFuse,
> +                         (void *)ctrl->def);
> +    if (rc < 0) {
> +        virReportSystemError(-rc, "%s",
> +                             _("Create Fuse filesystem failed"));
> +        goto cleanup;
> +    }
> +

This is the wrong place to start FUSE. At this point the LXC
controller is still sharing its mount namespace with the host
OS. This causes the FUSE mount for each container to become
visible in the host, which is not what we want.

We must only start FUSE, after, we have done the unshare()
call while setting up /dev/pts.


> +void lxcRegisterFuse(void *DomainDef)

More conventional naming would be  'void *opaque'

> +{
> +    int argc = 4;
> +    char *argv[argc];
> +    char *path = NULL;
> +    char *name = NULL;
> +    virDomainDefPtr def = (virDomainDefPtr) DomainDef;
> +
> +    if (virAsprintf(&name, "Lxc-%s-fuse", def->name) < 0) {
> +        virReportOOMError();
> +        goto cleanup;
> +    }
> +
> +    if (virAsprintf(&path, "%s/%s/", LXC_STATE_DIR, def->name) < 0) {
> +        virReportOOMError();
> +        goto cleanup;
> +    }
> +
> +    if (virFileMakePath(path) < 0) {
> +        virReportSystemError(errno, _("Cannot create %s"), path);
> +        goto cleanup;
> +    }
> +
> +    argv[0] = name;
> +    argv[1] = path;
> +    argv[2] = (char *)"-odirect_io";
> +    argv[3] = (char *)"-f";
> +
> +    if (fuse_main(argc, argv, &lxcProcOper, def) < 0)
> +        virReportSystemError(errno, "%s", _("Cannot start fuse"));
> +
> +cleanup:
> +    VIR_FREE(name);
> +    VIR_FREE(path);
> +    return;
> +}
> +
> +void lxcUnregisterFuse(virDomainDefPtr def)
> +{
> +    char *path = NULL;
> +
> +    if (virAsprintf(&path, "%s/%s/", LXC_STATE_DIR, def->name) < 0) {
> +        virReportOOMError();
> +        return;
> +    }
> +
> +    if (umount(path) < 0)
> +         virReportSystemError(errno, "%s",
> +                              _("umount fuse filesystem failed"));
> +
> +    VIR_FREE(path);
> +}
> +
> +#else
> +void lxcRegisterFuse(void *DomainDef ATTRIBUTE_UNUSED)
> +{
> +}
> +
> +void lxcUnregisterFuse(virDomainDefPtr def ATTRIBUTE_UNUSED)
> +{
> +}
> +#endif

> diff --git a/src/lxc/lxc_process.c b/src/lxc/lxc_process.c
> index bcd59cb..d5e1822 100644
> --- a/src/lxc/lxc_process.c
> +++ b/src/lxc/lxc_process.c
> @@ -28,6 +28,7 @@
>  #include "lxc_process.h"
>  #include "lxc_domain.h"
>  #include "lxc_container.h"
> +#include "lxc_fuse.h"
>  #include "datatypes.h"
>  #include "virfile.h"
>  #include "virpidfile.h"
> @@ -232,7 +233,7 @@ static void virLXCProcessCleanup(virLXCDriverPtr driver,
>                      NULL, xml, NULL);
>          VIR_FREE(xml);
>      }
> -
> +    lxcUnregisterFuse(vm->def);
>      /* Stop autodestroy in case guest is restarted */
>      virLXCProcessAutoDestroyRemove(driver, vm);

If you delayed starting FUSE until after we do unshare(), then the mount
point will automatically go away when the LXC controller process exits,
so we won't need any manual unmount in lxcUnregisterFuse()


Daniel
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