fuse: nfs export special lookups

Implement the get_parent export operation by sending a LOOKUP request with
".." as the name.

Implement looking up an inode by node ID after it has been evicted from
the cache.  This is done by seding a LOOKUP request with "." as the name
(for all file types, not just directories).

The filesystem can set the FUSE_EXPORT_SUPPORT flag in the INIT reply, to
indicate that it supports these special lookups.

Thanks to John Muir for the original implementation of this feature.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: David Teigland <teigland@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 69 insertions, 3 deletions

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 5d3146da64e6..3a876076bdd1 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -363,6 +363,9 @@ struct fuse_conn {
         /** Do not send separate SETATTR request before open(O_TRUNC)  */
         unsigned atomic_o_trunc : 1;
 
+        /** Filesystem supports NFS exporting.  Only set in INIT */
+        unsigned export_support : 1;
+
         /*
          * The following bitfields are only for optimization purposes
          * and hence races in setting them will not cause malfunction
@@ -473,6 +476,9 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
                         int generation, struct fuse_attr *attr,
                         u64 attr_valid, u64 attr_version);
 
+int fuse_lookup_name(struct super_block *sb, u64 nodeid, struct qstr *name,
+                     struct fuse_entry_out *outarg, struct inode **inode);
+
 /**
  * Send FORGET command
  */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 71fa76a48a31..7d2f7d6e22e2 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -562,6 +562,7 @@ struct fuse_inode_handle
 static struct dentry *fuse_get_dentry(struct super_block *sb,
                                       struct fuse_inode_handle *handle)
 {
+        struct fuse_conn *fc = get_fuse_conn_super(sb);
         struct inode *inode;
         struct dentry *entry;
         int err = -ESTALE;
@@ -570,8 +571,27 @@ static struct dentry *fuse_get_dentry(struct super_block *sb,
                 goto out_err;
 
         inode = ilookup5(sb, handle->nodeid, fuse_inode_eq, &handle->nodeid);
-        if (!inode)
-                goto out_err;
+        if (!inode) {
+                struct fuse_entry_out outarg;
+                struct qstr name;
+
+                if (!fc->export_support)
+                        goto out_err;
+
+                name.len = 1;
+                name.name = ".";
+                err = fuse_lookup_name(sb, handle->nodeid, &name, &outarg,
+                                       &inode);
+                if (err && err != -ENOENT)
+                        goto out_err;
+                if (err || !inode) {
+                        err = -ESTALE;
+                        goto out_err;
+                }
+                err = -EIO;
+                if (get_node_id(inode) != handle->nodeid)
+                        goto out_iput;
+        }
         err = -ESTALE;
         if (inode->i_generation != handle->generation)
                 goto out_iput;
@@ -659,11 +679,46 @@ static struct dentry *fuse_fh_to_parent(struct super_block *sb,
         return fuse_get_dentry(sb, &parent);
 }
 
+static struct dentry *fuse_get_parent(struct dentry *child)
+{
+        struct inode *child_inode = child->d_inode;
+        struct fuse_conn *fc = get_fuse_conn(child_inode);
+        struct inode *inode;
+        struct dentry *parent;
+        struct fuse_entry_out outarg;
+        struct qstr name;
+        int err;
+
+        if (!fc->export_support)
+                return ERR_PTR(-ESTALE);
+
+        name.len = 2;
+        name.name = "..";
+        err = fuse_lookup_name(child_inode->i_sb, get_node_id(child_inode),
+                               &name, &outarg, &inode);
+        if (err && err != -ENOENT)
+                return ERR_PTR(err);
+        if (err || !inode)
+                return ERR_PTR(-ESTALE);
+
+        parent = d_alloc_anon(inode);
+        if (!parent) {
+                iput(inode);
+                return ERR_PTR(-ENOMEM);
+        }
+        if (get_node_id(inode) != FUSE_ROOT_ID) {
+                parent->d_op = &fuse_dentry_operations;
+                fuse_invalidate_entry_cache(parent);
+        }
+
+        return parent;
+}
 
 static const struct export_operations fuse_export_operations = {
         .fh_to_dentry   = fuse_fh_to_dentry,
         .fh_to_parent   = fuse_fh_to_parent,
         .encode_fh      = fuse_encode_fh,
+        .get_parent     = fuse_get_parent,
 };
 
 static const struct super_operations fuse_super_operations = {
@@ -695,6 +750,11 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
                                 fc->no_lock = 1;
                         if (arg->flags & FUSE_ATOMIC_O_TRUNC)
                                 fc->atomic_o_trunc = 1;
+                        if (arg->minor >= 9) {
+                                /* LOOKUP has dependency on proto version */
+                                if (arg->flags & FUSE_EXPORT_SUPPORT)
+                                        fc->export_support = 1;
+                        }
                         if (arg->flags & FUSE_BIG_WRITES)
                                 fc->big_writes = 1;
                 } else {
@@ -721,7 +781,7 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
         arg->minor = FUSE_KERNEL_MINOR_VERSION;
         arg->max_readahead = fc->bdi.ra_pages * PAGE_CACHE_SIZE;
         arg->flags |= FUSE_ASYNC_READ | FUSE_POSIX_LOCKS | FUSE_ATOMIC_O_TRUNC |
-                FUSE_BIG_WRITES;
+                FUSE_EXPORT_SUPPORT | FUSE_BIG_WRITES;
         req->in.h.opcode = FUSE_INIT;
         req->in.numargs = 1;
         req->in.args[0].size = sizeof(*arg);