Btrfs: Implement our own copy of the nfsd readdir hack, for older kernels

Date: Wed, 6 Aug 2008 19:42:33 +0100
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 102 insertions, 2 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 266ca5514b33..0da1ae4ee407 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1915,7 +1915,8 @@ static unsigned char btrfs_filetype_table[] = {
         DT_UNKNOWN, DT_REG, DT_DIR, DT_CHR, DT_BLK, DT_FIFO, DT_SOCK, DT_LNK
 };
 
-static int btrfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
+static int btrfs_real_readdir(struct file *filp, void *dirent,
+                              filldir_t filldir)
 {
         struct inode *inode = filp->f_dentry->d_inode;
         struct btrfs_root *root = BTRFS_I(inode)->root;
@@ -2064,6 +2065,101 @@ err:
         return ret;
 }
 
+/* Kernels earlier than 2.6.28 still have the NFS deadlock where nfsd
+   will call the file system's ->lookup() method from within its
+   filldir callback, which in turn was called from the file system's
+   ->readdir() method. And will deadlock for many file systems. */
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,28)
+
+struct nfshack_dirent {
+        u64             ino;
+        loff_t          offset;
+        int             namlen;
+        unsigned int    d_type;
+        char            name[];
+};
+
+struct nfshack_readdir {
+        char            *dirent;
+        size_t          used;
+};
+
+
+
+static int btrfs_nfshack_filldir(void *__buf, const char *name, int namlen,
+                              loff_t offset, u64 ino, unsigned int d_type)
+{
+        struct nfshack_readdir *buf = __buf;
+        struct nfshack_dirent *de = (void *)(buf->dirent + buf->used);
+        unsigned int reclen;
+
+        reclen = ALIGN(sizeof(struct nfshack_dirent) + namlen, sizeof(u64));
+        if (buf->used + reclen > PAGE_SIZE)
+                return -EINVAL;
+
+        de->namlen = namlen;
+        de->offset = offset;
+        de->ino = ino;
+        de->d_type = d_type;
+        memcpy(de->name, name, namlen);
+        buf->used += reclen;
+
+        return 0;
+}
+
+static int btrfs_nfshack_readdir(struct file *file, void *dirent,
+                                 filldir_t filldir)
+{
+        struct nfshack_readdir buf;
+        struct nfshack_dirent *de;
+        int err;
+        int size;
+        loff_t offset;
+
+        buf.dirent = (void *)__get_free_page(GFP_KERNEL);
+        if (!buf.dirent)
+                return -ENOMEM;
+
+        offset = file->f_pos;
+
+        while (1) {
+                unsigned int reclen;
+
+                buf.used = 0;
+
+                err = btrfs_real_readdir(file, &buf, btrfs_nfshack_filldir);
+                if (err)
+                        break;
+
+                size = buf.used;
+
+                if (!size)
+                        break;
+
+                de = (struct nfshack_dirent *)buf.dirent;
+                while (size > 0) {
+                        offset = de->offset;
+
+                        if (filldir(dirent, de->name, de->namlen, de->offset,
+                                    de->ino, de->d_type))
+                                goto done;
+                        offset = file->f_pos;
+
+                        reclen = ALIGN(sizeof(*de) + de->namlen,
+                                       sizeof(u64));
+                        size -= reclen;
+                        de = (struct nfshack_dirent *)((char *)de + reclen);
+                }
+        }
+
+ done:
+        free_page((unsigned long)buf.dirent);
+        file->f_pos = offset;
+
+        return err;
+}
+#endif
+
 int btrfs_write_inode(struct inode *inode, int wait)
 {
         struct btrfs_root *root = BTRFS_I(inode)->root;
@@ -3623,7 +3719,11 @@ static struct inode_operations btrfs_dir_ro_inode_operations = {
 static struct file_operations btrfs_dir_file_operations = {
         .llseek         = generic_file_llseek,
         .read           = generic_read_dir,
-        .readdir        = btrfs_readdir,
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,28)
+        .readdir        = btrfs_nfshack_readdir,
+#else /* NFSd readdir/lookup deadlock is fixed */
+        .readdir        = btrfs_real_readdir,
+#endif
         .unlocked_ioctl = btrfs_ioctl,
 #ifdef CONFIG_COMPAT
         .compat_ioctl   = btrfs_ioctl,