[lxc-devel] [PATCH] Remounts bind mounts if read-only flag is provided

[Serge Hallyn]

Quoting Abin Shahab (ashahab at altiscale.com):
> Bind mounts do not honor filesystem mount options. This change will remount filesystems that are bind mounted if there are changes to filesystem mount options, specifically if the mount is readonly.

hi,

Just to make sure I understand what you're saying,

'mount --bind -o ro /a /b' (when done through mount(2)) will not
actually make /b readonly, so we need to do a remount in that case
to get the -o ro to take effect at the vfsmount instead of the sb.
Is that right?

> Signed-off-by: Abin Shahab <ashahab at altiscale.com>
> ---
>  src/lxc/conf.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/src/lxc/conf.c b/src/lxc/conf.c
> index 5938c3e..a3779de 100644
> --- a/src/lxc/conf.c
> +++ b/src/lxc/conf.c
> @@ -1921,10 +1921,12 @@ static int mount_entry(const char *fsname, const char *target,
>  	if ((mountflags & MS_REMOUNT) || (mountflags & MS_BIND)) {
>  		DEBUG("remounting %s on %s to respect bind or remount options",
>  		      fsname ? fsname : "(none)", target ? target : "(none)");
> -
> +		unsigned long rqd_flags = 0;
> +		if (mountflags & MS_RDONLY)
> +			rqd_flags |= MS_RDONLY;
>  #ifdef HAVE_STATVFS
>  		if (statvfs(fsname, &sb) == 0) {
> -			unsigned long required_flags = 0;
> +			unsigned long required_flags = rqd_flags;
>  			if (sb.f_flag & MS_NOSUID)
>  				required_flags |= MS_NOSUID;
>  			if (sb.f_flag & MS_NODEV)
> @@ -1940,7 +1942,7 @@ static int mount_entry(const char *fsname, const char *target,
>  			 * mountflags, then skip the remount
>  			 */
>  			if (!(mountflags & MS_REMOUNT)) {
> -				if (!(required_flags & ~mountflags)) {
> +				if (!(required_flags & ~mountflags) && rqd_flags == 0) {
>  					DEBUG("mountflags already was %lu, skipping remount",
>  						mountflags);
>  					goto skipremount;
> -- 
> 2.1.0
> 
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