On Thu, Dec 06, 2012 at 06:34:47PM +0300, Stanislav Kinsbursky wrote:
> NFSd does lookup. Lookup is done starting from current->fs->root.
> NFSd is a kthread, cloned by kthreadd, and thus have global (but luckely
> unshared) root.
> So we have to swap root to those, which process, started NFSd, has. Because
> that process can be in a container with it's own root.
This doesn't sound right to me.
Which lookups exactly do you see being done relative to
current->fs->root ?
--b.
>
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@xxxxxxxxxxxxx>
> ---
> fs/nfsd/netns.h | 1 +
> fs/nfsd/nfssvc.c | 33 ++++++++++++++++++++++++++++++++-
> 2 files changed, 33 insertions(+), 1 deletions(-)
>
> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> index abfc97c..5c423c6 100644
> --- a/fs/nfsd/netns.h
> +++ b/fs/nfsd/netns.h
> @@ -101,6 +101,7 @@ struct nfsd_net {
> struct timeval nfssvc_boot;
>
> struct svc_serv *nfsd_serv;
> + struct path root;
> };
>
> extern int nfsd_net_id;
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index cee62ab..177bb60 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -392,6 +392,7 @@ int nfsd_create_serv(struct net *net)
>
> set_max_drc();
> do_gettimeofday(&nn->nfssvc_boot); /* record boot time */
> + get_fs_root(current->fs, &nn->root);
> return 0;
> }
>
> @@ -426,8 +427,10 @@ void nfsd_destroy(struct net *net)
> if (destroy)
> svc_shutdown_net(nn->nfsd_serv, net);
> svc_destroy(nn->nfsd_serv);
> - if (destroy)
> + if (destroy) {
> + path_put(&nn->root);
> nn->nfsd_serv = NULL;
> + }
> }
>
> int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
> @@ -533,6 +536,25 @@ out:
> return error;
> }
>
> +/*
> + * This function is actually slightly modified set_fs_root()<F9>
> + */
> +static void nfsd_swap_root(struct net *net)
> +{
> + struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> + struct fs_struct *fs = current->fs;
> + struct path old_root;
> +
> + path_get(&nn->root);
> + spin_lock(&fs->lock);
> + write_seqcount_begin(&fs->seq);
> + old_root = fs->root;
> + fs->root = nn->root;
> + write_seqcount_end(&fs->seq);
> + spin_unlock(&fs->lock);
> + if (old_root.dentry)
> + path_put(&old_root);
> +}
>
> /*
> * This is the NFS server kernel thread
> @@ -559,6 +581,15 @@ nfsd(void *vrqstp)
> current->fs->umask = 0;
>
> /*
> + * We have to swap NFSd kthread's fs->root.
> + * Why so? Because NFSd can be started in container, which has it's own
> + * root.
> + * And so what? NFSd lookup files, and lookup start from
> + * current->fs->root.
> + */
> + nfsd_swap_root(net);
> +
> + /*
> * thread is spawned with all signals set to SIG_IGN, re-enable
> * the ones that will bring down the thread
> */
>
--
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