[PATCH] NFS: Hide NFS server-generated readdir cookies from userland

 NFSv3 currently returns the unsigned 64-bit cookie directly to
 userspace. The following patch causes the kernel to generate
 loff_t offsets for the benefit of userland.
 The current server-generated READDIR cookie is cached in the
 nfs_open_context instead of in filp->f_pos, so we still end up work
 correctly under directory insertions/deletion.

 Signed-off-by: Olivier Galibert <galibert@pobox.com>
 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 92 insertions, 24 deletions

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 2c6a95945684..fceef29c65a3 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -141,7 +141,9 @@ typedef struct {
         struct page     *page;
         unsigned long   page_index;
         u32             *ptr;
-        u64             target;
+        u64             target_cookie;
+        int             target_index;
+        int             current_index;
         struct nfs_entry *entry;
         decode_dirent_t decode;
         int             plus;
@@ -225,14 +227,14 @@ void dir_page_release(nfs_readdir_descriptor_t *desc)
 
 /*
  * Given a pointer to a buffer that has already been filled by a call
- * to readdir, find the next entry.
+ * to readdir, find the next entry with cookie 'desc->target_cookie'.
  *
  * If the end of the buffer has been reached, return -EAGAIN, if not,
  * return the offset within the buffer of the next entry to be
  * read.
  */
 static inline
-int find_dirent(nfs_readdir_descriptor_t *desc, struct page *page)
+int find_dirent(nfs_readdir_descriptor_t *desc)
 {
         struct nfs_entry *entry = desc->entry;
         int             loop_count = 0,
@@ -240,7 +242,7 @@ int find_dirent(nfs_readdir_descriptor_t *desc, struct page *page)
 
         while((status = dir_decode(desc)) == 0) {
                 dfprintk(VFS, "NFS: found cookie %Lu\n", (long long)entry->cookie);
-                if (entry->prev_cookie == desc->target)
+                if (entry->prev_cookie == desc->target_cookie)
                         break;
                 if (loop_count++ > 200) {
                         loop_count = 0;
@@ -252,8 +254,44 @@ int find_dirent(nfs_readdir_descriptor_t *desc, struct page *page)
 }
 
 /*
- * Find the given page, and call find_dirent() in order to try to
- * return the next entry.
+ * Given a pointer to a buffer that has already been filled by a call
+ * to readdir, find the entry at offset 'desc->target_index'.
+ *
+ * If the end of the buffer has been reached, return -EAGAIN, if not,
+ * return the offset within the buffer of the next entry to be
+ * read.
+ */
+static inline
+int find_dirent_index(nfs_readdir_descriptor_t *desc)
+{
+        struct nfs_entry *entry = desc->entry;
+        int             loop_count = 0,
+                        status;
+
+        for(;;) {
+                status = dir_decode(desc);
+                if (status)
+                        break;
+
+                dfprintk(VFS, "NFS: found cookie %Lu at index %d\n", (long long)entry->cookie, desc->current_index);
+
+                if (desc->target_index == desc->current_index) {
+                        desc->target_cookie = entry->cookie;
+                        break;
+                }
+                desc->current_index++;
+                if (loop_count++ > 200) {
+                        loop_count = 0;
+                        schedule();
+                }
+        }
+        dfprintk(VFS, "NFS: find_dirent_index() returns %d\n", status);
+        return status;
+}
+
+/*
+ * Find the given page, and call find_dirent() or find_dirent_index in
+ * order to try to return the next entry.
  */
 static inline
 int find_dirent_page(nfs_readdir_descriptor_t *desc)
@@ -276,7 +314,10 @@ int find_dirent_page(nfs_readdir_descriptor_t *desc)
         /* NOTE: Someone else may have changed the READDIRPLUS flag */
         desc->page = page;
         desc->ptr = kmap(page);         /* matching kunmap in nfs_do_filldir */
-        status = find_dirent(desc, page);
+        if (desc->target_cookie)
+                status = find_dirent(desc);
+        else
+                status = find_dirent_index(desc);
         if (status < 0)
                 dir_page_release(desc);
  out:
@@ -291,7 +332,8 @@ int find_dirent_page(nfs_readdir_descriptor_t *desc)
  * Recurse through the page cache pages, and return a
  * filled nfs_entry structure of the next directory entry if possible.
  *
- * The target for the search is 'desc->target'.
+ * The target for the search is 'desc->target_cookie' if non-0,
+ * 'desc->target_index' otherwise
  */
 static inline
 int readdir_search_pagecache(nfs_readdir_descriptor_t *desc)
@@ -299,7 +341,19 @@ int readdir_search_pagecache(nfs_readdir_descriptor_t *desc)
         int             loop_count = 0;
         int             res;
 
-        dfprintk(VFS, "NFS: readdir_search_pagecache() searching for cookie %Lu\n", (long long)desc->target);
+        if (desc->target_cookie)
+                dfprintk(VFS, "NFS: readdir_search_pagecache() searching for cookie %Lu\n", (long long)desc->target_cookie);
+        else
+                dfprintk(VFS, "NFS: readdir_search_pagecache() searching for cookie number %d\n", desc->target_index);
+
+        /* Always search-by-index from the beginning of the cache */
+        if (!(desc->target_cookie)) {
+                desc->page_index = 0;
+                desc->entry->cookie = desc->entry->prev_cookie = 0;
+                desc->entry->eof = 0;
+                desc->current_index = 0;
+        }
+
         for (;;) {
                 res = find_dirent_page(desc);
                 if (res != -EAGAIN)
@@ -332,11 +386,12 @@ int nfs_do_filldir(nfs_readdir_descriptor_t *desc, void *dirent,
         struct file     *file = desc->file;
         struct nfs_entry *entry = desc->entry;
         struct dentry   *dentry = NULL;
+        struct nfs_open_context *ctx = file->private_data;
         unsigned long   fileid;
         int             loop_count = 0,
                         res;
 
-        dfprintk(VFS, "NFS: nfs_do_filldir() filling starting @ cookie %Lu\n", (long long)desc->target);
+        dfprintk(VFS, "NFS: nfs_do_filldir() filling starting @ cookie %Lu\n", (long long)entry->cookie);
 
         for(;;) {
                 unsigned d_type = DT_UNKNOWN;
@@ -356,10 +411,11 @@ int nfs_do_filldir(nfs_readdir_descriptor_t *desc, void *dirent,
                 }
 
                 res = filldir(dirent, entry->name, entry->len, 
-                              entry->prev_cookie, fileid, d_type);
+                              file->f_pos, fileid, d_type);
                 if (res < 0)
                         break;
-                file->f_pos = desc->target = entry->cookie;
+                file->f_pos++;
+                desc->target_cookie = entry->cookie;
                 if (dir_decode(desc) != 0) {
                         desc->page_index ++;
                         break;
@@ -369,10 +425,12 @@ int nfs_do_filldir(nfs_readdir_descriptor_t *desc, void *dirent,
                         schedule();
                 }
         }
+        ctx->dir_pos        = file->f_pos;
+        ctx->dir_cookie     = desc->target_cookie;
         dir_page_release(desc);
         if (dentry != NULL)
                 dput(dentry);
-        dfprintk(VFS, "NFS: nfs_do_filldir() filling ended @ cookie %Lu; returning = %d\n", (long long)desc->target, res);
+        dfprintk(VFS, "NFS: nfs_do_filldir() filling ended @ cookie %Lu; returning = %d\n", (long long)desc->target_cookie, res);
         return res;
 }
 
@@ -398,14 +456,14 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc, void *dirent,
         struct page     *page = NULL;
         int             status;
 
-        dfprintk(VFS, "NFS: uncached_readdir() searching for cookie %Lu\n", (long long)desc->target);
+        dfprintk(VFS, "NFS: uncached_readdir() searching for cookie %Lu\n", (long long)desc->target_cookie);
 
         page = alloc_page(GFP_HIGHUSER);
         if (!page) {
                 status = -ENOMEM;
                 goto out;
         }
-        desc->error = NFS_PROTO(inode)->readdir(file->f_dentry, cred, desc->target,
+        desc->error = NFS_PROTO(inode)->readdir(file->f_dentry, cred, desc->target_cookie,
                                                 page,
                                                 NFS_SERVER(inode)->dtsize,
                                                 desc->plus);
@@ -414,7 +472,7 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc, void *dirent,
         desc->ptr = kmap(page);         /* matching kunmap in nfs_do_filldir */
         if (desc->error >= 0) {
                 if ((status = dir_decode(desc)) == 0)
-                        desc->entry->prev_cookie = desc->target;
+                        desc->entry->prev_cookie = desc->target_cookie;
         } else
                 status = -EIO;
         if (status < 0)
@@ -435,13 +493,15 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc, void *dirent,
         goto out;
 }
 
-/* The file offset position is now represented as a true offset into the
- * page cache as is the case in most of the other filesystems.
+/* The file offset position represents the dirent entry number.  A
+   last cookie cache takes care of the common case of reading the
+   whole directory.
  */
 static int nfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
 {
         struct dentry   *dentry = filp->f_dentry;
         struct inode    *inode = dentry->d_inode;
+        struct nfs_open_context *ctx = filp->private_data;
         nfs_readdir_descriptor_t my_desc,
                         *desc = &my_desc;
         struct nfs_entry my_entry;
@@ -458,17 +518,22 @@ static int nfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
         }
 
         /*
-         * filp->f_pos points to the file offset in the page cache.
-         * but if the cache has meanwhile been zapped, we need to
-         * read from the last dirent to revalidate f_pos
-         * itself.
+         * filp->f_pos points to the dirent entry number.
+         * ctx->dir_pos has the number of the cached cookie.  We have
+         * to either find the entry with the appropriate number or
+         * revalidate the cookie.
          */
         memset(desc, 0, sizeof(*desc));
 
         desc->file = filp;
-        desc->target = filp->f_pos;
         desc->decode = NFS_PROTO(inode)->decode_dirent;
         desc->plus = NFS_USE_READDIRPLUS(inode);
+        desc->target_index = filp->f_pos;
+
+        if (filp->f_pos == ctx->dir_pos)
+                desc->target_cookie = ctx->dir_cookie;
+        else
+                desc->target_cookie = 0;
 
         my_entry.cookie = my_entry.prev_cookie = 0;
         my_entry.eof = 0;
@@ -478,9 +543,10 @@ static int nfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
 
         while(!desc->entry->eof) {
                 res = readdir_search_pagecache(desc);
+
                 if (res == -EBADCOOKIE) {
                         /* This means either end of directory */
-                        if (desc->entry->cookie != desc->target) {
+                        if (desc->target_cookie && desc->entry->cookie != desc->target_cookie) {
                                 /* Or that the server has 'lost' a cookie */
                                 res = uncached_readdir(desc, dirent, filldir);
                                 if (res >= 0)
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 8a8d57d9d660..9fa02e7984ac 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -891,6 +891,8 @@ struct nfs_open_context *alloc_nfs_open_context(struct dentry *dentry, struct rp
                 ctx->state = NULL;
                 ctx->lockowner = current->files;
                 ctx->error = 0;
+                ctx->dir_pos = 0;
+                ctx->dir_cookie = 0;
         }
         return ctx;
 }