11.12.2012 18:12, Stanislav Kinsbursky пишет:
11.12.2012 18:00, Stanislav Kinsbursky пишет:
11.12.2012 00:28, J. Bruce Fields пишет:
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 ?
Ok, you are right. I was mistaken here.
This is not a exactly lookup, but d_path() problem in svc_export_request().
I.e. without root swapping, d_path() will give not local export path (like "/export")
but something like this "/root/containers_root/export".
We, actually, can do it less in less aggressive way.
I.e. instead root swap and current svc_export_request() implementation:
void svc_export_request(...)
{
<snip>
pth = d_path(&exp->ex_path, *bpp, *blen);
<snip>
}
we can do something like this:
void svc_export_request(...)
{
struct nfsd_net *nn = ...
<snip>
spin_lock(&dcache_lock);
pth = __d_path(&exp->ex_path, &nn->root, *bpp, *blen);
spin_unlock(&dcache_lock);
<snip>
}
No, this won't work. Sorry for noise.
--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
*/
--
Best regards,
Stanislav Kinsbursky
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