fuse: Add support for d_canonical_path

Allows FUSE to report to inotify that it is acting
as a layered filesystem. The userspace component
returns a string representing the location of the
underlying file. If the string cannot be resolved
into a path, the top level path is returned instead.

bug: 23904372
Change-Id: Iabdca0bbedfbff59e9c820c58636a68ef9683d9f
Signed-off-by: Daniel Rosenberg <drosen@google.com>

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 8eb5a0992658129ebdea8462dbc302af65665fd2..9c361adaab11edbdfb3e6e8259ccd87e2bbe461d 100644 (file)
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -13,6 +13,7 @@
 #include <linux/poll.h>
 #include <linux/uio.h>
 #include <linux/miscdevice.h>
+#include <linux/namei.h>
 #include <linux/pagemap.h>
 #include <linux/file.h>
 #include <linux/slab.h>
@@ -1871,6 +1872,10 @@ static ssize_t fuse_dev_do_write(struct fuse_conn *fc,
        spin_unlock(&fc->lock);
 
        err = copy_out_args(cs, &req->out, nbytes);
+       if (req->in.h.opcode == FUSE_CANONICAL_PATH) {
+               req->out.h.error = kern_path((char *)req->out.args[0].value, 0,
+                                                       req->canonical_path);
+       }
        fuse_copy_finish(cs);
 
        spin_lock(&fc->lock);

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index e67b13de2ebc463b9be8c3bea57304e3af561454..7668bbcd444af51a51e11bd9a7a536ae11ab5d72 100644 (file)
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -252,6 +252,50 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
        return 1;
 }
 
+/*
+ * Get the canonical path. Since we must translate to a path, this must be done
+ * in the context of the userspace daemon, however, the userspace daemon cannot
+ * look up paths on its own. Instead, we handle the lookup as a special case
+ * inside of the write request.
+ */
+static void fuse_dentry_canonical_path(const struct path *path, struct path *canonical_path) {
+       struct inode *inode = path->dentry->d_inode;
+       struct fuse_conn *fc = get_fuse_conn(inode);
+       struct fuse_req *req;
+       int err;
+       char *path_name;
+
+       req = fuse_get_req(fc, 1);
+       err = PTR_ERR(req);
+       if (IS_ERR(req))
+               goto default_path;
+
+       path_name = (char*)__get_free_page(GFP_KERNEL);
+       if (!path_name) {
+               fuse_put_request(fc, req);
+               goto default_path;
+       }
+
+       req->in.h.opcode = FUSE_CANONICAL_PATH;
+       req->in.h.nodeid = get_node_id(inode);
+       req->in.numargs = 0;
+       req->out.numargs = 1;
+       req->out.args[0].size = PATH_MAX;
+       req->out.args[0].value = path_name;
+       req->canonical_path = canonical_path;
+       req->out.argvar = 1;
+       fuse_request_send(fc, req);
+       err = req->out.h.error;
+       fuse_put_request(fc, req);
+       free_page((unsigned long)path_name);
+       if (!err)
+               return;
+default_path:
+       canonical_path->dentry = path->dentry;
+       canonical_path->mnt = path->mnt;
+       path_get(canonical_path);
+}
+
 static int invalid_nodeid(u64 nodeid)
 {
        return !nodeid || nodeid == FUSE_ROOT_ID;
@@ -259,6 +303,7 @@ static int invalid_nodeid(u64 nodeid)
 
 const struct dentry_operations fuse_dentry_operations = {
        .d_revalidate   = fuse_dentry_revalidate,
+       .d_canonical_path = fuse_dentry_canonical_path,
 };
 
 int fuse_valid_type(int m)

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 5ced199b50bbb19a9dcd8fb42313de4afba26d6c..93f861a6d36dd33bdac8febf40bcc076d54346ee 100644 (file)
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -348,6 +348,9 @@ struct fuse_req {
        /** Inode used in the request or NULL */
        struct inode *inode;
 
+       /** Path used for completing d_canonical_path */
+       struct path *canonical_path;
+
        /** AIO control block */
        struct fuse_io_priv *io;
 

diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 60bb2f9f7b74272ae30e9119ded495100e6934b6..c5902767c595e64dc8145304384be936b9f6f7ef 100644 (file)
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -343,6 +343,7 @@ enum fuse_opcode {
        FUSE_BATCH_FORGET  = 42,
        FUSE_FALLOCATE     = 43,
        FUSE_READDIRPLUS   = 44,
+       FUSE_CANONICAL_PATH= 2016,
 
        /* CUSE specific operations */
        CUSE_INIT          = 4096,