[CRIU] [PATCH] mnt: disable the use of pivot_root in case of ramdisk

[Andrew Vagin]

On Sat, Oct 31, 2015 at 11:51:27PM +0100, ismael wrote:
> Le Thu, 29 Oct 2015 13:55:08 +0300,
> Andrew Vagin <avagin at odin.com> a écrit :
> 
> > On Mon, Oct 26, 2015 at 11:01:11PM +0100, Ismaël FEZZAZ wrote:
> > > Signed-off-by: Ismael Fezzaz <i.fezzaz at gmail.com>
> > > ---
> > >  crtools.c            |  5 +++++
> > >  include/cr_options.h |  1 +
> > >  mount.c              | 19 +++++++++++++++++++
> > >  3 files changed, 25 insertions(+)
> > > 
> > > diff --git a/crtools.c b/crtools.c
> > > index d3812a1..6d60421 100644
> > > --- a/crtools.c
> > > +++ b/crtools.c
> > > @@ -253,6 +253,7 @@ int main(int argc, char *argv[], char *envp[])
> > >          { "freeze-cgroup",        required_argument,    0, 1068 },
> > >          { "ghost-limit",        required_argument,    0, 1069 },
> > >          { "irmap-scan-path",        required_argument,    0,
> > > 1070 },
> > > +        { "ramdisk",            no_argument,        0, 1071 },
> > >          { },
> > >      };
> > > 
> > > @@ -498,6 +499,9 @@ int main(int argc, char *argv[], char *envp[])
> > >              if (irmap_scan_path_add(optarg))
> > >                  return -1;
> > >              break;
> > > +        case 10701:
> > > +            opts.ramdisk = true;
> > > +            break;
> > >          case 'M':
> > >              {
> 
> The option number in the switch was wrong, here is the fixed version.
> Sorry for that.
> 
> Signed-off-by: Ismael Fezzaz <i.fezzaz at gmail.com>
> ---
>  crtools.c            |  5 +++++
>  include/cr_options.h |  1 +
>  mount.c              | 19 +++++++++++++++++++
>  3 files changed, 25 insertions(+)
> 
> diff --git a/crtools.c b/crtools.c
> index d3812a1..865b6fc 100644
> --- a/crtools.c
> +++ b/crtools.c
> @@ -253,6 +253,7 @@ int main(int argc, char *argv[], char *envp[])
>  		{ "freeze-cgroup",		required_argument,	0, 1068 },
>  		{ "ghost-limit",		required_argument,	0, 1069 },
>  		{ "irmap-scan-path",		required_argument,	0, 1070 },
> +		{ "ramdisk",			no_argument ,		0, 1071 },
>  		{ },
>  	};
>  
> @@ -498,6 +499,9 @@ int main(int argc, char *argv[], char *envp[])
>  			if (irmap_scan_path_add(optarg))
>  				return -1;
>  			break;
> +		case 1071:
> +			opts.ramdisk = true;
> +			break;
>  		case 'M':
>  			{
>  				char *aux;
> @@ -747,6 +751,7 @@ usage:
>  "  --enable-fs FSNAMES   a comma separated list of filesystem names or \"all\".\n"
>  "                        force criu to (try to) dump/restore these filesystem's\n"
>  "                        mountpoints even if fs is not supported.\n"
> +"  --ramdisk             disable 'pivot_root'.\n"
>  "\n"
>  "* Logging:\n"
>  "  -o|--log-file FILE    log file name\n"
> diff --git a/include/cr_options.h b/include/cr_options.h
> index eac7283..eb89076 100644
> --- a/include/cr_options.h
> +++ b/include/cr_options.h
> @@ -95,6 +95,7 @@ struct cr_options {
>  	bool			overlayfs;
>  	size_t			ghost_limit;
>  	struct list_head	irmap_scan_paths;
> +	bool			ramdisk;
>  };
>  
>  extern struct cr_options opts;
> diff --git a/mount.c b/mount.c
> index aea9807..b8f1b26 100644
> --- a/mount.c
> +++ b/mount.c
> @@ -2246,6 +2246,25 @@ static int cr_pivot_root(char *root)
>  		}
>  	}
>  
> +	if (opts.ramdisk) {

cr_pivot_root() is called twice:

1. to switch root of the root mount namespace

2. to switch root of a sub-mount namespace

This code should be executed only for the first case. And pivot_root
should be used to restore sub-namespaces, because it allow to clean up
of extra mounts.

> +		if (mount(".", "/", NULL, MS_MOVE, NULL)) {
> +			pr_perror("moving . to / failed");
> +			return -1;
> +		}
> +
> +		if (chroot(".")) {
> +			pr_perror("chroot . failed");
> +			return -1;
> +		}
> +
> +		if (chdir("/")) {
> +			pr_perror("chdir / failed");
> +			return -1;
> +		}
> +
> +		return 0;
> +	}
> +
>  	if (mkdtemp(put_root) == NULL) {
>  		pr_perror("Can't create a temporary directory");
>  		return -1;
> -- 
> 1.9.1